Witnesses of coherence and dimension from multiphoton indistinguishability tests
Taira Giordani, Chiara Esposito, Francesco Hoch, Gonzalo Carvacho, Daniel J. Brod, Ernesto F. Galvão, Nicolò Spagnolo, Fabio Sciarrino · Physical Review Research · 2021
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 type of coherence witness that uses pairwise state comparisons to identify superpositions in a basis-independent way.Our experiment uses a single interferometric setup to simultaneously measure the three pairwise overlaps among three single-photon states via Hong-Ou-Mandel tests.Aside from 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.