Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session K24: Dynamical Entanglement Transitions in Monitored Random Quantum CircuitsInvited

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Sponsoring Units: DCMP Chair: Pashupati Dhakal, Jefferson Lab/Jefferson Science Associat Room: Room 237 
Tuesday, March 7, 2023 3:00PM  3:36PM 
K24.00001: Quantum Dynamics in Noisy and Monitored Random Circuits Invited Speaker: Michael J Gullans The sustained storage, transmission, or processing of quantum information will likely be a nonequilibrium process that requires monitoring the system and applying some form of feedback to produce faulttolerance. In this talk, I will discuss a class of models based on random quantum circuits with intermediate measurements that display a similar phenomenology to standard models for faulttolerance, including the existence of a threshold, but with several helpful simplifications. I will discuss recent progress on understanding this novel class quantum phases and quantum critical phenomena. The emphasis will be on describing efficient protocols we have developed that allow experimental access in noisyintermediate scale quantum processors. 
Tuesday, March 7, 2023 3:36PM  4:12PM 
K24.00002: Cross Entropy Benchmark for MeasurementInduced Phase Transitions Invited Speaker: Matthew A Fisher Open quantum dynamics can host a rich phenomenology, including a family of measurementinduced phase transitions (MIPT) in the scaling of entanglement along quantum trajectories in monitored systems. While the MIPT occurs generically in a number of different models, its verification can be challenging even on an errorcorrected quantum computer, due to the socalled ``postselection problem". I will describe the prospects of employing the linear crossentropy to experimentally access measurementinduced phase transitions (MIPT) without requiring any postselection of quantum trajectories. By running two random circuits that are identical in the bulk but with different initial states  one on a quantum and the other on a classical computer  the linear cross entropy between the bulk measurement outcome distributions in the two circuits can be used to distinguish the volume law from area law phases. Besides the volumelaw to area law MIPT, the linear crossentropy can be employed to access other dynamical phase transitions in monitored systems, as I will describe. 
Tuesday, March 7, 2023 4:12PM  4:48PM 
K24.00003: Topological transitions in weakly monitored free fermions Invited Speaker: Dganit Meidan We study a free fermion model where two sets of noncommuting nonprojective measurements stabilize arealaw entanglement scaling phases of distinct topological order. We show the presence of a topological phase transition that is of a different universality class than that observed in stroboscopic projective circuits. In the presence of unitary dynamics, the two topologically distinct phases are separated by a region with subvolume scaling of the entanglement entropy. We find that this entanglement transition is well identified by a emph{combination} of the bipartite entanglement entropy and the topological entanglement entropy. 
Tuesday, March 7, 2023 4:48PM  5:24PM 
K24.00004: An entanglement transition on a quantum tree and its relation to the measurement transition in alltoall circuits Invited Speaker: Jonathan Ruhman The measurement phase transition is a dynamical transition resulting from the competition between entangling gates and nonunitary operations. Its universal properties are known exactly in a type of classical limit obtained by considering the Hartley function or by taking the local Hilbert space dimension to infinity. It can also be understood using numerics on large systems for specific fine tuned models, such as Clifford or automaton circuits. In all these cases the universality of the transition is some version of percolation (or close to it). However, we do not have such a comprehensive understanding of its nature for generic quantum evolution, beyond small system numerics. I will describe our work on alltoall circuits, where we argue that the transition is controlled by an entanglement transition on a tree tensor network. In this case rigorous results can be obtained for generic entangling gates. We show that this transition occurs at a finite distance from the classical percolation transition and also has a different universality class. 
Tuesday, March 7, 2023 5:24PM  6:00PM 
K24.00005: Measurement and feedback driven entanglement transition in the probabilistic control of chaos Invited Speaker: Thomas Iadecola We uncover a dynamical entanglement transition in a monitored quantum system that is heralded 
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