Physiology or Medicine
Victor Ambros and Gary Ruvkun discovered microRNA, a new class of tiny RNA molecules that play a crucial role in gene regulation. Their groundbreaking discovery in the small worm C. elegans revealed a completely new principle of gene regulation. This turned out to be essential for multicellular organisms, including humans. MicroRNAs are proving to be fundamentally important for how organisms develop and function.
Physics
John Hopfield introduced a spin model that can store and reconstruct information. Geoffrey Hinton built on Hopfield’s idea to invent the Boltzmann Machine, that is able to learn from examples to reconstruct a set of desired patterns. He also popularized and improved Backpropagation of Errors, a method actually used in today’s advanced AI technology (e.g. Deep Learning).
Chemistry
The Nobel Prize in Chemistry 2024 is about proteins, life’s ingenious chemical tools. David Baker has succeeded with the almost impossible feat of building entirely new kinds of proteins. Demis Hassabis and John Jumper have developed an AI model to solve a 50-year-old problem: predicting proteins’ complex structures. These discoveries hold enormous potential.
Seminars
Date:
17
November, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Yet Another Approach to Loschmidt's Paradox
Dr. Lev Melnikovsky | Department of Molecular Chemistry and Materials Science
Protein function is the combined product of chemical and mechanical interactions encoded in the gene. Thus, the function of enzymes relies on finetuning the chemical groups at the active site, but also on large-scale mechanical motions, allowing enzymes to bind to substrates selectively, reach the transition state, and release products. We will discuss recent work aiming to probe directly the linkage between these collective internal motions and the functionality of enzymes, using nano-rheological measurements, AI-prediction of point mutation effects, and physical theory. This work proposes a physical view of enzymes as viscoelastic catalytic machines with sequence-encoded mechanical specifications, which are modulated via long-ranged force transduction.
In this two-part talk, I will try to cover two separate lines of research: Machine learning of antibiotic resistance and AI-driven Science. In the first half, I will describe our efforts to understand and predict antibiotic resistance at the single patient level. I will describe a series of experimental-computational methodologies for following and identifying recurrent patterns in the evolution of antibiotic resistance in the lab and in the clinic. Combined with machine-learning approaches applied to electronic patient records, these tools lead to predictive diagnostics of antibiotic resistance and algorithms for personalized treatments of microbial infections. In the second part of the talk, we will shift gear and talk about AI-driven science. I will describe and demo “data-to-paper”: a platform that autonomously guides LLMs (like ChatGPT) to perform entire research cycles. Provided with data alone, data-to-paper can raise hypotheses, design research plans, write and debug analysis codes, generate and interpret results, and write complete research papers. Automatic information-tracing through the process creates manuscripts in which results, methods and data are programmatically chained. Our work thereby demonstrates a potential for AI-driven acceleration of scientific discovery while enhancing, rather than jeopardizing, traceability, transparency and verifiability. I will describe the strengths of the approach as well as limitations and challenges.
Prof. Kishony would be available to discuss with students and
postdocs after his seminar (2:15 pm - 3 pm).
So we encourage interested students and postdocs to stay after his talk!
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Seminars
Date:
13
October, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Statistical Physics of Multicomponent Systems with Non-Reciprocal Interactions
Statistical Physics of Multicomponent Systems with Non-Reciprocal Interactions
Non-reciprocal interactions, in which the effect of “A” on “B” differs from that of “B” on “A”, effectively emerge in complex systems such as macromolecules, cells, and humans. While a mean-field description of many-body systems with non-reciprocal interactions often predicts oscillatory states, it remains an open question whether such states are real ``phases of matter”, i.e., if they survive fluctuations in spatially-extended systems of arbitrary size. We address this question by studying a non-reciprocal generalization of the most paradigmatic statistical mechanical system: the Ising model. Our results show that an oscillatory phase is destroyed by fluctuations in two dimensions through the proliferation of discrete spiral defects, but is stabilized in three dimensions where non-reciprocity changes the critical exponents from Ising to XY. Finally, we demonstrate how non-reciprocity combined with agent motility leads to new inhomogeneous time-dependent states, that can emerge in models of social behavior.
After a brief introduction related to ultralight (pseudo) scalar dark matter, we shall describe the current status of searches for ultralight dark matter (UDM). We explain why modern clocks can be used to search for both scalar and axion dark matter fields. We review existing and new types of well-motivated models of UDM and argue that they all share one key ingredient - their dominant coupling is to the QCD/nuclear sector.
This is very exciting as we are amidst a revolution in the field of dark matter searches as laser excitation of Th-229 with effective precision of 1:10^13 has been recently achieved, which as we show, is already probing uncharted territory of models. Furthermore, Th-229-based nuclear clock can potentially improve the sensitivity to physics of dark matter and beyond by factor of 10^10! It has several important implications to be discussed.
Seminars
Date:
07
July, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
What does the system “care about”?
Empirical approaches to identifying biological regulation
Prof. Naama Brenner | Dept. of Chemical Engineering & Network Biology Research Lab, Technion
Biological systems regulate their action at multiple levels of organization, from molecular circuits to physiological function. This “homeostasis” maintains stability of the system in the face of external and internal perturbation. How exactly this is achieved remains a topic of ongoing investigation; challenges are high dimensionality, many coupled positive and negative feedback loops, conflicting regulation demands and interaction with the environment.
Here I will introduce an empirical approach to the fundamental question – how do we know what it is that the system really “cares about”? What variable, or combination of variables, is under regulation? Two data-driven methods will be presented. one based on statistical analysis and applied to bacterial growth and division, revealing a hierarchy of regulation – from tightly regulated to sloppy variables. The second is based on a machine-learning algorithm we developed to identify regulation with minimal assumptions. This provides a different angle on the problem and highlights directions for future research.
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Seminars
Date:
23
June, 2024
Sunday
Hour: 12:45-14:30
The Clore Center for Biological Physics
The role of sign indefinite invariants in shaping turbulent cascades.
Our work answers a nearly 60-year quest to derive the turbulent spectrum of weakly interacting internal gravity waves from first principles. The classical wave-turbulence approach didn’t work, as the underlying equation, both in 2D and 3D, is an anisotropic, non-canonical Hamiltonian equation.
A key consequence of the non-canonical Hamiltonian is the conservation of a sign-indefinite quadratic invariant alongside the sign-definite quadratic energy. In 2D, this allows us to derive a much simpler kinetic equation. We leverage this simplification into the derivation of solutions of the kinetic equation, one of which is the turbulent spectrum of weakly interacting 2D internal gravity waves. Our spectrum exactly matches the phenomenological oceanic Garrett-Munk spectrum in the limit of large vertical wave numbers and zero rotation.
This talk is based on recent joint works with Oliver Bühler and Jalal Shatah
arXiv:2311.04183 (to appear soon in PRL).
arXiv:2406.06010.
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Colloquia
Date:
20
June, 2024
Thursday
Hour: 11:15-12:30
Physics colloquium
Stochastic resonance in polymer solution channel flow
A cooperative resonance effect in a stochastic nonlinear dynamical system subjected to external weak periodic forcing, called stochastic resonance (SR), has been extensively studied for the past forty years. Here I discuss the experimentally unexpected observation of SR above an elastic non-modal instability of an inertia-less channel flow of polymer solution (much more complicated than stochastic dynamical flow) due to finite-size white noise perturbations. This flow is shown to be linearly stable similar to Newtonian parallel shear flow. First, I briefly describe viscoelastic flow with curved streamlines, where linear elastic normal mode instability at the critical Weissenberg number, Wic, has been observed and characterized, and the elastic instability mechanism has been explained and experimentally validated. Furthermore, at Wi>>Wic, “elastic turbulence” (ET), a chaotic flow arising via secondary instability, is experimentally discovered, characterized and theoretically explained, while elastic instability in straight channel flow is found from the direct transition from laminar to chaotic flow in the transition flow regime is found. At the secondary instability, ET is observed, and further on the next transition to the unexpected drag reduction flow regime takes place, accompanied by elastic waves previously discovered and characterized earlier. Moreover, we propose and experimentally validate a mechanism of amplification of the wall normal fluctuating vortices by the elastic waves. The elastic waves play the key role in the energy transfer from the main flow to the wall-normal fluctuating vortices. Finally, we report on recently discovered SRs only in a limited subrange of weak elastic waves just above Wic, their characterization, and their role in the transition to a chaotic flow.
Seminars
Date:
10
June, 2024
Monday
Hour: 13:00-14:00
The Clore Center for Biological Physics- Special seminar
Mixing Artificial and Natural Intelligence: From Statistical Mechanics to AI and Back
This presentation will outline recent evolution of AI methodologies, focusing on the emergence of Diffusion Models of AI inspired by non-equilibrium statistical mechanics, Transformers, and Reinforcement Learning. These innovations are revolutionizing our approach to reduced, Lagrangian turbulence modeling and are instrumental in formulating and solving new challenges, such as swimming navigation in chaotic environments.
More generally, attendees will gain insights into the synergy between AI and natural sciences and understand how this symbiosis is shaping the future of scientific research. This comprehensive vision is relevant to theoretical physicists, applied mathematicians, and computer scientists alike.
Colloquia
Date:
10
June, 2024
Monday
Hour: 11:15-12:30
Physics Colloquium
OBSERVATION OF FRACTIONAL QUANTUM ANOMALOUS HALL EFFECT
The interplay between spontaneous symmetry breaking and topology can result in exotic quantum states of matter. A celebrated example is the quantum anomalous Hall (QAH) effect, which exhibits an integer quantum Hall effect at zero magnetic field due to topologically nontrivial bands and intrinsic magnetism. In the presence of strong electron-electron interactions, fractional-QAH (FQAH) effect at zero magnetic field can emerge, which is a lattice analog of fractional quantum Hall effect without Landau level formation. In this talk, I will present experimental observation of FQAH effect in twisted MoTe2 bilayer, using combined magneto-optical and -transport measurements. In addition, we find an anomalous Hall state near the filling factor -1/2, whose behavior resembles that of the composite Fermi liquid phase in the half-filled lowest Landau level of a two-dimensional electron gas at high magnetic field. Direct observation of the FQAH and associated effects paves the way for researching charge fractionalization and anyonic statistics at zero magnetic field.
Reference
1. Observation of Fractionally Quantized Anomalous Hall Effect, Heonjoon Park et al., Nature, https://www.nature.com/articles/s41586-023-06536-0 (2023);
2. Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer, Jiaqi Cai et al., Nature, https://www.nature.com/articles/s41586-023-06289-w (2023);
3. Programming Correlated Magnetic States via Gate Controlled Moiré Geometry, Eric Anderson et al., Science, https://www.science.org/doi/full/10.1126/science.adg4268 (2023).
Colloquia
Date:
06
June, 2024
Thursday
Hour: 11:15-12:30
Physics Colloquium
Emergent Quantum Phenomena in Crystalline Multilayer Graphene
Condensed matter physics has witnessed emergent quantum phenomena driven by electron correlation and topology. Such phenomena have been mostly observed in conventional crystalline materials where flat electronic bands are available. In recent years, moiré superlattices built upon two-dimensional (2D) materials emerged as a new platform to engineer and study electron correlation and topology. In this talk, I will introduce a family of synthetic quantum materials, based on crystalline multilayer graphene, as a new platform to engineer and study emergent phenomena driven by many-body interactions. This system hosts flat-bands in highly ordered conventional crystalline materials and dresses them with proximity effects enabled by rich structures in 2D van der Waals heterostructures. As a result, a rich spectrum of emergent phenomena including correlated insulators, spin/valley-polarized metals, integer and fractional quantum anomalous Hall effects, as well as superconductivities have been observed in our experiments. I will also discuss the implications of these observations for topological quantum computation.
References:
[1] Han, T., Lu, Z., Scuri, G. et al. Nat. Nanotechnol. 19, 181–187 (2024). [2] Han, T., Lu, Z., Scuri, G. et al. Nature 623, 41–47 (2023). [3] Han, T., Lu, Z., Yao, Y. et al. Science 384,647-651(2024). [4] Lu, Z., Han, T., Yao, Y. et al. Nature 626, 759–764 (2024). [5] Yang, J., Chen, G., Han, T. et al. Science, 375(6586), pp.1295-1299. (2022)
Seminars
Date:
04
June, 2024
Tuesday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Flexoelectricity versus Electrostatics in Polar Nematic Liquid Crystals
In the most common phase of liquid crystals, called the nematic phase, molecules are aligned up or down along some axis, so that the net electrostatic polarization is zero. Recent experiments have found a new class of liquid crystals, called ferroelectric nematic, in which molecules align predominantly in one direction along the axis, leading to a nonzero polarization. From the perspective of statistical mechanics, the ferroelectric nematic phase has two special features. First, it has flexoelectricity, meaning that the polarization induces a splay of the molecular orientation. Second, the energy includes an electrostatic interaction, which favors a domain structure. In this talk, we discuss the competition between those two effects to control the phase behavior.
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Seminars
Date:
26
May, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Phages vs bacteria warfare: co-evolution and intelligence gathering
The warfare between bacteria and phages - viruses that infect bacteria - has been raging for billions of years. During this time both sides have evolved various attack and defense systems. In this talk I will describe 3 related projects: 1. Is there an optimal number of such defense or anti-defense systems? 2. How can different phages which prey on the same bacteria co-exist, in contradiction with the expected competitive exclusion? 3. Some phages have developed the ability to garner environmental information, enabling them to make more "intelligent" decisions. How much is such intelligence worth, in terms of other resources?
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Colloquia
Date:
23
May, 2024
Thursday
Hour: 11:15-12:30
Physics Colloquium
Quantum Dot Physics Using Atomic Defects in Ultrathin Tunnel Barriers
Quantum dots (QDs) are conducting regions which can localize few charge carriers, and where the energy spectrum is dominated by Coulomb repulsion. QDs can be as large as few hundreds of nanometers, or as small as a single molecule, their sizes depending on their physical realization – whether in two-dimensional materials, nanowires, molecular systems.
In my talk I will describe our work on a new type of an atomically-sized QD, realized in defects residing in ultrathin two-dimensional insulators. These defect-dots are found in layered materials such as hexagonal Boron Nitride (hBN), which we study by their assembly into stacked devices. By using graphene electrodes, we are able to electronically couple to the QD, while allowing the QD energy to be externally tuned exploiting the penetration of electric field through graphene.
A consequence of the structure of our devices is that the defect QDs are placed at atomic distance to the conductors on both sides. I will show how the presence of such energy-tunable, atomically sized QDs at nanometer proximity to other conducting systems opens new opportunities for sensitive measurements, including use of QDs as highly sensitive spectrometers [1], or as single electron transistors, unique in their sensitivity to local electric fields at the nanometer scale [2]. I will discuss our future prospects of using defect QDs as quantum sensors.
References
1. Devidas, T.R., I. Keren, and H. Steinberg, Spectroscopy of NbSe2 Using Energy-Tunable Defect-Embedded Quantum Dots. Nano Letters, 2021. 21(16): p. 6931-6937.
2. Keren, I., et al., Quantum-dot assisted spectroscopy of degeneracy-lifted Landau levels in graphene. Nature Communications, 2020. 11(1): p. 3408.
We study the assembly of programmable quasi-2D DNA compartments as
“artificial cells” from the individual cellular level to multicellular communication.
We will describe work on autonomous synthesis and assembly of cellular
machines, collective modes of synchrony in a 2D lattice of ~1000
compartments, and a first look at the birth of proteins on a single DNA.
Colloquia
Date:
09
May, 2024
Thursday
Hour: 11:15-12:30
Physics colloquium
Synergistic progress in plasmas:
from fusion to astrophysics
Over the last decade, several exciting directions have been initiated by laser-driven plasmas,
e.g., compact particle accelerators, inertial fusion and laboratory astrophysics. The first has
known rapid progress, in terms of current, energy, stability; fusion has gone through a historic
step, with the news of ignition being achieved at NIF in 2022; and laboratory astrophysics has
known also spectacular developments, demonstrating the possibility to perform fully scalable
experiments relevant to various objects such as forming stars and supernovae. A particularly
interesting aspect is that all these fields are strongly synergistic, i.e., that advances in one can
push the others as well. I will present examples of such synergies, through recent results
we have obtained in all these domains, and in particular how ultra-bright neutron beams
can be developed using latest generation multi-PW lasers [1,2]. These could open interesting
perspectives in terms of cargo inspection, but also for fusion plasma measurements.
I will also show how fusion can benefit from external magnetization [3]. Finally, I will discuss
advances in laboratory astrophysics, particularly the first-stage acceleration of ions leading to
cosmic rays [4,5], understanding the universal nature of collimated outflows in the Universe [6],
and probing the intricacy of 3D magnetic reconnection [7]
[1] High-flux neutron generation by laser-accelerated ions from single-and double-layer targets, V Horný et al.,
Scientific Reports 12 (1), 19767, 2022
[2] Numerical investigation of spallation neutrons generated from petawatt-scale laser-driven proton beams,
B Martinez et al., Matter and Radiation at Extremes 7 (2), 024401, 2022
[3] Dynamics of nanosecond laser pulse propagation and of associated instabilities in a magnetized underdense
plasma, W. Yao et al., https://doi.org/10.48550/arXiv.2211.06036
[4] Laboratory evidence for proton energization by collisionless shock surfing, W Yao et al.,
Nature Physics 17 (10), 1177-1182, 2021
[5] Enhancement of the Nonresonant Streaming Instability by Particle Collisions, A Marret et al.,
Physical Review Letters 128 (11), 115101, 2022
[6] Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field, G Revet et al.,
Nature communications 12 (1), 762, 2021
[7] Laboratory evidence of magnetic reconnection hampered in obliquely interacting flux tubes, S Bolaños et al.,
Nature Communications 13 (1), 6426, 2022
We study the assembly of programmable quasi-2D DNA compartments as “artificial cells”, from the individual cellular level to multicellular communication. We will describe work on autonomous synthesis and assembly of cellular machines, collective modes of synchrony in a 2D lattice of ~1000 compartments, and a first look at the birth of proteins on a single DNA.
Seminars
Date:
07
April, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Odd Mechanical Screening: From Metamaterial to Continuum Mechanics of Disordered Solids
Prof. Michael Moshe | Hebrew University in Jerusalem
Holes in elastic metamaterials, defects in 2D curved crystals, localized plastic deformations in amorphous solids and T1 transitions in epithelial tissue, are typical realizations of stress-relaxation mechanisms in different solid-like structures, interpreted as mechanical screening.
In this talk I will present a mechanical screening theory that generalizes classical theories of solids, and introduces new moduli that are missing from the classical theories. Contrary to its electrostatic analog, the screening theory in solids is richer even in the linear case, with multiple screening regimes, predicting qualitatively new mechanical responses.
The theory is tested in different physical systems, including disordered granular solids that do not have a continuous mechanical description. These materials are shown to violate energy conservation and are best described by Odd-Screening: a screening model that does not derive from an energy function. Experiments reveal a mechanical response that is strictly different from classical solid theory and is completely consistent with our mechanical-screening theory. Finally, I will discuss the relevance of this theory to 3D solids and a new Hexatic-like state in 3D matter.
Draw an arbitrary open curve on the plane and copy it multiple times to form a translationally invariant infinite trajectory. Then, incline the plane slightly and ask yourself: can one chisel a stone that will roll exactly down this infinite trajectory?
We will examine this question in practice and theory. Intriguing links to optics and quantum systems will be discussed. Bringing a tennis ball or a baseball is always recommended.
Eckmann et al. Tumbling downhill along a given curve. Am Math Soc Notices - in press.
Sobolev et al. Solid-body trajectoids shaped to roll along desired pathways. Nature 2023.
Colloquia
Date:
21
March, 2024
Thursday
Hour: 11:15-12:30
Physics Colloquium
Fractional statistics of anyons in mesoscopic colliders
In three-dimensional space, elementary particles are divided between fermions and bosons according to the properties of symmetry of the wave function describing the state of the system when two particles are exchanged. When exchanging two fermions, the wave function acquires a phase, φ=π. On the other hand, in the case of bosons, this phase is zero, φ=0. This difference leads to deeply distinct collective behaviors between fermions, which tend to exclude themselves, and bosons which tend to bunch together. The situation is different in two-dimensional systems which can host exotic quasiparticles, called anyons, which obey intermediate quantum statistics characterized by a phase φ varying between 0 and π [1,2].
For example in the fractional quantum Hall regime, obtained by applying a strong magnetic field perpendicular to a two-dimensional electron gas, elementary excitations carry a fractional charge [3,4] and have been predicted to obey fractional statistics [1,2] with an exchange phase φ=π/m (where m is an odd integer). Using metallic gates deposited on top of the electron gas, beam-splitters of anyon beams can be implemented. I will present how the fractional statistics of anyons can be revealed in collider geometries, where anyon sources are placed at the input of a beam-splitter [5,6]. The partitioning of anyon beams is characterized by the formation of packets of anyons at the splitter output. This results in the observation of strong negative correlations of the electrical current, which value is governed by the anyon fractional exchange phase φ [5,7].
[1] B. I. Halperin, Phys. Rev. Lett. 52, 1583–1586 (1984).
[2] D. Arovas, J. R. Schrieffer, F. Wilczek, Phys. Rev. Lett. 53, 722–723 (1984).
[3] R. de Picciotto et al., Nature 389, 162–164 (1997).
[4] L. Saminadayar, D. C. Glattli, Y. Jin, B. Etienne, Phys. Rev. Lett. 79, 2526–2529 (1997)
[5] B. Rosenow, I. P. Levkivskyi, B. I. Halperin, Phys. Rev. Lett. 116, 156802 (2016).
[6] H. Bartolomei et al. Science 368, 173-177 (2020).
[7] Lee, JY.M., Sim, HS, Nature Communications 13, 6660 (2022).
The communication of plants with their environment is crucial for their survival. Plants are known to use light, odors, and touch to communicate with other organisms, including plants and animals. Yet, acoustic communication is almost unexplored in plants, despite its potential adaptive value. This is the topic of the current talk. We have started exploring plant bioacoustics - what plants hear, and what they “say”. I will describe two major projects: in the first we study plant hearing, testing the responses of flowers to sounds of pollinators; in the second we investigate plant sound emission - we have shown that different species of plants emit brief ultrasonic signals, especially under stress. Using AI we can interpret these sounds and identify plant species and stress condition from the sounds. Potential implications of these projects for plant ecology, evolution and agriculture will be discussed.
The microscopic theory of superconductivity was developed by John Bardeen, Leon N Cooper and J. Robert Schrieffer. It is among the most beautiful and outstanding achievements of modern scientific research. Almost half a century passed between the initial discovery of superconductivity by Kamerlingh Onnes and the theoretical explanation of the phenomenon. During the intervening years the brightest minds in theoretical physics tried and failed to develop a microscopic understanding of the effect. I will discuss some of those unsuccessful attempts to understand superconductivity. This not only demonstrates the extraordinary achievement made by formulating the BCS theory, but also illustrates that mistakes are a natural and healthy part of scientific discourse, and that inapplicable, even incorrect theories can turn out to be interesting and inspiring.
Seminars
Date:
03
March, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
A Statistical Physics Approach to Bacteria under Strong Perturbations
Prof. Nathalie Q. Balaban | Racah Institute of Physics, The Hebrew University
Statistical physics successfully accounts for phenomena involving a large number of components using a probabilistic approach with predictions for collective properties of the system. While biological cells contain a very large number of interacting components, (proteins, RNA molecules, metabolites, etc.), the cellular network is understood as a particular, highly specific, choice of interactions shaped by evolution, and therefore difficultly amenable to a statistical physics description. Here we show that when a cell encounters an acute but non-lethal stress, its perturbed state can be modelled as random network dynamics. Strong perturbations may therefore reveal the dynamics of the underlying network that are amenable to a statistical physics description. We show that our experimental measurements of the recovery dynamics of bacteria from a strong perturbation can be described in the framework of physical aging in disordered systems (Kaplan Y. et al, Nature 2021). Further experiments on gene expression confirm predictions of the model. The predictive description of cells under and after strong perturbations should lead to new ways to fight bacterial infections, as well as the relapse of cancer after treatment.
Seminars
Date:
25
February, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Tails and (boson) peaks in the glassy vibrational density of states
Avraham Moriel | Princeton University - The Department of Mechanical and Aerospace Engineering
Due to their intrinsic nonequilibrium and disordered nature, glasses feature low-frequency, nonphononic vibrations, in addition to phonons. These excess modes generate a peak —the boson peak— in the ratio of the vibrational density of state (VDoS) and Debye’s VDoS of phonons. Yet, the excess vibrations and the boson peak are not fully understood. After presenting the experimental evidence of the boson peak, we will discuss additional universal characteristics of glassy low frequency VDoS obtained through numerical simulations. We will then examine a recently analyzed mean-field model capturing the universal low-frequency glassy VDoS characteristics. Combining reanalyzed experimental data and computer simulations, we will observe that the same mean-field model also captures the origin, nature and properties of the boson peak, yielding a unified physical picture of the low-frequency VDoS spectra of glasses.
FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/
Seminars
Date:
11
February, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Tunable Architecture of Nematic Disclination Lines
In this talk, I introduce a theoretical framework to tailor three-dimensional defect line architecture in nematic liquid crystals. By drawing an analogy between nematic liquid crystals and magnetostatics, I will show quantitative predictions for the connectivity and shape of defect lines in a nematic confined between two thinly spaced glass substrates. I will demonstrate experimental and numerical verification of these predictions, and identify critical parameters that tune the disclination lines' curvature within an experimental setup, as well as non-dimensional parameters that allow matching experiments and simulations at different length scales. Our system provides both physical insight and powerful tools to induce desired shapes and shape changes of defect lines.
Seminars
Date:
04
February, 2024
Sunday
Hour: 13:15-14:30
The Clore Center for Biological Physics
Multiscale Lattice Modeling and Simulations of Heterogeneous Membranes
Prof. Oded Farago | Biomedical Engineering Department, BGU
Mixtures of lipids and cholesterol (Chol) have been served as simple model systems for studying the biophysical principles governing the formation of liquid ordered raft domains in complex biological systems. These mixtures exhibit a rich phase diagram as a function of temperature and composition. Much of the focus in these studies has been given to the coexistence regime between liquid ordered and liquid disordered phases which resembles rafts floating in the sea of disordered lipids. In the talk, I will present a new lattice model of binary [1] and ternary [2, 3] mixtures containing saturated and unsaturated lipids, and Chol. Simulations of mixtures of thousands of lipids and cholesterol molecules on time scales of hundreds of microseconds show a very good agreement with experimental and atomistic simulation observations across multiple scale, ranging from the local distributions of lipids to the macroscopic phase diagram of such mixtures. Importantly, we find that the liquid ordered domains are highly heterogeneous and consist of Chol-poor hexagonally packed gel-like clusters surrounded by Chol-rich regions at the domain boundaries. The presence of such nano-domains within the liquid ordered regions appears as a characteristic feature of the liquid-ordered state, and makes the interpretation of scattering data ambiguous in mixtures not exhibiting macroscopic phase separation.
Seminars
Date:
28
January, 2024
Sunday
Hour: 13:15-14:15
The Clore Center for Biological Physics
Some organizing principles behind microbial community dynamics
Microbial ecosystems, pivotal in global ecological stability, display a diverse array of species, influenced by complex interactions. When considering environments with changing nutrient levels, we have recently suggested an 'early bird' effect. This phenomenon, which results from changing nutrient levels, initial and fast uptake of resources confers an advantage, significantly altering microbial growth dynamics. In serial dilution cultures with varying nutrient levels, this effect leads to shifts in diversity, demonstrating that microbial communities do not adhere to a universal nutrient-diversity relationship. Using a consumer-resource, serial dilution modeling framework, we simulate scenarios of changing nutrient balance, such as variations in phosphorous availability in rainforest soils, to predict a possible lag in ecosystems response near a loss of diversity transition point. Lastly, we explore the notion of 'microbial debt', a form of the early bird advantage, where microbes initially grow rapidly at the cost of later growth or increased mortality. This dynamic, exemplified in both classical chemostat and serial dilution cultures, reveals that such debt can convey an advantage, with varying outcomes on community structure depending on the nature of the trade-off involved. Together, these studies illuminate some organizing principles behind microbial dynamics, balancing growth and survival in changing environments.
Seminars
Date:
21
January, 2024
Sunday
Hour: 13:15-14:15
The Clore Center for Biological Physics
How informative are structures of dna-bound proteins for revealing binding mechanisms inside cells? the case of the Origin of Replication Complex (ORC)
The Origin Recognition Complex (ORC) seeds the replication-fork by binding DNA replication origins, which in budding yeast contain a 17bp DNA motif. High resolution structure of the ORC-DNA complex revealed two base-interacting elements: a disordered basic patch (Orc1-BP4) and an insertion helix (Orc4-IH).
To define ORC elements guiding its DNA binding in-vivo, we mapped genomic locations of 38 designed ORC mutants. We revealed that different ORC elements guide binding at different motifs sites, and these correspond only partially to the structure- described interactions. In particular, we show that disordered basic patches are key for ORC-motif binding in-vivo, including one lacking from the structure. Finally i will discuss how those disordered elements, which insert into the minor-groove can still guide specific ORC-DNA recognition.
The kinetics of protein–DNA recognition, along with its thermodynamic properties, including affinity and specificity, play a central role in shaping biological function. Protein–DNA recognition kinetics are characterized by two key elements: the time taken to locate the target site amid various nonspecific alternatives; and the kinetics involved in the recognition process, which may necessitate overcoming an energetic barrier. In my presentation, I will describe the complexity of protein-DNA kinetics obtained from molecular coarse-grained simulations of various protein systems. The kinetics of protein-DNA recognition are influenced by various molecular characteristics, frequently necessitating a balance between kinetics and stability. Furthermore, protein-DNA recognition may undergo evolutionary optimization to accomplish optimal kinetics for ensuring proper cellular function.
Seminars
Date:
09
January, 2024
Tuesday
Hour: 12:45-13:45
Special Clore Seminar - Leenoy Meshulam
Bridging scales in biological systems – from octopus skin to mouse brain
For an animal to perform any function, millions of cells in its body furiously interact with each other. Be it a simple computation or a complex behavior, all biological functions involve the concerted activity of many individual units. A theory of function must specify how to bridge different levels of description at different scales. For example, to predict the weather, it is theoretically irrelevant to follow the velocities of every molecule of air. Instead, we use coarser quantities of aggregated motion of many molecules, e.g., pressure fields. Statistical physics provides us with a theoretical framework to specify principled methods to systematically ‘move’ between descriptions of microscale quantities (air molecules) to macroscale ones (pressure fields). Can we hypothesize equivalent frameworks in living systems? How can we use descriptions at the level of cells and their connections to make precise predictions of complex phenomena My research group will develop theory, modeling and analysis for a comparative approach to discover generalizable forms of scale bridging across species and behavioral functions. In this talk, I will present lines of previous, ongoing, and proposed research that highlight the potential of this vision. I shall focus on two seemingly very different systems: mouse brain neural activity patterns, and octopus skin cells activity patterns. In the mouse, we reveal striking scaling behavior and hallmarks of a renormalization group- like fixed point governing the system. In the octopus, camouflage skin pattern activity is reliably confined to a (quasi-) defined dynamical space. Finally, I will touch upon the benefits of comparing across animals to extract principles of multiscale function in biological systems, and propose future directions to investigate how macroscale properties, such as memory or camouflage, emerge from microscale level activity of individual cells.
Seminars
Date:
07
January, 2024
Sunday
Hour: 13:15-14:15
Clore Seminar-Professor Jay Fineberg
The Fundamental Physics of the Onset of Frictional Motion: How do laboratory earthquakes nucleate?
Recent experiments have demonstrated that rapid rupture fronts, akin to earthquakes, mediate the transition to frictional motion. Moreover, once these dynamic rupture fronts (“laboratory earthquakes”) are created, their singular form, dynamics and arrest are well-described by fracture mechanics. Ruptures, however, need to be created within initially rough frictional interfaces, before they are able to propagate. This is the reason that “static friction coefficients” are not well-defined; frictional ruptures can nucleate for a wide range of applied forces. A critical open question is, therefore, how the nucleation of rupture fronts actually takes place. We experimentally demonstrate that rupture front nucleation is prefaced by extremely slow, aseismic, nucleation fronts. These nucleation fronts, which are often self-similar, are not described by our current understanding of fracture mechanics. The nucleation fronts emerge from initially rough frictional interfaces at well-defined stress thresholds, evolve at characteristic velocity and time scales governed by stress levels, and propagate within a frictional interface to form the initial rupture from which fracture mechanics take over. These results are of fundamental importance to questions ranging from earthquake nucleation and prediction to processes governing material failure.
Seminars
Date:
31
December, 2023
Sunday
Hour: 13:15-14:15
The Clore Center for Biological Physics
Erasing information fast and cheap --- How to approach Landauer’s bound?
The celebrated Landauer bound is the fundamental universal cost of computation: there must be dissipation of at least kBTlog2 per erasure of one bit. This fundamental bound is reached when the erasure protocol is performed in the slow quasi-static limit. Generally, the faster the erasure protocol, the more dissipation is generated.
In this talk, I will present two approaches that challenge this view. First, it will be shown that by the use of a conserved quantity in the system, one can bypass Liouville’s theorem and perform erasure at zero energetic cost. The second approach that will be discussed is considering a system that is weakly coupled to the environment. In that case, one can design an erasure procedure that does not scale with its operation time.
We are building a new ground-based observatory in Neot Smadar, located in the south of the Negev desert.
One of the telescopes hosted at this site is the Large Array Survey Telescope (LAST). LAST is a cost-effective survey telescope capable of quickly
scanning the sky and studying the dynamic sky, from solar system objects to explosions at cosmological distances.
I will describe the Neot Smadar site, the LAST system, and some of the science cases for which LAST was built.
I will describe an attempt to describe turbulence using the methods of quantum field theory. We consider waves that interact via four-wave scattering (such as sea waves, plasma waves, spin waves, and many others). By summing the series of the most UV-divergent terms in the perturbation theory, we show that the true dimensionless coupling is different from the naive estimate, and find that the effective interaction either decays or grows explosively with the cascade extent, depending on the sign of the new coupling. The explosive growth possibly signals the appearance of a multi-wave bound state (solitons, shocks, cusps) similar to confinement in quantum chromodynamics.
Colloquia
Date:
07
September, 2023
Thursday
Hour: 11:15-12:30
Physics colloquium
What Is the Next Milestone for High-Energy Particle Colliders?
The CERN Large Hadron Collider (LHC) has discovered the Higgs boson and confirmed the predictions for many of its properties given by the "Standard Model" of particle physics. However, this does not mean that particle physics is solved. Mysteries that the Standard Model does not address are still with us and, indeed, stand out more sharply than ever. To understand these mysteries, we need experiments at still higher energies. In this colloquium, I will argue that we should be planning for a particle collider reaching energies of about 10 times those of the LHC in the collisions of elementary particles. Today, there is no technology that can produce such energies robustly and at a reasonable cost. However, many solutions are under study, including colliders for protons, muons, electrons, and photons. I will review the status of these approaches to the design of the next great energy-frontier accelerator.
The intercalation of ions is a powerful strategy to modify the structural, electrical and optical properties of layered solids [1]. It is also a key ingredient for energy storage and the operation of secondary batteries. Even though first studies of driving chemical elements into the van der Waals galleries of graphite date back to as early as 1840, we believe that our recent successful demonstration of on-chip electrochemistry driven ion intercalation in the single van der Waals gallery of a graphene bilayer marks a paradigm shift. The “active” device area is left uncovered by the electrolyte and we can borrow the toolbox of the low dimensional electron system community for monitoring the ion transport [2,3]. This intercalation 2.0 offers, in conjunction with the versatile technique of van der Waals stacking of 2D materials for engineering arbitrary layered structures and hetero-interfaces, unprecedented control and truly unique opportunities to chart new territory in the fields addressing ion transport, diffusion, storage and intercalant induced structural, electronic and optical property changes. Here, examples will be presented how this technique has been exploited to study ion diffusion, ion ordering as well as unconventional superconductivity.
[1] M.S. Dresselhaus, G. Dresselhaus, Intercalation compounds of graphite, Advances in Physics 51-1, 1-186 (2002).
[2] M. Kühne, F. Paolucci, J. Popovic, P. Ostrovsky, J. Maier, J. Smet, Ultrafast lithium diffusion in bilayer graphene, Nature Nanotechnology 12, 895 (2017).
[3] M. Kühne, F. Börrnert, S. Fecher, M. Ghorbani-Asl, J. Biskupek, D. Samuelis, A. Krasheninnikov, U. Kaiser, J. Smet, Reversible superdense ordering of lithium between two graphene sheets, Nature 564, 234-239 (2018).
Connecting theoretical models for exotic quantum states to real materials is a key goal in quantum materials science. The structure of the crystalline lattice plays a foundational role in this pursuit in the subfield of quantum material synthesis. We here revisit this long-standing perspective in the context low dimensional emergent electronic phases of matter. In particular, we discuss recent progress in realizing new lattice and superlattice motifs designed to address model topological and correlated electronic phenomena. We comment on the perspective for realizing further 2D model systems in complex material structures and connections to further paradigms for programmable quantum matter.
Colloquia
Date:
26
June, 2023
Monday
Hour: 11:15-12:30
Physics colloquium
Quantum control of dynamical states with switching times exceeding ten seconds
Macroscopic switching times between two stable states are widespread in science and engineering. Common examples are the reversal of earth's magnetic field, or bit-flips in computer memories. Remarkably, long switching times persist even in systems at wildly reduced scales, such as oscillators containing only a handful of photons. Despite far reaching implications in quantum information science, preparing and measuring quantum superpositions of long-lived dynamical states has remained out of reach. Previous attempts achieved quantum control by introducing ancillary systems that in turn propagated errors limiting the switching times in the millisecond range. In this work, we implement a bistable dynamical system in a nonlinearly dissipative superconducting oscillator with an embedded parametric tool for quantum control and tomography. Through direct Wigner tomography, we observe quantum superpositions of dynamical states with switching times up to twenty seconds. Using quantum Zeno dynamics, we control the phase of these superpositions, and observe coherent oscillations decaying on the scale of hundreds of nanoseconds. This experiment demonstrates the encoding of quantum information in macroscopically stable dynamical states, promising shortcuts in the emergence of quantum technologies.
Refs : Leghtas et al. Science 347, 853 (2015). Lescanne et al. Nature Physics 16, 509 (2020). Berdou et al. PRX Quantum preprint arXiv:2204.09128.
The discovery of planets capable of hosting biosignatures, and the characterization of the atmospheres of these planets, is a key and achievable goal in our lifetime. These goals require some of the most demanding precision spectroscopic and photometric measurements. I will discuss the instrumental challenges of detecting such planets with the Doppler radial velocity technique, and the evolution of the design of these instruments as they seek ever-tighter control of environmental parameters, and increased measurement precision. A suite of new technologies like frequency stabilized laser combs, low drift etalons, and deeper understanding of the detectors is enabling a new level of precision in radial velocity measurements - as well as illustrating new challenges. I will then discuss how the stars themselves are the remaining challenge, as magnetically driven processes create ‘stellar activity’ noise that can masquerade as planets and obfuscate their detection, and I highlight a few paths to mitigate this, along with some of the latest scientific results from the HPF and NEID instruments. I will discuss one iteration of a possible future, weaving its way from now through JWST individual and mini-population studies of planet atmospheres, large population studies with missions like ARIEL, the near-future of RV surveys, detection and characterization prospects with large ground-based, and the challenges and opportunities with future imaging and spectroscopic missions like LUVOIR and LIFE. The goal of discovering and characterizing terrestrial mass planets capable of hosting liquid water on their surfaces may now be within reach! But true understanding of the origin and meaning of the biosignatures we detect will likely require transdisciplinary research across multiple fields.
Colloquia
Date:
15
June, 2023
Thursday
Hour: 11:15-12:30
Physics Colloquium
Search for quantum applications and taking POCs to production
The Amazon Quantum Solutions Lab works closely with enterprise customers to identify use cases where quantum technologies might have impact in the fault-tolerant future, but also to develop creative ways to solve complex business challenges at scale today. In this presentation, I will showcase selected customer use cases and discuss where and when quantum machines can have an impact.
Colloquia
Date:
01
June, 2023
Thursday
Hour: 11:15-12:30
Physics Colloquium
Elastic Strain Engineering for Unprecedented Properties
The emergence of “ultra-strength materials” that can withstand significant fractions of the ideal strength at component scale without any inelastic relaxation harbingers a new field within mechanics of materials. Recently, we have experimentally achieved more than 13% reversible tensile strains in Si that fundamentally redefines what it means to be Si, and ~7% uniform tensile strain in micron-scale single-crystalline diamond bridge arrays, where thousands of transistors and quantum sensors can be integrated in one diamond microbridge. Elastic Strain Engineering (ESE) aims to endow material structures with very large stresses and stress gradients to guide electronic, photonic, and spin excitations and control energy, mass, and information flows. As “smaller is stronger” for most engineering materials at room temperature, a much larger dynamical range of tensile-and-shear deviatoric stresses for small-scale structures can be achieved, as the defect (e.g., dislocation, crack) population dynamics change from defect-propagation to defect-nucleation controlled. Thus, all six stress components can be used to tune the physical and chemical properties of a material like a 7-element alloy. Four pillars of ESE need to be addressed experimentally and computationally: (a) making materials and structures that can withstand deviatoric elastic strain patterns that are exceptionally large and extended in space-time volume, inhomogeneous, dynamically reversible, or combinations thereof, (b) measuring and understanding how functional properties such as photonic and electronic characteristics vary with imposed elastic strain tensor, (c) characterizing and modeling the mechanisms of stress relaxations; the goal is not to use them for forming but to defeat them at service temperatures (usually room temperature and above) and extended timescales, and (d) computational design based on first principles, e.g. predicting ideal strength surface, topological changes in band structures, etc. assisted by machine learning.
A central goal of physics is to
understand the low-energy solutions of
quantum interactions between
particles. This talk will focus on the
complexity of describing low-energy
solutions; I will show that we can
construct quantum systems for which
the low-energy solutions are highly
complex and unlikely to exhibit succinct
classical descriptions. I will discuss the
implications these results have for robust
entanglement at constant temperature and the
quantum PCP conjecture. En route, I will
discuss our positive resolution of the No Lowenergy
Trivial States (NLTS) conjecture on the
existence of robust complex entanglement.
Mathematically, for an n-particle system, the
low-energy states are the eigenvectors
corresponding to small eigenvalues of an
exp(n)-sized matrix called the Hamiltonian,
which describes the interactions between the
particles. Low-energy states can be thought of
as approximate solutions to the local
Hamiltonian problem with ground-states
serving as the exact solutions. In this sense,
low-energy states are the quantum
generalizations of approximate solutions to
satisfiability problems, a central object of
study in theoretical computer science. I will
discuss the theoretical computer science
techniques used to prove circuit lower bounds
for all low-energy states. This morally
demonstrates the existence of Hamiltonian
systems whose entire low-energy subspace is
robustly entangled.
I will describe some of our recent work re-analyzing the gravitational wave data made public by the LIGO collaboration. More broadly I will discuss some of the outstanding questions related to binary black hole mergers and what the data might be saying about how the GW sources formed. I will comment on some fruitful directions for further improvements.
Colloquia
Date:
09
May, 2023
Tuesday
Hour: 11:00-12:30
Physics Colloquium
Intense Laser-Material Interactions: Stars, Exoplanets, and Unique States of Matter in the
Laboratory
Since 1970, the University of Rochester and other laboratories around the world have
built more energetic and more powerful lasers. These technology advances have enabled new
science regimes. Fifty years later, fusion ignition has been achieved in the laboratory ,
where more energy than the laser energy was released ; an amazing demonstration of precision
science under extreme conditions.Astrophysics is now a laboratory science-new equations of
state, constitutive properties and structures are measured at conditions equivalent to giant gas
planets and super earths. Ultrashort pulse lasers, a LLE invention acknowledged in the 2018
Nobel Prize for Physics, is enabling ultrahigh field physics and new generations of particle
accelerators and light sources. Recent progress on ignition, high-energy-density science and
short-pulse laser physics will be summarized. The pursuit of direct-drive fusion and the path
to 25 Petawatt lasers will be discussed.
Statistical physics has a bad track record in describing large-N gravitational systems.
It has become clear over the last several years that there is a remarkable exception
to this rule. Resonant relaxation due to orbit-averaged secular dynamics in galactic nuclei
drives them to states of thermal and rotational equilibria on an astronomically short timescale.
There are fun applications: phase transitions leading to lopsided precessing equilibria (similar-looking to the nucleus of Andromeda), and strong clustering in eccentricity and inclination of stellar-mass black holes. Following Rauch and Tremaine, I will use statistical physics to argue that secular-dynamical "resonant friction" must exist and
that moreover, it likely plays a huge role in galactic nuclei. It controls the dynamics of Intermediate-Mass Black Holes as well
as that of stellar and accretion discs. The young stellar disc at the center of our Galaxy presents a good case study for this effect.
Quantum technologies allow for fully novel schemes of hybrid computing. We
employ modern segmented ion traps. I will sketch architectures, the required trap
technologies and fabrication methods, control electronics for quantum register
reconfigurations, and recent improvements of qubit coherence and gate
performance. Currently gate fidelities of 99.995% (single bit) and 99.8% (two bit) are
reached. We are implementing a reconfigurable qubit register and have realized
multi-qubit entanglement [1] and fault-tolerant syndrome readout [2] in view for
topological quantum error correction [3] and realize user access to quantum
computing [4]. The setup allows for mid-circuit measurements and real-time control
of the algorithm. We are currently investigating various used cases, including
variational quantum eigensolver approaches for chemistry or high energy relevant
models, and measurement-based quantum computing. The fully equipped in house
clean room facilities for selective laser etching of glass enables us to design and
fabricate complex ion trap devices, in order to scale up the number of fully
connected qubits. Also, we aim for improving on the speed of entanglement
generation. The unique and exotic properties of ions in Rydberg states [5] are
explored experimentally, staring with spectroscopy [6] of nS and nD states where
states with principal quantum number n=65 are observed. The high polarizability [7]
of such Rydberg ions should enable sub-μs gate times [8].
[1] Kaufmann er al, Phys. Rev. Lett. 119, 150503 (2017)
[2] Hilder, et al., Phys. Rev. X.12.011032 (2022)
[3] Bermudez, et al, Phys. Rev. X 7, 041061 (2017)
[4] https://iquan.physik.uni-mainz.de/
[5] A. Mokhberi, M. Hennrich, F. Schmidt-Kaler, Trapped Rydberg
ions: a new platform for quantum information processing,
Advances In Atomic, Molecular, and Optical Physics, Academic
Press, Ch. 4, 69 (2020), arXiv:2003.08891
[6] Andrijauskas et al, Phys. Rev. Lett. 127, 203001 (2021)
[7] Niederlander et al, NJP 25 033020 (2023)
[8] Vogel et al, Phys. Rev. Lett. 123, 153603 (2019)
Abstract: Around the world, several groups are working to detect very
low frequency gravitational waves using "pulsar timing arrays". The
gravitational waves are generated by orbiting pairs of extremely
massive black holes at cosmological distances from Earth. The
"detector" operates at a Galactic-scale, exploiting radio pulsars
(very stable rapidly-spinning neutron stars) as high precision clocks.
I'll explain how these detectors operate -- the gravitational waves
leave detectable imprints on the radio pulses -- and review the
current state of the field and its prospects. I'll also describe some
recent work (arXiv:2205.05637, arXiv:2208.07230) on the "Hellings and
Downs correlation". This pattern of pulsar timing correlations is the
"smoking gun" that should reveal the presence of gravitational waves.
Understanding quantum channels and the strange behavior of their capacities is a key driver of quantum information theory. Despite having rigorous coding theorems, quantum capacities are poorly understood due to super-additivity effects. We will talk about a remarkably simple, low-dimensional, single-parameter family of quantum channels with exotic quantum information-theoretic features. As the simplest example from this family, we focus on a qutrit-to-qutrit channel that is intuitively obtained by hybridizing together a simple degradable channel and a completely useless qubit channel. Such hybridizing makes this channel's capacities behave in a variety of interesting ways. For instance, the private and classical capacity of this channel coincide and can be explicitly calculated, even though the channel does not belong to any class for which the underlying information quantities are known to be additive. Moreover, the quantum capacity of the channel can be computed explicitly, given a clear and compelling conjecture is true. This "spin alignment conjecture," which may be of independent interest, is proved in certain special cases and additional numerical evidence for its validity is provided. We further show that this qutrit channel demonstrates superadditivity when transmitting quantum information jointly with a variety of assisting channels, in a manner unknown before. A higher-dimensional variant of this qutrit channel displays super-additivity of quantum capacity together with an erasure channel. Subject to the spin-alignment conjecture, our results on super-additivity of quantum capacity extend to lower-dimensional channels as well as larger parameter ranges. In particular, super-additivity occurs between two weakly additive channels each with large capacity on their own, in stark contrast to previous results. Remarkably, a single, novel transmission strategy achieves super-additivity in all examples. Our results show that super-additivity is much more prevalent than previously thought. It can occur across a wide variety of channels, even when both participating channels have large quantum capacity.
This is joint work with Debbie Leung, Vikesh Siddhu, Graeme Smith, and John Smolin, and based on the papers https://arxiv.org/abs/2202.08380 and https://arxiv.org/abs/2202.08377.
Seminars
Date:
06
March, 2023
Monday
Hour: 11:00-12:00
Tensor networks, fundamental theorems, and complexity
Tensor networks describe high-dimensional tensors succinctly, in terms of a network or graph of local data. Many interesting tensors arise in this way -- from many-body quantum states in physics to the matrix multiplication tensors in algebraic complexity. While widely successful, the structure of tensor networks is still only partially understood. In this talk, I will give a gentle introduction to tensor networks and explain some recent advances in their theory. In particular, we will discuss the significance of the so-called “fundamental theorem”, which is at the heart of much of the success of tensor networks, and explain how to generalize it to higher dimensions. Before our work, "no go" results suggested that such a generalization might not exist!! Along the way, we will see how to turn an undecidable problem into one that admits an algorithmic solution. To achieve this we draw on recent progress in theoretical computer science and geometric invariant theory.
Colloquia
Date:
26
February, 2023
Sunday
Hour: 16:15-18:00
Physics Colloquium
Lasing without inversion during laser filamentation in the air
Lasing during laser filamentation in the air was discovered about a decade ago. Its physical origins remain puzzling and controversial to this day. Yet, the phenomenon itself appears stubbornly robust and ubiquitous, arising experimentally under many different conditions.
In this talk I will argue that air lasing is a spectacular manifestation of lasing without inversion. In contrast to a frequent belief that lasing without inversion is a delicate, exotic, and fragile phenomenon,
this particular incarnation of it appears as inevitable and as robust as the simple fact that short intense laser pulses inevitably force nitrogen molecules in the air to align, ionize, and continue to rotate after the laser pulse is gone.
I will also point out how one can tailor the initial laser pulse to turn air lasing into lasing with real inversion. The implication is that once you fire your tailored laser pulse sequence into the air, the air might actually fire back at you, within a picosecond or so.
Seminars
Date:
22
February, 2023
Wednesday
Hour: 11:00-12:00
Strong light-exciton interactions in 2D semiconductors
Prof. Itai Epstein | School of electrical engineering, TAU
The remarkable properties of excitons in transition-metal-dichalcogenides (TMDs), together with the ability to readily control their charge carriers, have attracted a significant amount of interest in recent years. Despite the atomic dimensions of the hosting 2D semiconductors, TMD excitons exhibit strong interaction with light, both in absorption and photoemission processes, and practically dominate the optical response of these 2D materials. In this talk, I will introduce several approaches for achieving extremely strong light-exciton interactions. First, by optical and electrical manipulation of TMD excitons inside a van der Waals heterostructure cavity [1], second, via the formation of highly-confined, in-plane exciton polaritons [2], and third, through the realization of valley-polarized hyperbolic exciton polaritons [3].
These enhanced light–exciton interactions may provide a platform for studying excitonic phase-transitions, quantum nonlinearities and the enablement of new possibilities for 2D semiconductor-based optoelectronic devices.
[1] I. Epstein et al, "Near-unity Light Absorption in a Monolayer WS2 Van der Waals Heterostructure Cavity", Nano letters 20 (5), 3545-3552 (2020).
[2] I. Epstein et al, "Highly Confined In-plane Propagating Exciton-Polaritons on Monolayer Semiconductors", 2D Materials 7, 035031 (2020).
[3] T. Eini, T. Asherov, Y. Mazor, and I. Epstein, "Valley-polarized Hyperbolic Exciton Polaritons in Multilayer 2D Semiconductors at Visible Frequencies", Phys. Rev. B 106, L201405 (2022).
Colloquia
Date:
19
February, 2023
Sunday
Hour: 11:15-12:30
Physics Colloquium
New Avenues in Quantum Computing: Beyond Quantum Circuits with Trapped-Ion Qubits
Trapped ions are a leading quantum technology for quantum computation and simulation, with the capability to solve computationally hard problems and deepen our understanding of complex quantum systems. The quantum circuit model is the central paradigm for quantum computation, enabling the realization of various quantum algorithms by application of multiple one- and two-qubit entangling operations. However, the typical number of entangling operations required by this model increases exponentially with the number of qubits, making it difficult to apply to many problems.
In my presentation, I will discuss new methods for realizing quantum gates and simulations that go beyond the quantum circuit model. I will first describe a single-step protocol for generating native, -body interactions between trapped-ion spins, using spin-dependent squeezing. Next, I will present a preparation of novel phases of matter using simultaneous and reconfigurable spin-spin interactions. Lastly, I will explore new avenues to harness the long-lived phonon modes in trapped-ion crystals for simulating complex bosonic and spin-boson models that are difficult to solve using classical methods. The presented techniques could push the performance of trapped-ion systems to solve problems that are currently beyond their reach.
How can we convey a complex idea - a technology, theory, product or initiative - in a clear, fascinating and effective way?
This is a question that thousands of professors, teachers and engineers wrestle with every time they need to present or teach a complex idea. Fortunately, the same proven techniques that have been used by generations of writers, playwrights and directors - come to our aid even in the twenty-first century.
In the lecture we will talk about:
- How to get inside the view's head,
- How to identify vital or redundant pieces of information,
- How to strengthen our presentation by using ideas that contradict and even oppose our ideas! and much more.
The electronic properties of a material are dictated by both the composition and arrangement of its atomic lattice. Combining elemental atoms selected from the periodic table in principle provides for infinite variety of materials to be realized. However, thermodynamic constraints limit which atoms may bond into which symmetry classes; materials may or may not be air sensitive; synthesis conditions may be impractical; impurities and defects may substantially obscure intrinsic electronic properties; and the resulting electron behaviour may not be predictive owing to phenomena such as strong electron interactions, spontaneous magnetic ordering, fermi-surface reconstruction or other effects not captured by single-particle band-structure calculations. In this talk, I will explore new approaches to synthesizing quantum materials by augmenting the atomic lattice structure in 2D materials with a superimposed superlattice potential. Artificially engineering lattice potentials provide opportunities to synthesize materials beyond the periodic table, with the ultimate promise to be able to realize and manipulate arbitrary electronic states, by design. Opportunities and challenges, in this exciting new field will be reviewed, and the prospects for quantum simulation in a solid-state platform will be discussed.
This talk will present our recent work on the use of arrays of Rydberg atoms to study
quantum magnetism and to generate entangled states useful for quantum metrology. We
rely on laser-cooled ensembles of up to hundred individual atoms trapped in microscopic
optical tweezer arrays. By exciting the atoms into Rydberg states, we make them interact by
the resonant dipole interaction. The system thus implements the XY spin ½ model, which
exhibits various magnetic orders depending on the ferromagnetic or antiferromagnetic
nature of the interaction. In particular, we adiabatically prepare long-range ferromagnetic
order. When the system is placed out of equilibrium, the interactions generate spin squeezing. We characterize the degree of squeezing and observe that it scales with the number of atoms.
Seminars
Date:
19
January, 2023
Thursday
Hour: 16:00-18:00
Collective light scattering in cold atomic ensembles: super-radiance & driven Dicke model
Collective light scattering in cold atomic ensembles: super-radiance & driven Dicke model
This talk will present our recent work on the observation of super-radiance in a cloud of cold
atoms and the implementation of the driven Dicke model in free space. We start from an
elongated cloud of laser cooled atoms that we excite either perpendicularly or along its
main axis. This situation bears some similarities with cavity quantum electrodynamics: here
the cavity mode is replaced by the diffraction mode of the elongated cloud. We observe
superradiant pulses of light after population inversion. When exciting the cloud along the
main axis, we observe the Dicke super-radiant phase transition predicted 40 years ago and
never observed in free space. We also measure the statistics of the emitted light and find
that it has the properties predicted for a super-radiant laser.
The recent breakthrough in the detection of gravitational waves (GWs)
from merging black hole (BH) and neutron star (NS) binaries by
advanced LIGO/Virgo has generated renewed interest in understanding
the formation mechanisms of merging compact binaries, from the
evolution of massive stellar binaries and triples in the galactic
fields, dynamical interactions in dense star clusters to binary
mergers in AGN disks. I will review these different formation
channels, and discuss how observations of spin-orbit misalignments,
eccentricities, masses and mass ratios in a sample of merging binaries
by aLIGO can constrain various formation channels. The important roles
of space-borne gravitational wave detectors (LISA, TianQin, Taiji etc)
will also be discussed.
Colloquia
Date:
12
January, 2023
Thursday
Hour: 11:15-12:30
Physics Colloquium
How crystals flow - plastic deformation of colloidal single crystals
Plastic (irreversible) deformation of crystals requires disrupting the crystalline order, which happens through nucleation and motion of topological line defects called dislocations. Interactions between dislocations lead to the formation of complex networks that, in turn, dictate the mechanical response of the crystal. The severe difficulty in atomic systems to simultaneously resolve the emerging macroscopic deformation and the evolution of these networks impedes our understanding of crystal plasticity. To circumvent this difficulty, we explore crystal plasticity by using colloidal crystals; the micrometer size of the particles allows us to visualize the deformation process in real-time and on the single particle level.
In this talk, I will focus on two classical problems: instability of epitaxial growth and strain hardening of single crystals. In direct analogy to epitaxially grown atomic thin films, we show that colloidal crystals grown on mismatched templates to a critical thickness relax the imposed strain by nucleation of dislocations. Our experiments reveal how interactions between dislocations lead to an unexpectedly sharp relaxation process. I will then show that colloidal crystals can be strain-hardened by plastic shear; the yield strength increases with the dislocation density in excellent accord with the classical Taylor equation, originally developed for atomic crystals. Our experiments reveal the underlying mechanism for Taylor hardening and the conditions under which this mechanism fails.
Colloquia
Date:
10
January, 2023
Tuesday
Hour: 16:15-18:00
Special Physics Colloquium
Quantum Simulation: from many to few body problems.
Many-body quantum systems are very difficult to simulate with classical computers, as the computational resources (time and memory) usually grow exponentially
with the size of the system. However, quantum computers and analog quantum simulators can perform that task much more efficiently. In this talk, I will first review some of
the quantum algorithms that have been proposed to simulate dynamics, prepare ground states, or compute physical properties at finite temperatures. I will then focus on analog quantum simulation with cold atoms in optical lattices and describe methods for tackling physics and chemistry problems with such a system.
Seminars
Date:
09
January, 2023
Monday
Hour: 14:30-15:30
Quantum metrology for various applications and platforms
The field of quantum metrology seeks to develop quantum protocols to enhance the precision of measurements with applications ranging from NMR and gravimeters to calibration of quantum devices. The general tools and bounds of quantum metrology assume perfect detection. However, the detection in most quantum experimental platforms is noisy and imperfect. We fill this gap and develop a theory that takes into account general measurements . We generalize the precision bounds to account for arbitrary detection channels. We find the general form of the precision bounds and of the optimal control for pure states. We then consider quantum states in a multi-partite system and study the impact of detection noise on quantum enhancement in sensitivity. Interestingly, the achievable sensitivity depends crucially on the allowed control operations. For local optimal control, the detection noise severely degrades the sensitivity and limits any quantum enhancement to a constant factor. On the other hand, with optimal global control the detection noise can be completely removed, and the noiseless sensitivity bounds can be retrieved for a generic class of quantum states (including all pure
states and symmetric states).
Low-mass galaxies provide an essential testing ground for theoretical predictions of cosmology. Their number densities, structures, and internal dynamics provide some of the most interesting clues to the nature of dark matter and the theory of galaxy formation on small scales. Recent advances in telescope instrumentation and image analysis techniques have enabled comprehensive investigations of such low surface brightness galaxies. I will present results from novel observations of low-mass galaxies beyond our local galactic neighborhood, uncovering their significant diverseness and new astrophysical puzzles. I will discuss some of the follow-up observations of these extragalactic low-mass galaxies, focusing on their dark matter content and intriguing globular cluster populations. I will conclude by briefly discussing ongoing and future surveys that collectively have the potential to unveil the physics of dark matter.
Colloquia
Date:
15
December, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid Colloquium
Review of high energy density physics driven by advanced pulsed-power systems
Pulsed power accelerators compress electrical energy in space and time to provide versatile experimental platforms for high energy density and inertial confinement fusion science. The 80-TW “Z” pulsed power facility at Sandia National Laboratories is the largest pulsed power device in the world today. Z discharges up to 22 MJ of energy stored in its capacitor banks into a current pulse that rises in 100 ns and peaks at a current as high as 30 MA in mm-scale targets. Considerable progress has been made over the last decade in the use of pulsed power as a precision scientific tool and for achieving extremely high-energy-density conditions. This talk reviews fundamental science research at Sandia in inertial confinement fusion, dynamic high-pressure material science, intense x-ray radiation science, and pulsed power technology. I will conclude with a few remarks on a Next Generation Pulsed Power project that the U.S. government is considering at this time. Comments will be given on the last-week announcement on the “major scientific breakthrough in Fusion ignition”.
Our organs and tissues are made of different cell types that communicate with each other in order to achieve joint functions. However, little is known about the universal principles of these interactions. For example, how do cell interactions maintain stable cell composition, spatial organization and collective division of labor in tissues?
And what is the role of these interactions in tissue-level diseases where the healthy balance in the tissue is disrupted such as excess scarring following injury known as fibrosis? In this talk, I will discuss my work in developing new theoretical frameworks that explore the collective behavior of cells that emerges from cell-cell interactions.
I will present work on the cell communication circuit that controls tissue repair following injury and how it may lead to fibrosis. I will discuss a new mathematical approach to explore how cell interactions can be used to provide symmetry breaking and optimal division of labor in tissues, and how this approach can help to interpret complex patterns in real high-dimensional data.
I will introduce a new concept in complex networks – network hyper-motifs, where we explore how small recurring patterns (network motifs) are integrated within large networks, and how these larger patterns (hyper-motifs) can give rise to emergent dynamic properties. Finally, I will conclude with future directions that are aimed at revealing principles that unify our understanding of different tissues.
Colloquia
Date:
24
November, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid Colloquium
Fractionalized quantum states of matter through the duality lens
The building blocks of condensed matter systems are just humble electrons. Still, their excitations may carry fractional quantum numbers or obey exchange statistics that are neither bosonic nor fermionic. An essential question is how to ‘get fractions by combining integers’ and what prompts a microscopic system to do so. I will introduce the basic mechanism behind such fractionalization and describe two examples where it arises in nature. The first is the fractional quantum Hall effect, where I will explain how topologically protected neutral modes can be detected via pure charge-conductance measurements. I will then discuss the phenomenon of spin-charge separation and use field-theoretic dualities to construct concrete models where it occurs.
Type Ia supernovae are fundamental phenomena in nature. They are one of the leading
distributors of heavy chemical elements and, in some cases, important production sites (e.g., iron). Type Ia supernovae are very homogenous and bright, allowing their distance to be measured on cosmological scales.
In recent years, measurements of Type Ia supernovae have led to the discovery that the universe's expansion is
accelerating, suggesting the existence of dark energy. Type Ia supernovae are likely thermonuclear explosions
of white-dwarf stars, which are sufficiently dense to allow explosive thermonuclear burning if adequately ignited. However, a robust comparison of theoretical scenarios for the progenitor systems to observations is challenging due to the inability to accurately calculate the dynamics of the explosion and the emitted radiation. We have developed novel observational and numerical methods by exploiting the physical principles behind Type Ia supernovae. The new observational techniques allow the derivation of a specific luminosity-width correlation that does not require radiation transfer calculations for comparison. The new numerical methods allow for the first time to calculate this luminosity-width correlation with a percent accuracy for multidimensional
progenitor scenarios with current computational facilities. We show that all known Type Ia supernova models fail to
reproduce the observed luminosity-width correlation.
despite hundreds of searches for physics beyond the standard model (BSM),
and hundreds of person years invested, no confirmed deviation from the standard model (SM) has been observed. Yet, the LHC data is far from being fully explored and BSM physics could be easily hidden in the already collected data. This calls for the development of new search approaches and methods. The Data Directed Paradigm (DDP) presented in this talk is one possible approach. While the DDP can be implemented exploiting different properties of the SM, here we discuss its implementation for symmetries of the SM and demonstrate its performance relative to traditional searches for lepton flavor violation and lepton non universality.
Colloquia
Date:
07
November, 2022
Monday
Hour: 10:00-11:15
Special Clore Colloquium
Single molecular tracking of vesicle transport neurons and new insights in biophysics, molecular biology and non-thermal equilibrium statistical physics
The historic discovery of gravitational waves by LIGO has initiated a new era of astronomy, permitting us to observe the universe through new eyes. LIGO is sensitive to gravitational waves at frequencies above 40 Hz. Much like the case of electromagnetism, there is a strong science case to observationally probe other parts of the gravitational wave spectrum. Significant advances on this front have been made in the mHz band by the LISA collaboration and the nHz range by the NanoGRAV collaboration. How might be probe other gravitational wave frequencies? In this talk, I will discuss the use of atom interferometers to probe gravitational waves in the 1 Hz band. I will also explore the potential use of asteroids as test masses to detect gravitational waves at micro Hz frequencies and the possible use of astrometry in the nHz - micro Hz regime.
Colloquia
Date:
27
October, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid Colloquium
Anomalous thermal relaxations: with and without a phase transition
What is the fastest way to heat a system? A naive approach that we commonly use in our kitchen is to put the system in the hottest oven available. Somewhat counter-intuitively, this naive approach is not always optimal: for some systems a pre-cooling stage can significantly accelerate the heating. Such non-monotonic optimal heating protocols are one type of anomalous thermal relaxations. In this talk I will discuss several types of anomalous thermal relaxations, give some intuition for their existence, explain how to find them in large, many body systems and present some recent results on anomalous relaxations through a second order phase transition.
Dipolar interactions are fundamentally different from the usual van der Waals forces in real gases. Besides its anisotropy the dipolar interaction is nonlocal and as such allows for self organized structure formation, like in many different fields of physics. Although the bosonic dipolar quantum liquid is very dilute, stable droplets and supersolids as well as honeycomb or labyrinth patterns can be formed due to the presence of quantum fluctuations beyond the mean field theory.
The Physics faculty invites all its members, family and friends to the upcoming concert ‘Music by the Pond' with collaboration of SRITP - Advanced SRitp and GiRYD School on Giant Interactions in Rydberg Systems, by "The Records" band to be held on Wednesday, 21.9.22 at 16:45. Beer from a boutique brewery will be sold. Feel free to bring with you a beach mat/chair, drinks, and snacks.
Workshops & Conferences
Date:
11
12
September, 2022
Monday
Hour: 08:00
School on Biological Physics of Cells (PhysCell2022)
In the present seminar, I will introduce how the flat bands in the magic angle twisted bilayer graphene (MATBG) can be understood from the zeroth Landau levels under the twisting generated pseudo magnetic field. These pseudo Landau level wave functions are almost the exact Eigen solutions of the real space Hamiltonian around the AA stacking center and can be further viewed as the analog of the “atomic core level” states in the band structure calculations for the ordinary crystals. In addition, we can use the pseudo zeroth Landau level (PZLL) and the “orthogonalised plane waves” (OPW) made from the PZLL as the two types of basis functions to efficiently reconstruct the entire Moire band structure. Using these PZLL and OPW basis functions, we can describe both the localised and itinerant components in the Moire bands of MATBG and map the MATBG to a “heavy fermion” like system, which can be used to study the orbital magnetism, topology and strongly correlation physics in MATBG.
The Physics faculty invites all its members, family and friends to the upcoming concert of the summer-time ‘Music by the Pond' with collaboration of SRITP - Hammers and Nails 3 workshop by "Shuffle" band to be held on Monday, 8.8.22 at 17:15
Beer from a boutique brewery will be sold.
Feel free to bring with you a beach mat/chair, drinks, and snacks
The second quantum revolution relies on our ability to control and measure individual quantum states in micro- and nanoscopic systems, such as atoms, ions, and quantum dots. The techniques resulting from this capability may lead to a considerable improvement in several sensing modalities, for example atomic clocks and the measurement of magnetic fields on the nanoscale.
As an example for a quantum sensor, and of course after introducing the underlying concepts of quantum sensing, I will present the nitrogen-vacancy defect, or color center, in diamond. First, I will explain how one can use it to measure magnetic and electric fields, temperature, strain and even pH levels. Then, I will try to show what the "quantum advantage" that is possible in this class of sensors and will give a few examples from research activities in our group. Finally, I will also discuss several industrial applications, some of which are already in use or in development around the world.
It's been exactly 10 years since the Higgs Boson Discovery (July 4th, 2012). The Higgs Boson discovery is the biggest achievement of the Large Hadron Collider (LHC) at CERN, and one of the milestones of experimental Particle Physics. We will describe the road to the Higgs Boson discovery, its importance, and the status of the measurement of its properties since its discovery.
Colloquia
Date:
05
July, 2022
Tuesday
Hour: 11:15-12:30
Special Physics colloquium
The Electron’s Spin and Chirality - A Miraculous Match
Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we established that chiral material can act as spin filters for photoelectrons transmission, in electron transfer, and in electron transport. The effect, termed Chiral Induced Spin Selectivity (CISS), has interesting implications for the production of new types of spintronics devices and on electron transfer in biological systems. The basic effect, and its applications and implications, will be presented.
Colloquia
Date:
30
June, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid Colloquium
The construction of the Vera Rubin Observatory and cosmological measurements of dark matter and dark energy with LSST
The Legacy Survey of Space and Time (LSST), the first project to be undertaken
at the new Vera Rubin Observatory, will be the most comprehensive optical astronomical
survey ever undertaken. Starting in 2024, Rubin Observatory will obtain panoramic images
covering the sky visible from its location in Chile every clear night for ten years.
The resulting hundreds of petabytes of imaging data, essentially a digital color movie
of the night sky, will include about 40 billion stars and galaxies, and will be used for investigations ranging from cataloging dangerous near-Earth asteroids to fundamental
physics such as characterization of dark matter and dark energy.
I will start my presentation with an overview of LSST science drivers and system design,
and continue with a construction status report for the Vera Rubin Observatory. I will
conclude with a brief discussion of a few Big Data challenges that need to be addressed
before LSST data can be used for precise cosmological measurements.
Recent detections of gravitational waves (‘ripples in spacetime’) have produced startling revelations about the nature of the high energy Universe. Since the first direct detection of gravitational waves in 2015 emitted by the collision and merger of two black holes located more than one billion light years away, we are beginning to answer fundamental and long standing questions about black holes, neutron stars, gravity, and even the origins of the heaviest elements found in nature.
Colloquia
Date:
16
June, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid colloquium
Statistical Mechanics of Mutilated Sheets and Shells
Understanding deformations of macroscopic thin plates and shells has a long and rich history, culminating with the Foeppl-von Karman equations in 1904, a precursor of general relativity characterized by a dimensionless coupling constant (the "Foeppl-von Karman number") that can easily reach vK = 10^7 in an ordinary sheet of writing paper. However, thermal fluctuations in thin elastic membranes fundamentally alter the long wavelength physics, as exemplified by experiments that twist and bend individual atomically-thin free-standing graphene sheets (with vK = 10^13!) With thermalized graphene sheets, it may be possible to study the quantum mechanics of two dimensional Dirac massless fermions in a fluctuating curved background whose dynamics resembles a simplified form of general relativity. We then move on to analyze the physics of sheets mutilated with puckers and stitches. Puckers and stitches lead to Ising-like phase transitions that strongly affect the physics of the fluctuating sheet. Thin shells with a background curvature that couples in-plane stretching modes with the out-of-plane undulations, exhibit a critical size for thermalized spherical shells, beyond which they must inevitably collapse.
Seminars
Date:
12
June, 2022
Sunday
Hour: 13:00
WIS-Q Seminar
Topological Superconductivity, Majorana fermions, and their Application to Quantum Computation
A topological superconductor is a unique state of matter. Its non-Abelian variant has zero- energy excitations (or particles) known as the Majorana zero modes. These modes have emerged as a critical component for topological quantum computation. Similar to a classical ferromagnet state, in which the interactions between the spins suppress single spin fluctuations, the topological superconductor self-corrects errors in the qubit operations carried by the Majorana zero modes. This talk will briefly discuss the Majoranas' unique non- abelian character and how we can use them to achieve fault-tolerance quantum processing. We will describe how the Majorana zero modes emerge in topological superconductors, the current experimental progress in finding this unique state of matter in nature, and the strategies to address the challenges in its realization.
Multiparton interactions in proton-proton collisions have long been a topic of great interest. A new look at them has begun to emerge from work being done to understand the dynamics of ‘small systems’, a topic that is taking center stage in the physics of relativistic heavy-ion interactions. Numerous studies conducted at the LHC and lower energies reveal that proton-proton collisions at high energy form a system in which final state interactions substantially impact experimentally observable quantities in the soft sector. However, until recently, no evidence was shown that final state interactions could also affect observables produced in the hard scattering processes. Studies performed by the LHC experiments present strong evidence that the final state interactions in proton-proton collisions have a drastic impact on the b-quark bound states production, whose yields may be reduced by more than a factor of two.
For nearly three decades, ultracold atomic gases have been used with great success to study fundamental many-body phenomena such as Bose-Einstein condensation and superfluidity. While traditionally they were produced in harmonic electromagnetic traps and thus had inhomogeneous densities, it is now also possible to create homogeneous samples in the uniform potential of an optical box trap. Box trapping simplifies the interpretation of experimental results, provides more direct connections with theory and, in some cases, allows qualitatively new, hitherto impossible experiments. I will give an overview of our recent experiments with box-trapped three- and two-dimensional Bose gases, focusing on a series of related experiments on non-equilibrium phenomena, including phase-transition dynamics, turbulence, and equilibration of closed quantum systems
Colloquia
Date:
19
May, 2022
Thursday
Hour: 11:15-12:30
Physics Hybrid Colloquium
X-ray polarimetry for detection of vacuum birefringence & The Helium hydride ion in strong laser fields
X-ray precision polarimetry and the detection of vacuum birefringence
Vacuum isn’t just empty space. Rather there is a continuous creation and annihilation of virtual pairs. A strong electric field can align them to a certain degree such that vacuum becomes birefringent – according to quantum electrodynamics. The effect has been predicted almost 90 years ago, but never been directly verified to date.
We have been developing X-ray polarimetry over the past 12 years in order to detect vacuum birefringence. The current status is an extinction ratio of 11 orders of magnitude using channel-cut crystals. This is a figure not nearly matched by any other polarimeter in any spectral region. Besides the physics of X-ray polarimetry, I will also discuss the remaining issues for the detection of vacuum birefringence.
The Helium hydride ion in strong laser fields
The Helium hydride ion is considered to be the first molecule that has formed after the big bang, a fact already pointing to the fundamental importance of this ion. Nevertheless, its behavior in intense, ultrashort laser fields has not been addressed until recently. This is in strong contrast to another fundamentally important molecule, the hydrogen molecular ion, on which many thousands of papers have been published.
I will discuss a series of experiments using different isotopologues of the Helium hydride ion at different wavelengths. The dissociation and ionization dynamics turns out to be vastly different from the hydrogen molecular ion. Moreover, it changes dramatically when moving from the near- to the mid-infrared spectral region. Although Helium hydride and the hydrogen molecule are isoelectronic, they can be seen as opposing extremes.
Seminars
Date:
12
May, 2022
Thursday
Hour: 12:30-14:30
WIS-Q Seminar
Photonic Route to Fault-tolerant Quantum Computing
I will describe the photonic approach to quantum computation, which is the only technology that has been originally designed to reach the massive scaling required for fault- tolerant universal computation (> 106 physical qubits). It combines topological error correction and measurement-based quantum computation, with the leading effort relying on massive-scale silicon photonics.
I will then describe how cavity-QED with single atoms allows deterministic photon-atom two qubit gates, which in turn can drastically simplify the road towards fault-tolerant photonic quantum computing and improve its scaling to even larger numbers of physical qubits.
The last decade has seen a tremendous improvement in theoretical understanding of galaxy clustering on cosmological scales, which culminated in recent CMB-independent measurement of cosmological parameters from spectroscopic galaxy surveys. In particular, these results are in agreement with the CMB estimates of the Hubble constant and they provide an important additional piece of the Hubble tension puzzle. In this talk I will review the main theoretical and practical developments which led to this progress. I will also highlight the main lessons we learned so far and discuss further improvements that have to be made in order to optimally extract information from the ongoing galaxy surveys such as DESI and Euclid. I will conclude by arguing that in the next couple of years the large-scale structure will become as powerful probe of cosmology as the CMB, and show the immense potential that the combination of the two has in answering many of the open questions in cosmology, including resolution of the Hubble tension.
We present a modification of quantum mechanics in which a specific class of state-dependent term is added to the Schroedinger Equation. We show that this term produces non-trivial effects which amount to the ‘wave function talking to itself’. We show that these effects are nevertheless causal (don’t violate relativity) while having profound experimental consequences. We also show that this modification has a simple embedding in local quantum field theory. While the physical effects are dramatic, they are also fickle, in that their strength depends on the cosmological history of the wave function of the universe. We will present proposals for laboratory (e.g., AMO), astrophysical, and cosmological tests that could be done to discover such an effect.
Colloquia
Date:
12
April, 2022
Tuesday
Hour: 11:15-12:30
Physics Hybrid Colloquium
Topological Quantum Computation with Majorana zero-energy modes
Roman Lutchyn | Microsoft Quantum
11:00 - Coffee, tea and more...(outside of the auditorium)
Abstract: Research in quantum computing has offered many new physical insights and a potential to exponentially increase the computational power that can be harnessed to solve important problems in science and technology. The largest fundamental barrier to building a scalable quantum computer is errors caused by decoherence. Topological quantum computing overcomes this barrier by exploiting topological materials which, by their nature, limit errors. In this colloquium, I will discuss how to engineer topological superconductors supporting Majorana zero-energy modes at the interface of a conventional superconductor and a semiconductor with spin-orbit interaction. I will present recent results by the Microsoft Quantum team consistent with the emergence of topological superconductivity in proximitized semiconductor nanowires. Finally, I will present a proposal for scalable quantum computing involving topological qubits which comprise of superconducting islands in a Coulomb blockade regime hosting aggregates of four or more Majorana zero modes.
It is fairly well known that Shor's algorithm for Factoring and Discrete Logarithm poses a challenge for cryptography in a quantum world. However, the implications of the viability of the quantum model on cryptography are much more profound, on a number of aspects. Naturally, it is harder to protect against quantum attackers than against classical ones, especially if the honest users remain classical. On the other hand, quantum computation and communication also present new tools that may assist in performing some cryptographic tasks. Further, the quantum model brings about new potential capabilities and cryptographic tasks that need to be explored, most basically the ability to prove that a potentially untrusted device indeed performs a quantum task.
In the talk I will explain how computer scientists, and in particular cryptographers, perceive the quantum computing model. I will discuss some of the fundamental questions that come up when the quantum model is incorporated into cryptography, such as the security of "lattice assumptions" against quantum attacks, the rewinding problem in cryptographic reductions, and the notion of semi-quantum cryptography which addresses questions in classical-quantum interaction.
No background in computer science or cryptography will be assumed.
Hybrid seminar
Location: Physics library (Benoziyo Physics building, second floor)
Zoom link: https://weizmann.zoom.us/j/99771276053?pwd=K3N6NEpPemh6aDZ2dEpJUU5HRXo4UT09
Phase separation is generally a thermodynamic process in which a mixture reaches its lowest free energy state by self-assembling into meso- (or macro-) scale regions that are concentrated or dilute in a given molecular component. Familiar examples include the immiscibility of water and oil, the demixing of metal atoms in alloys, and the mesoscale formation of emulsions such as milk or paint. The fundamental physics behind both the equilibrium and non-equilibrium aspects of phase separation are well understood and this talk will begin with a brief review of those. A rapidly growing body of experiments suggests that phase separation is responsible for the formation of membraneless domains (also known as biomolecular condensates, with length scales on the order of microns) in biological cells. These compartments allow the cell to organize itself in space and can promote or inhibit biochemical reactions, provide regions in which macromolecular assemblies can form, or control the spatial organization of DNA (assembled with proteins as chromatin) in the cell nucleus. I will review some recent examples based on experiments done at the Weizmann Institute on phase separation of proteins and of chromatin in the nucleus and show how physics theory has led to their understanding. In the latter case, a new paradigm is emerging in which the genetic material is not necessarily uniformly distributed within the nucleus but separated into domains which in some cases, have a complex, “marshland”, mesoscale structure. But while many of the equilibrium aspects can be at least semi-quantitatively understood by extensions of statistical physics, biological systems often do not have constant overall compositions as is the case in the examples of oil-water, alloys and emulsions; for example, over time, the cell produces and degrades many proteins. The recent understanding of such strongly non-equilibrium effects has informed the theoretical physics of phase separation and has allowed us to establish a framework in which biological noise can be included.
* Collaborations: Omar Arana-Adame, Gaurav Bajpai, Dan Deviri, Amit Kumar (Dept. Chemical and Biological Physics), group of Emmanuel Levy (Dept. Structural Biology) and group of Talila Volk (Dept. Molecular Genetics)
Seminars
Date:
13
February, 2022
Sunday
Hour: 13:00
WIS-Q Seminar
Trapped ions quantum computing – a tale of highly social qubits
In this talk I will review the basic methods and the current state-of-the-art in trapped ion quantum computing and compare the advantages and disadvantages of this to other QC technologies. I will further describe the progress towards building the WeizQC - a trapped ion quantum computer at the Weizmann Institute of Science. In the second part of the talk I will describe one unique feature of trapped-ion qubits: their all-to-all connectivity. I will describe methods that use this connectivity to engineer multi-qubit gates and operations. Multi-qubit gates have many advantages, both for near term noisy quantum computers, as well as for achieving fault-tolerance. As an example I will show that using multi-qubit gates, the threshold for fault-tolerant quantum computing can be enlarged and the ratio of logical to physical qubit error reduced.
Colloquia
Date:
20
January, 2022
Thursday
Hour: 11:15-12:30
Physics Virtual Colloquium
Experiments on superconducting processors at the dawn of NISQ era
In 2019, the Google Quantum team demonstrated that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical computer, the quantum supremacy. Going beyond this milestone, we now seek to utilize these Noisy Intermediate Scale Quantum (NISQ) processors to find algorithms that are of interest to the broader scientific community. However, achieving this goal is an outstanding challenge both theoretically, e.g. in finding suitable algorithms, as well as experimentally, e.g. extending coherence of the system. By presenting some of our recent works, we discuss the challenges and our progress. In particular, we present results on preparing the ground state of the Toric code Hamiltonian using an efficient quantum circuit [1]. Combining various techniques, we study transitions to the time crystalline phase [2], which is challenging due to limited programmability, finite coherence time, and finite size of current processors. Our results demonstrate the promise of studying condensed matter problems with NISQ processors.
[1] Satzinger et al., Science (2021)
[2] Mi et al., Nature (2021)
Seminars
Date:
17
January, 2022
Monday
Hour: 12:30
MicroBooNE's new results from the deep-learning-based 2-body CCQE search for an electron neutrino excess
Abstract:The MicroBooNE detector is a liquid argon time projection chamber (LArTPC) located on-axis in the Booster Neutrino Beam (BNB) at Fermi National Laboratory. One of the primary goals of the experiment is to investigate the excess over background expectations of electromagnetic-like events observed by MiniBooNE at low energies. In this talk, I will present the latest results from MicroBooNe's four analyses, with a focus on the 2-body CCQE search, which utilizes deep learning and traditional techniques.
Seminars
Date:
09
January, 2022
Sunday
Hour: 13:00
WIS-Q Seminar
Computing the Quantum: Classical and Quantum Simulations of Many-Body Systems
Many problems of interest, ranging from condensed matter physics and quantum chemistry to quantum information, require finding the ground state of a system of many interacting degrees of freedom (e.g., qubits or quantum spins). The main challenge stems from the exponential scaling of the Hilbert space dimension with the number of qubits. I will first discuss various strategies to tackle this problem using classical computers, such as tensor network states and Monte Carlo sampling, and their limitations. Quantum computers are ideally suited for this task; I will present a proposal to simulate quantum systems on noisy intermediate-scale quantum (NISQ) devices made of imperfect qubits, where the noise level translates into a finite energy density (i.e., finite temperature).
