Two-photon interference of temporally separated photons

Abstract

We present experimental demonstrations of two-photon interference involving temporally separated photons within two types of interferometers: a Mach-Zehnder interferometer and a polarization-based Michelson interferometer. The two-photon states are probabilistically prepared in a symmetrically superposed state within the two interferometer arms by introducing a large time delay between two input photons; this state is composed of two temporally separated photons, which are in two different or the same spatial modes. We then observe two-photon interference fringes involving both the Hong-Ou-Mandel interference effect and the interference of path-entangled two-photon states simultaneously in a single interferometric setup. The observed two-photon interference fringes provide simultaneous observation of the interferometric properties of the single-photon and two-photon wavepackets. The observations can also facilitate a more comprehensive understanding of the origins of the interference phenomena arising from spatially bunched/anti-bunched two-photon states comprised of two temporally separated photons within the interferometer arms.

Experimental interference of uncorrelated photons

“…1, two types of number-correlated two-photon states are generated with equal probability in the two interferometer arms beyond the 50:50 beamsplitter (BS1). One is the state wherein the two input photons follow two different paths 1 and 2, expressed as BS1 [27][28][29][30]39 . Moreover, they can differ in terms of external degrees of freedom, such as the input spatial modes and the arrival time of the two incident photons at BS1 30,39,40 .…”

The Quantum Regime Operation of Beam Splitters and Interference Filters

“…Similar expectation values may be derived for any combination of any two interference patterns, one from each photodetector, e.g. [24][25][26]. It is noteworthy that the phases of the spontaneously emitted photons do not appear in the conventional quantum descriptions of two-photon beats, e.g.…”

“…It is noteworthy that the phases of the spontaneously emitted photons do not appear in the conventional quantum descriptions of two-photon beats, e.g. [22][23][24][25][26].…”

Two-photon interference of polarization-entangled photons in a Franson interferometer

“…Typically, Feynman-like path diagrams for the two possible processes at the BS have been used to explain two-photon interference effects, especially for HOM-type experiments 18,19 . This approach can also be applied to explicate various quantum interference experiments employing correlated photons and using Mach-Zehnder and Michelson interferometers 20,21 .…”

“…To date, HOM-type two-photon interference fringes have only been observed when the two input photons are mixed at a common BS, regardless of whether the two photons meet simultaneously at the BS 1,18,21 . This invites the question of whether the HOM-type fringe pattern can be observed without using a common BS.…”