Coherent frequency bridge between visible and telecommunications band of vortex light

TL;DR

This paper demonstrates a coherent frequency bridge for vortex light between visible and infrared wavelengths using difference frequency conversion, enabling high-fidelity quantum state transfer in high-dimensional quantum networks.

Contribution

It introduces a novel coherent OAM frequency conversion method connecting visible and infrared wavelengths with high efficiency and fidelity for quantum communication.

Findings

Maximum quantum conversion efficiency of 36% for topological charge 0.

Average fidelity of 96.51% for infrared OAM state.

OAM conservation confirmed through interference measurements.

Abstract

In quantum communications, vortex photons can encode higher-dimensional quantum states and build high-dimensional communication networks (HDCNs). The interfaces that connect different wavelengths are significant in HDCNs. We construct a coherent orbital angular momentum (OAM) frequency bridge via difference frequency conversion in a nonlinear bulk crystal for HDCNs. Using a single resonant cavity, maximum quantum conversion efficiencies from visible to infrared are 36\%, 15\%, and 7.8\% for topological charges of 0,1, and 2, respectively. The average fidelity obtained using quantum state tomography for the down-converted infrared OAM-state of topological charge 1 is 96.51\%. We also prove that the OAM is conserved in this process by measuring visible and infrared interference patterns. This coherent OAM frequency-down conversion bridge represents a basis for an interface between two high-dimensional quantum systems operating with different spectra.