Fiber-based photon-pair source capable of hybrid entanglement in frequency and transverse mode, controllably scalable to higher dimensions

TL;DR

This paper presents a fiber-based photon-pair source that generates hybrid entanglement in frequency and transverse mode, with scalable higher-dimensional entanglement enabled by multiple simultaneous SFWM processes in a few-mode fiber.

Contribution

The work introduces a novel fiber-based source design that supports multiple, nearly-factorable SFWM processes for scalable hybrid entanglement in frequency and transverse mode.

Findings

Supports multiple simultaneous SFWM processes with distinct transverse modes

Achieves nearly-factorable joint spectral amplitudes for each process

Enables scalable higher-dimensional entanglement through mode control

Abstract

We have designed and implemented a photon-pair source, based on the spontaneous four wave mixing (SFWM) process in a few-mode fiber, in a geometry which permits multiple, simultaneous SFWM processes, each associated with a distinct combination of transverse modes for the four participating waves. In our source: i) each process is group-velocity-matched so that it is, by design, nearly-factorable, and ii) the spectral separation between neighboring processes is greater than the marginal spectral width of each process. Consequently, there is a direct correspondence between the joint amplitude of each process and each of the Schmidt mode pairs of the overall two-photon state. Our approach permits hybrid entanglement in discrete frequency and in transverse mode, whereby control of the number of supported fiber transverse modes allows scalability to higher dimensions while spectral filtering may be used for straightforward Schmidt mode discrimination.