Integrated Calendar

The high level of control achievable over quantized degrees of freedom have turned super-conducting circuits into one of the prime physical architectures for quantum computing and simulation. While conventional approaches mostly rely on unitary time evolution more recently open-system dynamics are considered for quantum information processing and simulations as well. In this talk, I will first give an introduction to superconducting quantum circuits. Then I will discuss a set of experiments in which we simulated the physics of interacting spins using a digital approach [1]. In a second set of experiments [2] we made use of an open cavity quantum electrodynamics (QED) system with tunable interactions to simulate the ground state of an interacting Bose gas confined in one dimension [3,4]. These experiments rely on our ability to efficiently measure higher order photon correlations of propagating microwave fields. To facilitate these measurements we developed a quantum limited amplifier achieving phase-preserving amplification at large bandwidth and high dynamic range [5]. Our results demonstrate an alternative path towards simulating complex quantum many-body physics based on the controlled generation and detection of nonclassical radiation in open quantum systems.


[1] Y. Salathe et al., Phys. Rev. X 5, 021027 (2015).

[2] C. Eichler et al., Phys. Rev. X 5, 041044 (2015).

[3] S. Barrett et al., Phys. Rev. Lett. 110, 090501 (2013).

[4] F. Verstraete and J. I. Cirac, Phys. Rev. Lett. 104, 190405 (2010).
[5] C. Eichler et al., Phys. Rev. Lett. 113, 110502 (2014).

Evidence has gradually accumulated that in AdS/CFT, any spatial subregion of the CFT has complete quantum information about some subregion of the bulk spacetime. Exactly which bulk subregion this is has been a matter of some debate, which has focused on the "causal wedge" and the "entanglement wedge" as the primary candidates. In this talk I will present a few theorems which together essentially resolve this debate in favor of the entanglement wedge. The argument combines recent work on quantum corrections to the Ryu-Takayanagi formula with the idea that the correspondence can be interpreted as a quantum error-correcting code.

: The Wheeler DeWitt equation is the statement that theories of gravity are topological in the bulk and only have boundary DOF. This fits with the Covariant entropy conjecture, which associates an areas worth of DOF to the boundary of a causal diamond. For nested diamonds it implies that the algebra of operators on the smaller one be a proper subalgebra of that on the larger one. Jacobson showed, conversely, that the area law implies Einstein's equations (except for the c.c., which Banks and Fischler argued was an asymptotic boundary condition). In Minkowski space, the maximal causal diamond is Penrose's conformal boundary. Traditionally we deal with this by introducing an S matrix, but this only works in perturbation theory because of the inevitable existence of states with arbitrary numbers of arbitrarily soft gravitons (even when there are no IR divergences). Instead we introduce an algebra of densities describing the flow of quantum numbers out to null infinity. The simplest of these are the commuting BMS local translations, which one can diagonalize. The joint spectrum of the past and future BMS generators defines a null cone, and all other currents may be thought of as generalized functions on this cone. The algebra must include helicity raising operators and the simplest way to introduce them (perhaps the only consistent way) is to write a generalization of the Awada Gibbons Shaw supersymmetric BMS algebra. One must define Sterman Weinberg jet representations of this algebra, which reveal that particle energy is related to constraints on the density degrees of freedom. Retreating from infinity to a finite causal diamond, the current algebra is cutoff by cutting off the spectrum of the Dirac operator on the holographic screen - a UV/IR correspondence reminiscent of that in AdS/CFT.