PreprintCC BY 4.0arXiv
Attainable and unattainable quantum precision limits in ultrastrong light--matter coupling
Abstract
In this paper, we study the gauge dependence of quantum precision in ultrastrongly coupled light--matter systems. The unitary between gauges carries the coupling g, so each truncation defines a different family. The quantum Fisher information traces an exact parabola across frames. Harmonic matter minimizes it at a universal θ∗=Ω/(Ω+ω), set by the matter and cavity frequencies. Only the minimal-coupling bound is attainable. Frames differ by a factor $9.6$ with opposite trends. Diverging virtual-excitation gain at the Dicke point is a gauge artifact and saturates.
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BibTeX
@misc{lu2026attainable,
title = {{Attainable and unattainable quantum precision limits in ultrastrong light--matter coupling}},
author = {Wangjun Lu and Qing Yu},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.12471},
eprint = {2611.12471},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.12471},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Attainable and unattainable quantum precision limits in ultrastrong light--matter coupling
AU - Wangjun Lu
AU - Qing Yu
PY - 2026
DA - 2026/11/09
PB - arXiv
DO - 10.48550/arxiv.2611.12471
UR - https://arxiv.org/abs/2611.12471
AB - In this paper, we study the gauge dependence of quantum precision in ultrastrongly coupled light--matter systems. The unitary between gauges carries the coupling g, so each truncation defines a different family. The quantum Fisher information traces an exact parabola across frames. Harmonic matter minimizes it at a universal θ_∗=Ω/(Ω+ω), set by the matter and cavity frequencies. Only the minimal-coupling bound is attainable. Frames differ by a factor $9.6$ with opposite trends. Diverging virtual-excitation gain at the Dicke point is a gauge artifact and saturates.
ER -