Making entangled photons indistinguishable by a time lens

TL;DR

This paper introduces a quantum temporal imaging technique using a time lens to restore the indistinguishability of entangled photons from parametric down-conversion, enhancing quantum interference visibility.

Contribution

It demonstrates that a time lens can be used to perfectly restore photon indistinguishability and maximize Hong-Ou-Mandel interference visibility.

Findings

Time lens restores photon indistinguishability

Achieves 100% Hong-Ou-Mandel visibility

Effective with high group delay dispersion

Abstract

We propose an application of quantum temporal imaging to restoring the indistinguishability of the signal and the idler photons produced in type-II spontaneous parametric down-conversion with a pulsed broadband pump. It is known that in this case, the signal and the idler photons have different spectral and temporal properties. This effect deteriorates their indistinguishability and the visibility of the Hong-Ou-Mandel interference, respectively. We demonstrate that inserting a time lens in one arm of the interferometer and choosing properly its magnification factor restores perfect indistinguishability of the signal and the idler photons and provides 100\% visibility of the Hong-Ou-Mandel interference in the limit of high focal group delay dispersion of the time lens.