Bragg-Reflection Waveguides as Practical Photon-Pair Sources for Quantum Rangefinding

Photon pairs generated via spontaneous parametric down-conversion (SPDC) are a crucial resource in the development of quantum protocols and quantum technologies, due to the strong correlation between two photons of the same pair. Efficient pair generation is necessary for protocols that require high signal-to-noise ratios when embedded in a lossy and noisy environment. Nonlinear waveguides are well-established platforms for photon pair generation. However, scattering and material absorption can inhibit the efficiency of the pair generation and require high pump powers. Here, we present an aluminum gallium arsenide Bragg-reflection waveguide, fabricated following an optimized recipe, that shows a record brightness compared to other samples with the same structure. When pumped with a sub-mW continuous wave laser, our waveguide generates photon pairs at a rate of $340\,\mathrm{k}\mathrm{Hz}\cdot \mathrm{m}\mathrm{W}^{-1}$, and a spectral width of $100\,\mathrm{n}\mathrm{m}$ in the telecom band. As a direct application, we investigate the operation of our waveguide in quantum rangefinding, a quantum protocol that employs time correlations between photon pairs to measure objects' distances, while camouflaging within background. This protocol was implemented with nonlinear crystals engineered for broadband emission. Supported by simulations of signal-to-noise ratio, we introduce our low-loss and broadband waveguide as a novel platform for telecom quantum rangefinding, robust against loss and noise.