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Applied Physics Letters

Bright source of indistinguishable photons based on cavity-enhanced parametric down-conversion utilizing the cluster effect

Andreas Ahlrichs, Oliver J. Benson

Published Jan 11, 2016• 28 citations
Publisher

Abstract

We present a bright, simple-to-setup, single-mode source of indistinguishable photon pairs at the cesium D1-line with a bandwidth of about 100 MHz. The source is based on degenerate, cavity enhanced spontaneous parametric down-conversion utilizing the cluster effect. The setup relies on a microcontroller-based digital locking system. A brightness of 1.1×103/(s mW) detected, indistinguishable photon pairs could be measured.

DOI
10.1063/1.4939925

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We present a bright, simple-to-setup, single-mode source of indistinguishable photon pairs at the cesium D1-line with a bandwidth of about 100 MHz. The source is based on degenerate, cavity enhanced spontaneous parametric down-conversion utilizing the cluster effect. The setup relies on a microcontroller-based digital locking system. A brightness of 1.1×103/(s mW) detected, indistinguishable photon pairs could be measured.
We present an efficient and robust source of photons at the 87 Rb D1-line (795 nm) with a narrow bandwidth of δ = 226(1) MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of η heralded = 45(5) % is achieved, and the uncorrected number of detected photon pairs is 3.8 × 10 3 /(s mW). For pair generation rates up to 5 × 10 5 /s, the source emits heralded single photons with a normalized, heralded, second-order correlation function g c ( 2 ) < 0.01 . The source is intrinsically stable due to the monolithic configuration. Frequency drifts are on the order of δ /20 per hour without active feedback on the emission frequency. We achieved fine-tuning of the source frequency within a range of >2 GHz by applying mechanical strain.
Cavity-enhanced spontaneous parametric down-conversion is capable of efficient generation of single photons with suitable spectral properties for interfacing with the atoms. However, beside the remarkable progress of this technique, multimode longitudinal emission remains a major drawback. Here, we demonstrate a bright source of single photons that overcomes this limitation by a novel mode-selection technique based on the introduction of an additional birefringent element to the cavity. This enables us to tune the double resonance condition independent of the phase matching and thus to achieve single-mode operation without mode filters. Our source emits single-frequency-mode photons at 852 nm, which is compatible to the Cs D2 line, with a bandwidth of 10.9 MHz and a detected photon-pair rate of 2.5 kHz at 10 mW of pump power, while maintaining g(2)(0) = 0.13. The efficiency of our source is further underlined by detecting a four-photon rate of 0.28 Hz at 20 mW of pump power. These detected rates correspond to a photon-pair generation rate of 47.5 Hz, and a four-photon generation rate of 37 Hz. Such photon generation rates open up a variety of new applications reaching from hybrid light-matter interactions to optical quantum information tasks based on long temporal coherence.
We demonstrate a high-brightness source of pairs of indistinguishable photons based on a type-II phase-matched doubly-resonant optical parametric oscillator operated far below threshold. The cavityenhanced down-conversion output of a PPKTP crystal is coupled into two single-mode fibers with a mode coupling efficiency of 58%. The high degree of indistinguishability between the photons of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher than 90% without any filtering at an instantaneous coincidence rate of 450,000 pairs/s per mW of pump power per nm of down-conversion bandwidth. For the degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70 pairs/(s mW MHz) is estimated, increasing the spectral brightness for indistinguishable photons by two orders of magnitude compared to similar previous sources.
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.