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arXiv:2510.08386 · Physical Review A

Optimal quantum spectroscopy using single-photon pulses

Sourav Das, Aiman Khan, Francesco Albarelli, Animesh Datta

Published Feb 24, 2026• 1 citation
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Abstract

We provide the ultimate precision attainable in spectroscopy of a quantum emitter using single-photon pulses. We find that the maximum precision of linewidth estimation is independent of the details of the emitter's bare Hamiltonian, though this is not true for the detunings. We also identify optimal pulse shapes attaining these precisions.

DOI
10.1103/dv49-gwsb

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We provide the ultimate precision attainable in spectroscopy of a quantum emitter using single-photon pulses. We find that the maximum precision of linewidth estimation is independent of the details of the emitter's bare Hamiltonian, though this is not true for the detunings. We also identify optimal pulse shapes attaining these precisions.
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We analytically derive the quantum state of a single-photon pulse scattered from a single quantum two-level emitter interacting with a vibrational bath. This solution for the quadripartite system enables an information-theoretic characterization of vibrational effects in quantum light spectroscopy. We show that vibration-induced dephasing reduces the quantum Fisher information (QFI) for estimating the emitter's linewidth, largely reflecting the Franck-Condon suppression of light-matter coupling. Comparing time- and frequency-resolved photodetection, we find the latter to be more informative in estimating the emitter's linewidth for stronger vibrational coupling.
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Cavity-enhanced spectroscopy is a widely used experimental technique. We show that detuning the cavity frequency from the transition of interest can enhance the precision for dipole moment estimation by up to two orders of magnitude beyond the improvement when the cavity is resonant with the transition. We show this for both classical continuous-wave (CW) and pulsed single-photon probes, even in the presence of losses. We trace this enhancement to a detuning-controlled redistribution of information between the light- and matter-like polaritons, with losses determining the optimal branch. We show that this enhancement remains accessible using conventional photodetection and time-correlated single-photon counting.