Charge Scrambling in Strong-to-Weak Spontaneous Symmetry Breaking

TL;DR

This paper investigates how strong-to-weak spontaneous symmetry breaking (SWSSB) affects charge fluctuations and introduces new correlators to distinguish different symmetry-breaking and charge fluctuation regimes.

Contribution

It establishes a static fluctuation footprint of charge scrambling, introduces a twist overlap correlator, and clarifies the relationship between SWSSB, charge indefiniteness, and coherent fluctuations.

Findings

Long-range Rènyi-1 correlator implies extensive charge variance under SWSSB.

Dephased superfluids can retain SWSSB with subextensive charge variance.

The twist overlap correlator decomposes charge fluctuations into symmetry channels.

Abstract

Strong-to-weak spontaneous symmetry breaking (SWSSB) is diagnosed by nonlinear correlators, but its direct static implication for conserved charge fluctuations is not automatic. We show that, for continuous symmetries, long-range R\'enyi-1 correlator, together with a sufficiently rapid approach to its nonzero asymptotic value, forces subsystem charge indefiniteness: the block-charge variance has an extensive lower bound; equivalently, the truncated symmetry expectation has extensive curvature. This gives a precise static fluctuation footprint of charge scrambling. We construct examples to show that the implication is conditional and non-reversible: dephased superfluids retain R\'enyi-1 SWSSB with subextensive charge variance when the R\'enyi-1 tail is too slow, while sparse fixed-charge projectors have extensive charge variance but no local charge-transfer R\'enyi-1 order or long-range conditional mutual information. Finally, we introduce a \emph{twist overlap} correlator, which serves as an analogue of charge variance applicable to both discrete and continuous symmetries. This naturally decomposes local block-charge fluctuations into strong- and weak-symmetry channels. We found that the weak-symmetry channel isolates coherent charge fluctuations and is directly related to the Wigner--Yanase skew information. Taken together, these results give a unified understanding for distinguishing nonlinear SWSSB order, local charge indefiniteness, and coherent charge fluctuations.