Distinguishability and mixedness in quantum interference

Abstract

We study the impact of distinguishability and mixedness -two fundamental properties of quantum states -on quantum interference. We show that these can influence the interference of multiple particles in different ways, leading to effects that cannot be observed in the interference of two particles alone. This is demonstrated experimentally by interfering three independent photons in pure and mixed states and observing their different multiphoton interference, despite exhibiting the same two-photon Hong-Ou-Mandel (HOM) interference. Besides its fundamental relevance, our observation has important implications for quantum technologies relying on photon interference.

Quantum circuits for measuring weak values, Kirkwood–Dirac quasiprobability distributions, and state spectra

“…These results bring proof-of-principle tests of the nonclassicality of quantum theory-a vital resource for information processing-closer to current experimental capabilities. Indirect measurements of unitary invariants up to fourth order have been made in different platforms [71,129,130]. We believe that the unified view of nonclassicality we discussed here may boost the interest in a systematic exploration of nonclassicality witnessed and quantified by unitary invariants.…”

“…Bargmann invariants play an important role in linear optics [71], characterizing multiphoton interference. In the context of invariant theory, multivariate traces of the form Tr(X 1 .…”