@article { WOS:000721731100001,
title = {Emergent Replica Conformal Symmetry in Non-Hermitian SYK2 Chains},
journal = {Quantum},
volume = {5},
year = {2021},
month = {NOV 16},
publisher = {VEREIN FORDERUNG OPEN ACCESS PUBLIZIERENS QUANTENWISSENSCHAF},
type = {Article},
abstract = {Recently, the steady states of non-unitary free fermion dynamics are found to exhibit novel critical phases with power-law squared correlations and a logarithmic subsystem entanglement. In this work, we theoretically understand the underlying physics by constructing solvable static/Brownian quadratic Sachdev-YeKitaev chains with non-Hermitian dynamics. We find the action of the replicated system generally shows (one or infinite copies of) O(2) x O(2) symmetries, which is broken to O(2) by the saddle-point solution. This leads to an emergent conformal field theory of the Goldstone modes. We derive the effective action and obtain the universal critical behaviors of squared correlators. Furthermore, the entanglement entropy of a subsystem A with length L-A corresponds to the energy of the half-vortex pair S similar to rho(s) log L-A, where rho(s) is the total stiffness of the Goldstone modes. We also discuss special limits with more than one branch of Goldstone modes and comment on interaction effects.},
issn = {2521-327X},
author = {Zhang, Pengfei and Jian, Shao-Kai and Liu, Chunxiao and Chen, Xiao}
}
@article { WOS:000704691400003,
title = {Measurement-Induced Phase Transition in the Monitored Sachdev-Ye-Kitaev Model},
journal = {Phys. Rev. Lett.},
volume = {127},
number = {14},
year = {2021},
month = {SEP 27},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We construct Brownian Sachdev-Ye-Kitaev (SYK) chains subjected to continuous monitoring and explore possible entanglement phase transitions therein. We analytically derive the effective action in the large-N limit and show that an entanglement transition is caused by the symmetry breaking in the enlarged replica space. In the noninteracting case with SYK2 chains, the model features a continuous O(2) symmetry between two replicas and a transition corresponding to spontaneous breaking of that symmetry upon varying the measurement rate. In the symmetry broken phase at low measurement rate, the emergent replica criticality associated with the Goldstone mode leads to a log-scaling entanglement entropy that can be attributed to the free energy of vortices. In the symmetric phase at higher measurement rate, the entanglement entropy obeys area-law scaling. In the interacting case, the continuous O(2) symmetry is explicitly lowered to a discrete C-4 symmetry, giving rise to volume-law entanglement entropy in the symmetry-broken phase due to the enhanced linear free energy cost of domain walls compared to vortices. The interacting transition is described by C-4 symmetry breaking. We also verify the large-N critical exponents by numerically solving the Schwinger-Dyson equation.},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.127.140601},
author = {Jian, Shao-Kai and Liu, Chunxiao and Chen, Xiao and Swingle, Brian and Zhang, Pengfei}
}