Quantum Criticality Under Decoherence or Weak Measurement

By Jong Yeon Lee, Chao-Ming Jian, Cenke Xu. PRX Quantum, 2023

199 citations recorded by the source corpus.

Decoherence inevitably happens when a quantum state is exposed to its environment, which can affect quantum critical points (QCP) in a nontrivial way. As was pointed out in recent literature on $(1+1)d$ conformal field theory (CFT), the effect of weak measurement can be mathematically mapped to the problem of boundary CFT. In this work, we focus on the $(2+1)d$ QCPs, whose boundary and defect effects have attracted enormous theoretical and numerical interests very recently. We focus on decoherence caused by weak measurements with and without post-selecting the measurement outcomes. Our main results are: (1) for an O(N) Wilson-Fisher QCP under weak measurement with post-selection, an observer would in general observe two different types of boundary/defect criticality with very different behaviors from the well-known Wilson-Fisher fixed points; in particular, it is possible to observe the recently proposed exotic"extraordinary-log"correlation. (2) An extra quantum phase transition can be driven by decoherence, if we consider quantities nonlinear with the decohered density matrix, such as the Renyi entropy. We demonstrate the connection between this transition to the information-theoretic transition driven by an error in the toric code model. (3) When there is no post-selection, though correlation functions between local operators remain the same as the undecohered pure state, nonlocal operators such as the"disorder operator"would have qualitatively distinct behaviors; and we also show that the decoherence can lead to confinement.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics

View Paper: https://www.semanticscholar.org/paper/4b10984300a2d62cd07d3e662287c52ea8604962

How researchers see this paper

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In Atomic and Molecular Physics, and Optics

1. Yimu Bao
2. Ruihua Fan
3. Ashvin Vishwanath
4. E. Altman
5. A. Nahum
6. Matthew Fisher
7. V. Khemani
8. T. Senthil

In Condensed Matter Physics

1. Ashvin Vishwanath
2. E. Altman
3. S. Sachdev

Citations in the corpus

• Diagnostics of Mixed-State Topological Order and Breakdown of Quantum Memory (2023, background): “It is unclear whether the three diagnostics still exhibit transition simultaneously, which may be an interesting question for future study.”