Degenerate photons from a cryogenic spontaneous parametric down-conversion source

<p>Dataset of the publication &quot;Degenerate photons from a cryogenic spontaneous parametric down-conversion source&quot;,&nbsp;N. A. Lange,&nbsp;T. Schapeler, J. P. H&ouml;pker, M. Protte, and T. J. Bartley, <a href="https://doi.org/10.48550/arXiv.2303.17428">https://doi.org/10.48550/arXiv.2303.17428</a>&nbsp;(2023).</p> <p>&nbsp;</p> <p>Abstract:</p> <blockquote> <p>We demonstrate the generation of degenerate photon pairs from spontaneous parametric down-conversion in titanium-indiffused waveguides in lithium niobate at cryogenic temperatures. Since the phase matching cannot be temperature tuned inside a cryostat, we rely on a precise empirical model of the refractive indices when fabricating a fixed poling period. We design the phase-matching properties of our periodic poling to enable signal and idler photons at 1559.3(6) nm and characterize the indistinguishability of our photons by performing a Hong-Ou-Mandel interference measurement. Despite the effects of photorefraction and pyroelectricity, which can locally alter the phase matching, we achieve cryogenic indistinguishable photons within 1.5 nm of our design wavelength. Our results verify sufficient understanding and control of the cryogenic nonlinear process, which&nbsp;has wider implications when combining quasi-phase-matched nonlinear optical processes with other cryogenic photonic quantum technologies, such as superconducting detectors.</p> </blockquote>