Observation of detection-dependent multi-photon coherence times

TL;DR

This paper demonstrates that multi-photon coherence times depend on the number of photons and detection scheme, revealing higher-order indistinguishability effects that influence interference visibility in quantum experiments.

Contribution

It introduces the concept that multi-photon coherence times are measurement-dependent and influenced by higher-order indistinguishability, a novel insight in quantum interference analysis.

Findings

Multi-photon coherence time varies with photon number and detection scheme.

Higher-order effects in indistinguishability affect interference visibility.

Optimal quantum interferometry requires suitable detection strategies.

Abstract

The coherence time constitutes one of the most critical parameters that determines whether or not interference is observed in an experiment. For photons, it is traditionally determined by the effective spectral bandwidth of the photon. Here we report on multi-photon interference experiments in which the multi-photon coherence time, defined by the width of the interference signal, depends on the number of interfering photons and on the measurement scheme chosen to detect the particles. A theoretical analysis reveals that all multi-photon interference with more than two particles features this dependence, which can be attributed to higher-order effects in the mutual indistinguishability of the particles. As a striking consequence, a single, well-defined many-particle quantum state can exhibit qualitatively different degrees of interference, depending on the chosen observable. Therefore, optimal sensitivity in many-particle quantum interferometry can only be achieved by choosing a suitable detection scheme.