High-purity frequency-degenerate photon pair generation via cascaded SFG/SPDC in thin film lithium niobate

TL;DR

This paper introduces a dual-pump scheme in thin film lithium niobate waveguides to generate high-purity, frequency-degenerate photon pairs with suppressed noise, advancing scalable quantum photonics.

Contribution

The authors propose and experimentally validate a cascaded SFG/SPDC method that enhances photon pair purity and simplifies device design compared to microresonator approaches.

Findings

Achieved a photon pair brightness of 1.0(3)×10^5 Hz/nm/mW.

Demonstrated 40 dB suppression of parasitic single-pump processes.

Validated the approach in a layer-poled thin film lithium niobate waveguide.

Abstract

Frequency-degenerate photon pairs generated using nonlinear photonic integrated devices are a crucial resource for scalable quantum information processing and metrology. However, their realization is hindered by unwanted parametric processes occurring within the same phase matching band, which degrade the signal-to-noise ratio and reduce the purity of the associated quantum states. Here, we propose a dual-pump scheme to produce frequency-degenerate photon pairs, based on cascaded sum-frequency generation and spontaneous parametric down-conversion occurring within a single waveguide, while strongly suppressing parasitic photon pair generation from single-pump processes. This approach significantly simplifies the design compared to microresonator-based methods and enables both pumping and collection of photon pairs entirely in the telecom band. We experimentally validate the concept in a layer-poled thin film lithium niobate waveguide, achieving frequency-degenerate photon pair generation with a brightness of \SI{1.0(3)e5}{\hertz \per \nm \per \square \milli \watt } and a 40 dB suppression of unwanted single-pump processes.