High-Precision Measurement of Time Delay with Frequency-Resolved Hong-Ou-Mandel Interference of Weak Coherent States

TL;DR

This paper presents a novel frequency-resolved Hong-Ou-Mandel interference scheme for high-precision time delay measurements using weak coherent states, achieving uncertainties around 10 ps even for delays much longer than the coherence time.

Contribution

It introduces a new frequency-resolved HOM measurement method that surpasses conventional techniques in precision, validated by experimental results and quantum estimation theory.

Findings

Achieved ~10 ps uncertainty in time delay measurements.

Demonstrated effectiveness for delays up to 4 ps longer than coherence time.

Experimental results agree with theoretical predictions.

Abstract

We demonstrate a scheme for high-precision measurements of time delay based on frequency-resolved Hong-Ou-Mandel (HOM) interference. Our approach is applied to weak coherent states and exploits an array of single-photon avalanche diodes (SPADs). Unlike conventional HOM experiments, our setup enables high-precision measurements producing an uncertainty per coincidence of about $\sim 10$ ps even for photons separated by delays up to $\sim 4$ ps so much greater than their coherence time where ordinary non-resolved HOM fails. This result confirms our newly developed theoretical predictions that consider, differently from previous theoretical results, a finite frequency resolution in the detection. We compare the performance of this scheme against the conventional non-resolved case. Experimental data align well with the predictions of quantum estimation theory, demonstrating a significant reduction in the uncertainty. Due to the physics of the frequency-resolved HOM effect, the gain in precision is particularly high when the estimated time delay is much longer than the coherence time.