Experimental position-time entanglement with degenerate single photons

TL;DR

This paper demonstrates position-time entanglement between degenerate single photons that never physically meet, using a fiber-optic interferometer to observe interference effects analogous to traditional entanglement experiments.

Contribution

It introduces an experimental setup showing entanglement-like interference with photons that do not interact directly, expanding the understanding of quantum entanglement in photonic systems.

Findings

Wavefunction overlaps up to 94% measured

Interference observed with photons traveling in opposite directions

Experiment analogous to Franson-type entanglement

Abstract

We report an experiment in which two-photon interference occurs between degenerate single photons that never meet. The two photons travel in opposite directions through our fibre-optic interferometer and interference occurs when the photons reach two different, spatially separated, 2-by-2 couplers at the same time. We show that this experiment is analogous to the conventional Franson-type entanglement experiment where the photons are entangled in position and time. We measure wavefunction overlaps for the two photons as high as 94 $\pm$ 3%.