Strong-to-Weak Spontaneous Symmetry Breaking Transitions on a Quantum Processor
Abstract
Mixed quantum states can exhibit unconventional forms of symmetry breaking without pure-state counterparts. A prominent example is strong-to-weak spontaneous symmetry breaking (SW-SSB), which cannot be diagnosed by observables linear in the density matrix. Here, we experimentally resolve finite-size critical signatures of SW-SSB transitions on a superconducting quantum processor. We develop a measurement protocol that combines quantum measurements with classical processing based on the known dephasing channel to reconstruct nonlinear mixed-state correlators. Using only two measurement settings, the protocol reconstructs fidelity, Rényi-2, and linear correlators, as well as string observables. Applying this approach to matrix-product states subjected to power-law-correlated dephasing, we observe finite-size crossings and scaling collapses in nonlinear correlators, accompanied by decaying linear correlations. We further map the estimated SW-SSB transition points across initial-state and channel parameters. Measurements of linear and Rényi-2 string observables further reveal signatures of mixed-state symmetry-protected topological (SPT) phases, with a nonlinear string-order crossover aligned with an independently estimated SW-SSB transition point. Our results establish a quantum-classical approach to probing SW-SSB critical behavior and mixed-state SPT order.
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BibTeX
@misc{wei2026strongtoweak,
title = {{Strong-to-Weak Spontaneous Symmetry Breaking Transitions on a Quantum Processor}},
author = {Zhi-Yuan Wei and Christopher Fechisin and Yu-Xin Wang and Jeet Shah and Tsung-Cheng Lu and Cheng-Ju Lin and Alexey V. Gorshkov},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.26229},
eprint = {2610.26229},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.26229},
}
RIS
TY - UNPB
TI - Strong-to-Weak Spontaneous Symmetry Breaking Transitions on a Quantum Processor
AU - Zhi-Yuan Wei
AU - Christopher Fechisin
AU - Yu-Xin Wang
AU - Jeet Shah
AU - Tsung-Cheng Lu
AU - Cheng-Ju Lin
AU - Alexey V. Gorshkov
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.26229
UR - https://arxiv.org/abs/2610.26229
AB - Mixed quantum states can exhibit unconventional forms of symmetry breaking without pure-state counterparts. A prominent example is strong-to-weak spontaneous symmetry breaking (SW-SSB), which cannot be diagnosed by observables linear in the density matrix. Here, we experimentally resolve finite-size critical signatures of SW-SSB transitions on a superconducting quantum processor. We develop a measurement protocol that combines quantum measurements with classical processing based on the known dephasing channel to reconstruct nonlinear mixed-state correlators. Using only two measurement settings, the protocol reconstructs fidelity, Rényi-2, and linear correlators, as well as string observables. Applying this approach to matrix-product states subjected to power-law-correlated dephasing, we observe finite-size crossings and scaling collapses in nonlinear correlators, accompanied by decaying linear correlations. We further map the estimated SW-SSB transition points across initial-state and channel parameters. Measurements of linear and Rényi-2 string observables further reveal signatures of mixed-state symmetry-protected topological (SPT) phases, with a nonlinear string-order crossover aligned with an independently estimated SW-SSB transition point. Our results establish a quantum-classical approach to probing SW-SSB critical behavior and mixed-state SPT order.
ER -