Bell state analyzer for spectrally distinct photons

TL;DR

This paper presents a novel Bell state analyzer that can distinguish frequency-bin Bell states of spectrally distinct photons using electro-optic modulation and pulse shaping, achieving high accuracy without requiring spectral indistinguishability.

Contribution

The authors introduce a quantum frequency processor that implements interleaved Hadamard gates to analyze Bell states directly on frequency mismatch, enabling high-fidelity measurements of spectrally distinct photons.

Findings

Achieved approximately 98% accuracy in Bell state discrimination

Demonstrated operation on frequency-mismatched entangled photons

Resolved the challenge of spectral distinguishability in Bell state analysis

Abstract

We demonstrate a Bell state analyzer that operates directly on frequency mismatch. Based on electro-optic modulators and Fourier-transform pulse shapers, our quantum frequency processor design implements interleaved Hadamard gates in discrete frequency modes. Experimental tests on entangled-photon inputs reveal accuracies of $\sim$98\% for discriminating between the $|\Psi^+\rangle$ and $|\Psi^-\rangle$ frequency-bin Bell states. Our approach resolves the tension between wavelength-multiplexed state transport and high-fidelity Bell state measurements, which typically require spectral indistinguishability.