Quantum-limited time-frequency estimation through mode-selective photon measurement

TL;DR

This paper demonstrates quantum-limited precision in estimating time and frequency separations of signals using mode-selective measurements, surpassing classical bounds by employing shaped ultrafast pulses and sum-frequency generation.

Contribution

It extends mode-selective quantum measurement techniques to the time-frequency domain, achieving unprecedented resolution and precision in separating incoherent signals.

Findings

Resolved temporal and spectral separations ten times smaller than bandwidths.

Achieved ten-fold improvement over classical intensity-based bounds.

Validated quantum-limited estimation in the time-frequency domain.

Abstract

By projecting onto complex optical mode profiles, it is possible to estimate arbitrarily small separations between objects with quantum-limited precision, free of uncertainty arising from overlapping intensity profiles. Here we extend these techniques to the time-frequency domain using mode-selective sum-frequency generation with shaped ultrafast pulses. We experimentally resolve temporal and spectral separations between incoherent mixtures of single-photon level signals ten times smaller than their optical bandwidths with a ten-fold improvement in precision over the intensity-only Cram\'er-Rao bound.