Joint ICTP/SISSA Condensed Matter Seminar, 27 April at 11:00am, Shane Kelly

[CMSP Seminars Secretariat]

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  Joint ICTP/SISSA Condensed Matter Seminar
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** * * Thursday**, 27 April 2023, 11:00**am ***(CET)** * **
In person: *Luigi Stasi Seminar Room **(Leonardo Building, second floor)***
**
/Zoom: 
https://zoom.us/meeting/register/tJwscOGrrjsoHtS5ewzYxnhhktlFf55wYHxP/<https://zoom.us/meeting/register/tJIsfuuhqjsrE9EZY2loNxNobg8Lf39NUVHJ>

Speaker: *Shane Kelly *(Johannes Gutenberg-Universität)

Title: *Coherence and Scrambling in Quantum Circuits Coupled to a 
Monitored Environment

*
Abstract:
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. Here, we will show that an entanglement 
transition can 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. 
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 p<p_c, the 
ensemble-averaged OTOC exhibits ballistic growth with a tunable light 
cone velocity, while for p>p_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 a transition that provides an 
experimentally viable way to observe a quantum information transition, 
circumventing the post selection problem known for measurement induced 
transitions.

https://arxiv.org/abs/2210.11547
https://arxiv.org/abs/2210.14242