Degenerate Photons from a Cryogenic Spontaneous Parametric Down-Conversion Source

We demonstrate the generation of degenerate photon pairs from spontaneous parametric down-conversion in titanium in-diffused 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 $\pm$ 0.6) 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 to our design wavelength. Our results verify sufficient understanding and control of the cryogenic nonlinear process, which has wider implications when combining quasi-phase-matched nonlinear optical processes with other cryogenic photonic quantum technologies, such as superconducting detectors.Comment: 7 pages, 6 figure

Pyroelectric influence on lithium niobate during the thermal transition for cryogenic integrated photonics

Lithium niobate has emerged as a promising platform for integrated quantum optics, enabling efficient generation, manipulation, and detection of quantum states of light. However, integrating single-photon detectors requires cryogenic operating temperatures, since the best performing detectors are based on narrow superconducting wires. While previous studies have demonstrated the operation of quantum light sources and electro-optic modulators in LiNbO _3 at cryogenic temperatures, the thermal transition between room temperature and cryogenic conditions introduces additional effects that can significantly influence device performance. In this paper, we investigate the generation of pyroelectric charges and their impact on the optical properties of lithium niobate waveguides when changing from room temperature to 25 K, and vice versa. We measure the generated pyroelectric charge flow and correlate this with fast changes in the birefringence acquired through the Sénarmont-method. Both electrical and optical influence of the pyroelectric effect occur predominantly at temperatures above 100 K

Dataset: Pyroelectric Influence on Lithium Niobate During the Thermal Transition for Cryogenic Integrated Photonics

<p>Dataset of the publication "Pyroelectric Influence on Lithium Niobate During the Thermal Transition for Cryogenic Integrated Photonics", F. Thiele, et al., in the journal Materials for Quantum Technology (2023).</p> <p>Abstract:</p> <blockquote> <p>Lithium niobate has emerged as a promising platform for integrated quantum optics, enabling efficient generation, manipulation, and detection of quantum states of light. However, integrating single-photon detectors requires cryogenic operating temperatures, since the best performing detectors are based on narrow superconducting wires. While previous studies have demonstrated the operation of quantum light sources and electro-optic modulators in LiNbO<sub>3</sub> at cryogenic temperatures, the thermal transition between room temperature and cryogenic conditions introduces additional effects that can significantly influence device performance. In this paper, we investigate the generation of pyroelectric charges and their impact on the optical properties of lithium niobate waveguides when changing from room temperature to 25 K, and vice versa. We measure the generated pyroelectric charge flow and correlate this with fast changes in the birefringence acquired through the Sénarmont-method. Both electrical and optical influence of the pyroelectric effect occur predominantly at temperatures above 100 K.</p> </blockquote>This work was supported by the Bundesministerium f ̈ur Bildung und Forschung (Grant No. 13N14911) and the Deutsche Forschungsgemeinschaft (231447078–TRR 142)