Shane Kelly: Coherence and Scrambling in Quantum Circuits Coupled to a Monitored Environment

Date of publication: 25. 4. 2023
Mathematical physics seminar
14:00 - 16:00
Kuščerjev seminar, Jadranska 19, 4. nadstropje

I will present our recent work on information transitions induced by coupling to an environmental. The first transition I will discuss occurs in a monitored random circuit where previously it was shown that a competition between unitaries and measurements can generate an entanglement transition. Instead here, we will show that an entanglement transition can instead be tuned by a competition between coherence generating and coherence destroying circuit elements. The second transition I will present occurs in a circuit that exchanges qubits with an environment as at a rate p. No measurements are preformed, but a transition in scrambling occurs tuned by the rate of coupling to the environment, p. Using the out-of-time-order correlator (OTOC) to characterize scrambling, we find a nonequilibrium phase transition in the directed percolation universality class at a critical swap rate, p_c: for pp_c, the OTOC fails to percolate within the system and vanishes uniformly after a finite time, indicating that all local operators are rapidly swapped into the environment. I will also present the consequences of both transitions for the encoding of quantum information. In the first case, we show how coherence is a requirement for quantum communication, provide coherence bounds for stabilizer error correction codes, and argue for a heuristic useful for classical simulations of open system dynamics with the potential of an exponential speed up. In the case of the scrambling transition, we present an efficient decoder whose fidelity undergoes transition that provides an experimentally viable way to observe a quantum information transition, circumventing the post selection problem known for measurement induced transitions.

Note: unusual time Tuesday at 2pm