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

## TL;DR

This paper demonstrates two-photon interference effects with polarization-entangled photons in a Franson interferometer, revealing phase-insensitive interference fringes and recovering polarization entanglement from unentangled inputs.

## Contribution

It introduces a novel polarization-based Franson interferometer setup that exhibits phase-insensitive interference and enables entanglement recovery from unentangled photons.

## Key findings

- Observation of Hong-Ou-Mandel type interference fringes without a common beamsplitter
- Measurement of spatial quantum beating fringes for nondegenerate photon pairs
- Successful recovery of polarization entanglement from unentangled photon inputs

## Abstract

We present two-photon interference experiments with polarization-entangled photon pairs in a polarization-based Franson-type interferometer. Although the two photons do not meet at a common beamsplitter, a phase-insensitive Hong-Ou-Mandel type two-photon interference peak and dip fringes are observed, resulting from the two-photon interference effect between two indistinguishable two-photon probability amplitudes leading to a coincidence detection. A spatial quantum beating fringe is also measured for nondegenerate photon pairs in the same interferometer, although the two-photon states have no frequency entanglement. When unentangled polarization-correlated photons are used as an input state, the polarization entanglement is successfully recovered through the interferometer via delayed compensation.

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Source: https://tomesphere.com/paper/1706.03594