Implementing two-photon interference in the frequency domain with electro-optic phase modulators

TL;DR

This paper demonstrates high-visibility two-photon interference in the frequency domain using electro-optic modulators, showing potential for quantum communication in telecom fibers and validating theoretical models with experimental results.

Contribution

It introduces a theoretical framework and experimental validation for frequency-domain two-photon interference, including Bell inequality optimization and classical-quantum equivalence.

Findings

Raw visibility of interference exceeds 99%

Violation of CH74 inequality by over 18 standard deviations

Theoretical expression accurately predicts experimental results

Abstract

Frequency-entangled photons can be readily produced using parametric down-conversion. We have recently shown how such entanglement could be manipulated and measured using electro-optic phase modulators and narrow-band frequency filters, thereby leading to two-photon interference patterns in the frequency domain. Here we introduce new theoretical and experimental developments showing that this method is potentially a competitive platform for the realization of quantum communication protocols in standard telecommunication fibres. We derive a simple theoretical expression for the coincidence probabilities and use it to optimize a Bell inequality. Furthermore, we establish an equivalence between the entangled- photon scheme and a classical interference scheme. Our measurements of two-photon interference in the frequency domain yield raw visibilities in excess of 99%. We use our high quality setup to experimentally validate the theoretical predictions, and in particular we report a violation of the CH74 inequality by more than 18 standard deviations.