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Applied Optics

Development of a frequency-stabilized pump source at 436 nm for 606 nm–1.5 µm entangled photon pair generation

Rina Takeda, Shinnosuke Aoyama, Kyosuke Sato, Feng-Lei Hong, Tomoyuki Horikiri, Daisuke Akamatsu

Published Sep 3, 2025• 0 citations
Publisher

Abstract

We developed a frequency-stable laser light source operating at 436 nm to produce entangled photon pairs at 606 nm and 1.5 µm via spontaneous parametric down conversion. This light source was produced via the sum frequency generation of two lasers operating at 852 and 895 nm, each stabilized to the D2 and D1 transitions of cesium atoms, respectively. We evaluated the frequency stability of the light source using heterodyne measurements between two identical setups. The developed light source can be used to generate frequency-stable photon pairs, a critical requirement for quantum repeaters using Pr:YSO quantum memories.

DOI
10.1364/ao.560656

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We developed a frequency-stable laser light source operating at 436 nm to produce entangled photon pairs at 606 nm and 1.5 µm via spontaneous parametric down conversion. This light source was produced via the sum frequency generation of two lasers operating at 852 and 895 nm, each stabilized to the D2 and D1 transitions of cesium atoms, respectively. We evaluated the frequency stability of the light source using heterodyne measurements between two identical setups. The developed light source can be used to generate frequency-stable photon pairs, a critical requirement for quantum repeaters using Pr:YSO quantum memories.
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We present the development and operation of a tunable, frequency-stabilized, narrow-bandwidth source of entangled photon pairs, which can be tuned to the two D–P transitions in Ca+ ions at 850 and 854 nm. The source is based on spontaneous parametric down-conversion in periodically poled KTiOPO4 (PPKTP) followed by tunable optical filters. Its output bandwidth of 22 MHz coincides with the absorption bandwidth of the calcium ions. Its spectral power density is 1.0 generated pairs (s MHz mW)−1. Here, we report details of the setup which was first described in Haase et al (2009 Opt. Lett. 34 55).
Abstract We demonstrate an ultrabright, narrow-band and frequency-tunable photon-pair source based on cavity-enhanced spontaneous parametric down conversion (SPDC) which is compatible with atomic transition of rubidium D 2 -line (780 nm) or cesium D 2 -line (852 nm). With the pump beam alternating between a high and a low power phase, the output is switching between the optical parametric oscillator (OPO) and photon-pair generation mode. We utilize the OPO output light to lock the cavity length to maintain the double resonances of signal and idler, as well as to lock the signal frequency to cesium atomic transition. With a type-II phase matching and a double-passed pump scheme such that the cluster frequency spacing is larger than the SPDC bandwidth, the photon-pair output is in a nearly single-mode operation as confirmed by a scanning Fabry–Perot interferometer with its output detected by a photomultiplier. The achieved generation and detection rates are 7.24 × 10 5 and 6142 s −1 mW −1 , respectively. The correlation time of the photon pair is 21.6(2.2) ns, corresponding to a bandwidth of 2 π × 6.6(6) MHz. The spectral brightness is 1.06 × 10 5 s −1 mW −1 MHz −1 . This is a relatively high value under a single-mode operation with the cavity-SPDC scheme. The generated single photons can be readily used in experiments related to atomic quantum memories.
We present an experimental setup for generation of entangled-photon pairs via spontaneous parametric down-conversion, based on the femtosecond-pulsed laser. Our entangled-photon source utilizes a 76-MHz-repetition-rate, 100-fs-pulsewidth, mode-locked, ultrafast femtosecond laser, which can produce, on average, more photon pairs than a cw laser of an equal pump power. The output infrared pump photons (λ = 810 nm) are first up-converted to blue light (λ = 405 nm) and, subsequently, down-converted in a 1.5-mm-thick, type-II BBO crystal via spontaneous down-conversion. The resulting entangled pairs are counted by a pair of high-quantum-efficiency, single-photon, silicon avalanche photodiodes. The total down-conversion efficiency of our system, corresponding criterion of the pump power for real entangled coincident events, has been calculated to be 0.86 × 10-9. Our apparatus is intended as an efficient source/receiver system for the quantum communications and quantum cryptography applications.