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Violation and Revival of Kramers' Degeneracy in Open Quantum Systems

Zhang, Pengfei and Chen, Yu (2021) Violation and Revival of Kramers' Degeneracy in Open Quantum Systems. . (Unpublished)

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Kramers' theorem ensures double degeneracy in the energy spectrum of a time-reversal symmetric fermionic system with half-integer total spin. Here we are now trying to go beyond the closed system and discuss Kramers' degeneracy in open systems out of equilibrium. In this letter, we prove that the Kramers' degeneracy in interacting fermionic systems is equivalent to the degeneracy in the spectra of different spins together with the vanishing of the inter-spin spectrum. We find the violation of Kramers' degeneracy in time-reversal symmetric open quantum systems is locked with whether the system reaches thermal equilibrium. After a sudden coupling to an environment in a time-reversal symmetry preserving way, the Kramers doublet experiences an energy splitting at a short time and then a recovery process. We verified the violation and revival of Kramers' degeneracy in a concrete model of interacting fermions and we find Kramers' degeneracy is restored after the local thermalization time. By contrast, for time-reversal symmetry ₸ with ₸² = 1, we find although there is a violation and revival of spectral degeneracy for different spins, the inter-spin spectral function is always nonzero. We also prove that the degeneracy in spectral function protected by unitary symmetry can be maintained always.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Zhang, Pengfei0000-0002-7408-0918
Chen, Yu0000-0002-0065-7622
Additional Information:Attribution 4.0 International (CC BY 4.0) P.Z. acknowledges support from the Walter Burke Institute for Theoretical Physics at Caltech. Y. C is supported by Beijing Natural Science Foundation (Z180013), and NSFC under Grant No. 11734010.
Group:Walter Burke Institute for Theoretical Physics, Institute for Quantum Information and Matter
Funding AgencyGrant Number
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Beijing Natural Science FoundationZ180013
National Natural Science Foundation of China11734010
Record Number:CaltechAUTHORS:20211018-185259557
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111529
Deposited By: George Porter
Deposited On:19 Oct 2021 15:04
Last Modified:19 Oct 2021 15:04

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