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arXiv · 2303.15507

Mixed-state long-range order and criticality from measurement and feedback

Tsung-Cheng Lu·Zhehao Zhang·Sagar Vijay·Timothy H. Hsieh
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Abstract

We propose a general framework for using local measurements, local unitaries, and non-local classical communication to construct quantum channels which can efficiently prepare mixed states with long-range quantum order or quantum criticality. As an illustration, symmetry-protected topological (SPT) phases can be universally converted into mixed-states with long-range entanglement, which can undergo phase transitions with quantum critical correlations of local operators and a logarithmic scaling of the entanglement negativity, despite coexisting with volume-law entropy. Within the same framework, we present two applications using fermion occupation number measurement to convert (i) spinful free fermions in one dimension into a quantum-critical mixed state with enhanced algebraic correlations between spins and (ii) Chern insulators into a mixed state with critical quantum correlations in the bulk. The latter is an example where mixed-state quantum criticality can emerge from a gapped state of matter in constant depth using local quantum operations and non-local classical communication.

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Tsung-Cheng Lu, Zhehao Zhang, Sagar Vijay, Timothy H. Hsieh. 2023-03-27. Mixed-state long-range order and criticality from measurement and feedback. https://doi.org/10.1103/prxquantum.4.030318

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