Direct generation of frequency-bin entangled photons via two-period quasi-phase-matched parametric downconversion

TL;DR

This paper presents a straightforward method for generating frequency-bin entangled photon pairs using a specially fabricated nonlinear crystal with two poling periods, enabling direct entanglement in discrete frequency modes for advanced quantum information processing.

Contribution

The authors introduce a novel two-period quasi-phase-matched crystal design that directly produces frequency-bin entangled photons and demonstrates mode conversion to polarization, enhancing quantum communication capabilities.

Findings

High-visibility Hong-Ou-Mandel interference observed

Successful deterministic conversion from frequency-bin to polarization modes

Potential for generating high-dimensional frequency-bin entanglement

Abstract

We report a simple scheme for direct generation of frequency-bin entangled photon pairs via spontaneous parametric downconversion. Our fabricated nonlinear optical crystal with two different poling periods can simultaneously satisfy two different, spectrally symmetric nondegenerate quasi-phase-matching conditions, enabling the direct generation of entanglement in two discrete frequency-bin modes. Our produced photon pairs exhibited Hong-Ou-Mandel interference with high-visibility beating oscillations, a signature of two-mode frequency-bin entanglement. Moreover, we demonstrate deterministic entanglement-mode conversion from frequency-bin to polarization modes, with which our source can be more versatile for various quantum applications. Our scheme can be extended to direct generation of high-dimensional frequency-bin entanglement, and thus will be a key technology for frequency-multiplexed optical quantum information processing.