Witnesses of coherence and dimension from multiphoton indistinguishability tests

TL;DR

This paper introduces a novel, basis-independent coherence witness using pairwise state comparisons via Hong-Ou-Mandel tests, demonstrating its effectiveness in assessing quantum coherence and Hilbert-space dimension in a single interferometric setup.

Contribution

It presents an experimental method for a new type of coherence witness based on pairwise state comparisons, applicable in a basis-independent manner.

Findings

Effective coherence detection through pairwise overlaps

Simultaneous measurement of coherence and dimension witnesses

Single interferometric setup simplifies quantum state analysis

Abstract

Quantum coherence marks a deviation from classical physics, and has been studied as a resource for metrology and quantum computation. Finding reliable and effective methods for assessing its presence is then highly desirable. Coherence witnesses rely on measuring observables whose outcomes can guarantee that a state is not diagonal in a known reference basis. Here we experimentally measure a novel type of coherence witness that uses pairwise state comparisons to identify superpositions in a basis-independent way. Our experiment uses a single interferometric set-up to simultaneously measure the three pairwise overlaps among three single-photon states via Hong-Ou-Mandel tests. Besides coherence witnesses, we show the measurements also serve as a Hilbert-space dimension witness. Our results attest to the effectiveness of pooling many two-state comparison tests to ascertain various relational properties of a set of quantum states.