Violation and revival of Kramers' degeneracy in open quantum systems

Article Materials Science, Multidisciplinary

Kramers' degeneracy for open systems in thermal equilibrium

Simon Lieu et al.

Summary: This study shows that the generator of dynamics for Markovian open fermionic systems can exhibit a degeneracy, which is protected by both time-reversal symmetry and the microreversibility property of systems at thermal equilibrium.

PHYSICAL REVIEW B (2022)

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Review Physics, Multidisciplinary

Exceptional topology of non-Hermitian systems

Emil J. Bergholtz et al.

Summary: This review discusses the current understanding of the role of topology in non-Hermitian systems and its physical consequences in dissipative settings, focusing on the concept of exceptional degeneracies and its distinct phenomena, as well as the new notions of gapped phases in single-band systems. The unique sensitivity of non-Hermitian matrices to boundary conditions is highlighted, leading to anomalous relationships between bulk and boundary physics. Additionally, applications of non-Hermitian topology in classical and quantum systems are reviewed, showing its relevance beyond the field of topological phases.

REVIEWS OF MODERN PHYSICS (2021)

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Article Physics, Particles & Fields

An obstacle to sub-AdS holography for SYK-like models

Pengfei Zhang et al.

Summary: In this study, stringy effects in a potential gravity-dual picture for SYK-like models are related to the branching time, which is a kinetic coefficient defined by the retarded kernel. A bound on the branching time is proposed when assuming the leading diagrams are ladders with thin rungs, suggesting that such models are unlikely candidates for sub-AdS holography. Additionally, in the weak coupling limit, a relationship between the branching time, Lyapunov exponent, and quasiparticle lifetime is derived using two different approximations.

JOURNAL OF HIGH ENERGY PHYSICS (2021)

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Review Physics, Multidisciplinary

Programmable quantum simulations of spin systems with trapped ions

C. Monroe et al.

Summary: Laser-cooled and trapped atomic ions provide an ideal platform for simulating interacting quantum spin models. By using optical fields to modulate the ions' Coulomb interaction, long-range and tunable spin-spin interactions can be produced. This quantum simulator allows for the study of complex equilibrium states and dynamical processes in many-body interacting quantum systems.

REVIEWS OF MODERN PHYSICS (2021)

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Article Physics, Multidisciplinary

Symmetry-Protected Topological Edge Modes and Emergent Partial Time-Reversal Symmetry Breaking in Open Quantum Many-Body Systems

Zijian Wang et al.

Summary: This article investigates the impact of a quantum bath on symmetry-protected topological edge modes, emphasizing the special role of time-reversal symmetry in open quantum systems. It is found that emergent partial time-reversal symmetry breaking can lead to the diffusion of topological modes from the system edge into the bath, rendering them ineffective for quantum computation.

PHYSICAL REVIEW LETTERS (2021)

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Article Physics, Multidisciplinary

Stability of Time-Reversal Symmetry Protected Topological Phases

Tian-Shu Deng et al.

Summary: This study investigates the stability of Kramers degeneracy and nontrivial topological states under time-reversal symmetry against coupling to the environment. The results show that dissipation can lead to splitting of spectral functions for degenerate states and induce backscattering between counterpropagating edge states, causing the absence of accurate quantization of conductance in the case of the quantum spin Hall effect. The findings have implications for interacting topological phases protected by time-reversal symmetry.

PHYSICAL REVIEW LETTERS (2021)

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Article Materials Science, Multidisciplinary

Elastic backscattering of quantum spin Hall edge modes from Coulomb interactions with nonmagnetic impurities

Max McGinley et al.

Summary: In this study, we demonstrate that electrostatic interactions between helical electrons at the edge of a quantum spin Hall insulator and a dynamical impurity can induce quasielastic backscattering, extending the range of known backscattering mechanisms. By modeling the impurity as a two-level system, transitions between counterpropagating Kramers-degenerate electronic states can occur without breaking time-reversal symmetry, with weak temperature dependence on the associated electrical resistance down to a nonuniversal temperature scale.

PHYSICAL REVIEW B (2021)

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Article Physics, Multidisciplinary

Disconnecting a traversable wormhole: Universal quench dynamics in random spin models

Tian-Gang Zhou et al.

Summary: Understanding strongly interacting quantum matter and quantum gravity are important open issues in theoretical physics. The holographic duality between quantum field theory and gravity theory helps connect these two topics. By utilizing gravity physics, this paper explains the quench dynamics observed in various quantum systems and finds universal features across different parameter regimes.

PHYSICAL REVIEW RESEARCH (2021)

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Article Physics, Particles & Fields