1. from dual-unitary to quantum bernoulli circuits: entangling power’s role in constructing a quantum ergodic hierarchy

Arul Lakshminarayan

Indian Institute of Technology, India

4 February 2021 Thu 4 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Deterministic classical dynamical systems have an ergodic hierarchy, from ergodic through mixing, to Bernoulli systems that are "as random as a coin-toss". Dual-unitary circuits have been recently introduced as solvable models of many-body nonintegrable quantum chaotic systems having a hierarchy of ergodic properties. We extend this to include the apex of a putative quantum ergodic hierarchy which is Bernoulli, in the sense that correlations of single and two-particle observables vanish at space-time separated points. We derive a condition based on the entangling power ep(U) of the basic two-particle unitary building block, U, of the circuit, that guarantees mixing, and when maximized, corresponds to Bernoulli circuits. Additionally we show, both analytically and numerically, how local-averaging over single-particle unitaries leads to an identification of the average mixing rate as being determined solely by the entangling power ep(U). The same considerations extend to disordered dual-unitary circuits as well. Finally we provide several, both analytical and numerical, ways to construct dual-unitary operators covering the entire possible range of entangling power. We construct a coupled quantum cat map which is dual-unitary for all local dimensions and a 2-unitary or perfect tensor for odd local dimensions, and can be used to build Bernoulli circuits. These constructions and results pave the way for a systematic extension of quantities studied in the dual-unitary circuits as well as provide natural generalizations to the non-dual cases.

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