Scaling-Enhanced Rapid Readout of a Qubit Ensemble Assisted by High-Frequency Detector Modes
Quantum measurements of large qubit ensembles are often performed indirectly by coupling the ensemble to a detector and subsequently measuring the detector. Despite the importance of rapid collective readout, it remains unclear what determines how the readout time scales with the number of qubits $N$. Here, we first establish a benchmark $N^{-1/2}$ for a broad class of detectors without ultraviolet high-frequency modes. We then show that the detector with unbounded high-frequency modes can surpass this benchmark and yield a characteristic time scaling $N^{-1/(2-ν)}$ for $0 < ν< 2$, where $ν$ characterizes the spectral structure of the detector. Our results establish high-frequency detector modes as a resource for achieving a scaling advantage in collective quantum readout, with the detector spectrum directly controlling the scaling exponent of the readout time.