Complete frequency-bin Bell basis synthesizer

TL;DR

This paper demonstrates a versatile, turnkey method for generating all four frequency-bin Bell states using standard telecommunication equipment, with high fidelity and potential for sensing applications.

Contribution

It introduces a novel setup for complete frequency-bin Bell state synthesis with high fidelity, utilizing spectral pumping and Bayesian state reconstruction.

Findings

Achieved fidelities ≥97% for all Bell states

Demonstrated sensitivity to temporal delays in frequency-bin states

Enabled potential for enhanced resolution and nonlocal sensing

Abstract

We report the experimental generation of all four frequency-bin Bell states in a single versatile setup via successive pumping of spontaneous parametric downconversion with single and dual spectral lines. Our scheme utilizes intensity modulation to control the pump configuration and offers turn-key generation of any desired Bell state using only off-the-shelf telecommunication equipment. We employ Bayesian inference to reconstruct the density matrices of the generated Bell states, finding fidelities $\geq$ 97% for all cases. Additionally, we demonstrate the sensitivity of the frequency-bin Bell states to common-mode and differential-mode temporal delays traversed by the photons comprising the state$\unicode{x2013}$presenting the potential for either enhanced resolution or nonlocal sensing enabled by our complete Bell basis synthesizer.