Tests of quantum mechanics based on interference of photons

Sascha Agne, Thomas Kauten, Jeongwan Jin +6 more

Multiparticle quantum interference is critical for our understanding and exploitation of quantum information, and for fundamental tests of quantum mechanics. A remarkable example of multi-partite correlations is exhibited by the Greenberger-Horne-Zeilinger (GHZ) state. In a GHZ state, three particles are correlated while no pairwise correlation is found. The manifestation of these strong correlations in an interferometric setting has been studied theoretically since 1990 but no three-photon GHZ interferometer has been realized experimentally. Here we demonstrate three-photon interference that does not originate from two-photon or single photon interference. We observe phase-dependent variation of three-photon coincidences with (92.7±4.6)% visibility in a generalized Franson interferometer using energy-time entangled photon triplets. The demonstration of these strong correlations in an interferometric setting provides new avenues for multiphoton interferometry, fundamental tests of quantum mechanics, and quantum information applications in higher dimensions.

Peter Shadbolt, Jonathan C. F. Mathews, Anthony Laing +1 more

Urbasi Sinha, Christophe Couteau, Fay Dowker B +3 more

As one of the postulates of quantum mechanics, Born's rule tells us how to get probabilities for experimental outcomes from the complex wave function of the system. Its quadratic nature entails that interference occurs in pairs of paths. We present an experiment that sets out to test the correctness of Born's rule by testing for the presence or absence of genuine three-path interference. This is done using single photons and a three slit aperture.

Rainer Kaltenbaek, B. Blauensteiner, Markus Aspelmeyer +1 more

Kevin Randles, S. J. van Enk

We analyze the interference of individual photons in two overlapping Mach–Zehnder interferometers joined via a common beam splitter. We show how two kinds of interference effects—single-photon Mach–Zehnder interference and two-photon Hong–Ou–Mandel interference—interfere with one another, partially canceling each other out. This configuration illustrates how quantum effects can combine nontrivially and, moreover, emphasizes that quantum interference happens at measurement. This work can serve as a bridge to more advanced quantum mechanical concepts, such as testing the predictions of quantum mechanics vs local realism.

Urbasi Sinha, Debadrita Ghosh