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arXiv · 2606.31011

Qubit Readout via State-Dependent Radiative Linewidths

Yiming Yu·Xinyu Zhao·Jia-Wen Yu·Ke-Xiong Yan·Wei Qin·Ye-Hong Chen·Yan Xia·Franco Nori
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Abstract

Fast qubit readout conventionally encodes state information in a dispersive frequency shift. Here we formulate a linewidth-encoded quantum non-demolition measurement channel in which the qubit state enters the external radiative amplitude, equivalently a state-dependent Lindblad jump operator. Starting from an empty cavity, we show analytically that this dissipative channel imprints state information on the output field at $O(t)$, whereas standard dispersive readout starts at $O(t^2)$ because it requires intracavity buildup and conditional phase accumulation. This short-time scaling produces faster matched-filter signal-to-noise ratio accumulation and persists in finite-resource comparisons, including photon-number limits, external-linewidth budgets, cavity depletion, and pulse-optimized dispersive baselines. We further outline an auxiliary-mode route that converts a qubit-state-dependent auxiliary susceptibility into a state-dependent linewidth. These results identify engineered dissipation as an information-carrying resource for fast quantum non-demolition readout.

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Yiming Yu, Xinyu Zhao, Jia-Wen Yu, Ke-Xiong Yan, Wei Qin, Ye-Hong Chen, Yan Xia, Franco Nori. 2026-06-30. Qubit Readout via State-Dependent Radiative Linewidths. https://arxiv.org/abs/2606.31011

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