Compact narrowband photon-pair generation by slow-light spectral engineering

TL;DR

This paper proposes a novel integrated photonic approach using intra-cavity slow light in erbium-doped lithium niobate microrings to generate narrowband photon pairs with high purity and efficiency, suitable for quantum networking.

Contribution

Introducing a slow-light spectral engineering method within integrated microrings to produce narrowband photon pairs compatible with quantum systems.

Findings

Achieved high single photon purity and heralding efficiency in integrated devices.

Demonstrated the feasibility of using erbium-doped thin-film lithium niobate microrings for narrowband photon generation.

Showed that spectral filtering via slow light enhances photon pair quality without reducing brightness.

Abstract

Efficiently generating photon pairs with high heralding efficiency and high single photon purity that are bandwidth matched to quantum emitters, quantum memories, and other matter-based qubits is critical for quantum networking applications. However, nonlinear optics-based sources require substantial spectral engineering to overcome the orders of magnitude bandwidth mismatch between those sources and qubit systems. A popular solution is cavity-enhanced spontaneous parametric down conversion (SPDC) where the cavity sets the photon bandwidth and simultaneously enhances the spectral brightness of the SPDC. Bulk, free-space configurations are generally required to achieve the MHz-scale bandwidths required to interface with most qubit systems. Replicating these in scalable integrated photonic architectures is an ongoing challenge due to the much higher propagation losses that limit the size and linewidth of chip-based resonators. We show here how an intra-cavity slow light medium, acting as an ultra-narrow filter, would enable narrowband photon pair generation in broadband cavities with high single photon purity and without compromising the heralding efficiency. We show that such metrics can be readily realized in erbium doped thin-film lithium niobate microrings using realistic design parameters.