March 2023 Meeting

Speakers & Abstracts

Brian Swingle

Title: Tensor Networks and Low Energy Dynamics

Abstract:

Sam Garratt

Title: Measurements conspire nonlocally to restructure critical quantum states

Abstract: I will discuss the effects of local measurements on critical quantum ground states. In critical states there are algebraic correlations between local observables and, as a consequence, local measurements can have highly nonlocal effects. This raises the possibility for a new class of collective phenomenon arising from the conspiracy of commuting measurements alone. In certain scenarios the post-measurement state has qualitatively different correlations to the original ground state, while in others the original correlations are robust, and I will discuss a sharp transition between these two regimes. Because there is no dynamics in the problem this behavior is robust to local decoherence, although a post-selection problem poses a barrier to their direct observation. I will show that resource-efficient probes are instead to be found in cross-correlations between experimental measurement results and simulations on classical computers.

References

S. J. Garratt, Z. Weinstein, E. Altman 2207.09476 (to appear in PRX)

Z. Weinstein, R. Sajith, E. Altman, S. J. Garratt 2301.08268

Matteo Ippoliti

Title: Phases of quantum information on a noisy quantum processor

Abstract: I will present new work in collaboration with Google Quantum AI [ https://arxiv.org/abs/2303.04792 ] in which measurement-induced phases of quantum information are realized on up to 70 superconducting qubits. Detection of these phases is nontrivial, and requires the formulation of hybrid quantum-classical order parameters that correlate quantum readout data with classical simulation. One such diagnostic has a natural interpretation in terms of emergent quantum teleportation.

Jinzhao Wang

Title: On some information-theoretic questions in double-scaled SYK and JT gravity

Abstract: I will formulate some information-theoretic questions in the double-scaled SYK model, which can help probe some features of the bulk dual. I will test these ideas in both the JT gravity limit and the large q SYK regime.

Alex May

Title: Constraints on physical computers in holographic spacetimes

Abstract: Within the setting of the AdS/CFT correspondence, we ask about the power of computers in the presence of gravity. We use a boundary argument to show that there are computations on $n$ qubits which cannot be implemented inside of black holes with entropy less than $\Theta(2^n)$. To establish our claim, we argue computations happening inside the black hole must be implementable in a programmable quantum processor, so long as the inputs and description of the unitary to be run are not too large. We then prove a bound on quantum processors which shows many unitaries cannot be implemented inside the black hole, and further show some of these have short descriptions and act on small systems. These unitaries are computationally forbidden from happening inside the black hole.