Physical Review Research (Apr 2021)

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

DOI
https://doi.org/10.1103/PhysRevResearch.3.023031
Journal volume & issue
Vol. 3, no. 2
p. 023031

Abstract

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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.