Frequency-Bin Entanglement of Ultra-Narrow Band Non-Degenerate Photon Pairs

TL;DR

This paper demonstrates frequency-bin entanglement between ultra-narrowband, non-degenerate photon pairs generated via cavity-enhanced spontaneous parametric down conversion, and shows their compatibility with quantum memories and violation of Bell inequalities.

Contribution

It introduces a method to generate and verify frequency-bin entangled photon pairs compatible with quantum memories, including a Bell test demonstration.

Findings

High-visibility two-photon interference observed.

Successful violation of the CH Bell inequality.

Compatibility with praseodymium-based quantum memories demonstrated.

Abstract

We demonstrate frequency-bin entanglement between ultra-narrowband photons generated by cavity enhanced spontaneous parametric down conversion. Our source generates photon pairs in widely non-degenerate discrete frequency modes, with one photon resonant with a quantum memory material based on praseodymium doped crystals and the other photon at telecom wavelengths. Correlations between the frequency modes are analyzed using phase modulators and narrowband filters before detection. We show high-visibility two photon interference between the frequency modes, allowing us to infer a coherent superposition of the modes. We develop a model describing the state that we create and use it to estimate optimal measurements to achieve a violation of the Clauser-Horne (CH) Bell inequality under realistic assumptions. With these settings we perform a Bell test and show a significant violation of the CH inequality, thus proving the entanglement of the photons. Finally we demonstrate the compatibility with a quantum memory material by using a spectral hole in the praseodymium (Pr) doped crystal as spectral filter for measuring high-visibility two-photon interference. This demonstrates the feasibility of combining frequency-bin entangled photon pairs with Pr-based solid state quantum memories.