Effects of coherence on temporal resolution

TL;DR

This paper experimentally investigates how optical coherence influences the precision of estimating temporal separation between two single-photon pulses, demonstrating that coherent mode projections are optimal regardless of coherence level.

Contribution

It clarifies the role of coherence in mode projections for quantum metrology, showing they are optimal across all coherence levels.

Findings

Coherent mode projections are optimal for any degree of coherence.

Proper normalization of quantum Fisher information is essential for accurate interpretation.

Experimentally demonstrates the advantage of mode projections in temporal separation estimation.

Abstract

Measuring small separations between two optical sources, either in space or in time, constitute an important metrological challenge as standard intensity-only measurements fail for vanishing separations. Contrarily, it has been established that appropriate coherent mode projections can appraise arbitrarily small separations with quantum-limited precision. However, the question of whether the optical coherence brings any metrological advantage to mode projections is still a point of debate. Here, we elucidate this problem by experimentally investigating the effect of varying coherence on estimating the temporal separation between two single-photon pulses. We show that, for an accurate interpretation, special attention must be paid to properly normalize the quantum Fisher information to account for the strength of the signal. Our experiment demonstrates that coherent mode projections are optimal for any degree of coherence.