A ultrabright, two-colour photon pair source based on thin-film lithium niobate for bridging visible and telecom wavelengths

TL;DR

This paper reports a highly efficient, integrated photon pair source in thin-film lithium niobate that links visible and telecom wavelengths, with exceptional spectral brightness and photon quality, advancing quantum communication technology.

Contribution

The work introduces a novel, high-brightness, non-degenerate photon pair source in thin-film lithium niobate with superior spectral and quantum properties compared to previous waveguide-based sources.

Findings

Heralded second-order correlation function as low as 6.7e-3

Spectral brightness of 0.44e7 pairs/s/mW/GHz

High spectral purity and agreement with theoretical bandwidth

Abstract

We present the design and characterisation of a guided-wave, bright and highly frequency non-degenerate parametric down-conversion source in thin-film lithium niobate. The source generates photon pairs with wavelengths of 815$\,\mathrm{nm}$ and 1550$\,\mathrm{nm}$ linking the visible wavelength regime with telecommunication wavelengths. We confirm the high quality of the generated single photons by determining a value for the heralded second-order correlation function as low as $g^{(2)}_h(0) = (6.7\pm1.1)\cdot10^{-3}$. Furthermore, we achieve a high spectral brightness of 0.44$\cdot$10$^{7}$$\frac{\text{pairs}}{\text{s} \cdot \text{mW} \cdot \text{GHz}}$ which is two orders of magnitude higher than sources based on weakly guiding waveguides. The almost perfect sinc-shape and the strong agreement between the effective and nominal bandwidth highlights the success of our integrated workflow, which begins with device design and continues through precise fabrication to detailed quantum-state characterization. This comprehensive approach enables targeted optimization of the source, resulting in excellent quantum state generation. Our results set a new standard for on-chip, non-degenerate photon-pair sources and represent a crucial step towards practical, scalable quantum communication networks and photonic quantum computing.