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Physical Review A

Narrow-band photon pair generation through cavity-enhanced spontaneous parametric down-conversion

Amideddin Mataji‐Kojouri, Marco Liscidini

Published Nov 20, 2023• 10 citations
Publisher

Abstract

Cavity-enhanced spontaneous parametric down-conversion (SPDC) can be used to implement heralded single-photon sources with narrow bandwidth down to tens of megahertz, thus compatible with atom-based quantum memories. In this work, we propose and study the cavities that are either singly resonant at the frequency of only one of the generated photons or doubly resonant at the frequency of one generated photon and for the pump field. We derive analytical expressions for the generation rate and the spectral brightness as a function of the main structure parameters. Our analysis shows that by exploiting counterpropagating SPDC inside a cavity with properly designed distributed Bragg reflectors, pure narrow-band heralded single photons can be generated. In particular, when a pulsed pump illuminates a 1-mm-long singly resonant cavity, the bandwidth of the resonant and the nonresonant photons will be 120 MHz and 5.7 GHz, respectively, with heralded single-photon purity as high as 0.993. Due to its small absorption probability inside the cavity, the heralding efficiency can approach unity if the nonresonant partner is used as a heralded single photon. Finally, we also show that continuous-wave excitation of a 1-cm-long cavity resonant for the pump and copropagating fields can provide photon pairs in a narrow bandwidth of 10 MHz with spectral brightness as high as $2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $({\text{s}\phantom{\rule{4.pt}{0ex}}\text{mW}\phantom{\rule{4.pt}{0ex}}\text{MHz})}^{\ensuremath{-}1}$. This source can efficiently couple with quantum memories and can find applications in quantum information processing and communication.

DOI
10.1103/physreva.108.053714

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Cavity-enhanced spontaneous parametric down-conversion (SPDC) can be used to implement heralded single-photon sources with narrow bandwidth down to tens of megahertz, thus compatible with atom-based quantum memories. In this work, we propose and study the cavities that are either singly resonant at the frequency of only one of the generated photons or doubly resonant at the frequency of one generated photon and for the pump field. We derive analytical expressions for the generation rate and the spectral brightness as a function of the main structure parameters. Our analysis shows that by exploiting counterpropagating SPDC inside a cavity with properly designed distributed Bragg reflectors, pure narrow-band heralded single photons can be generated. In particular, when a pulsed pump illuminates a 1-mm-long singly resonant cavity, the bandwidth of the resonant and the nonresonant photons will be 120 MHz and 5.7 GHz, respectively, with heralded single-photon purity as high as 0.993. Due to its small absorption probability inside the cavity, the heralding efficiency can approach unity if the nonresonant partner is used as a heralded single photon. Finally, we also show that continuous-wave excitation of a 1-cm-long cavity resonant for the pump and copropagating fields can provide photon pairs in a narrow bandwidth of 10 MHz with spectral brightness as high as 2\ifmmode×\else\texttimes\fi1062\ifmmode\times\else\texttimes\fi{}{10}^{6}2\ifmmode×\else\texttimes\fi106 (smWMHz)\ensuremath−1({\text{s}\phantom{\rule{4.pt}{0ex}}\text{mW}\phantom{\rule{4.pt}{0ex}}\text{MHz})}^{\ensuremath{-}1}(smWMHz)\ensuremath−1. This source can efficiently couple with quantum memories and can find applications in quantum information processing and communication.
Efficiently generating photon pairs with high heralding efficiency and high single photon purity that are bandwidth matched to quantum emitters, quantum memories, and other matter-based qubits is critical for quantum networking applications. However, nonlinear optics-based sources require substantial spectral engineering to overcome the orders of magnitude bandwidth mismatch between those sources and qubit systems. A popular solution is cavity-enhanced spontaneous parametric down conversion (SPDC) where the cavity sets the photon bandwidth and simultaneously enhances the spectral brightness of the SPDC. Bulk, free-space configurations are generally required to achieve the MHz-scale bandwidths required to interface with most qubit systems. Replicating these in scalable integrated photonic architectures is an ongoing challenge due to the much higher propagation losses that limit the size and linewidth of chip-based resonators. We show here how an intra-cavity slow light medium, acting as an ultra-narrow filter, would enable narrowband photon pair generation in broadband cavities with high single photon purity and without compromising the heralding efficiency. We show that such metrics can be readily realized in erbium doped thin-film lithium niobate microrings using realistic design parameters.
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.
Abstract In long-distance quantum communication using quantum repeaters with quantum memories, entangled photons at telecommunication wavelengths that can be coupled to quantum memory with high efficiency are required. Typically, entangled photons are generated via spontaneous parametric down conversion (SPDC). However, the phase-matching bandwidth of SPDC is more than 100 GHz, which is much broader than the bandwidth of a Pr 3+ :Y 2 SiO 5 quantum memory (with overall bandwidth of ∼10 GHz while the bandwidth of each frequency channel is ∼10 MHz) suitable for frequency-multiplexed quantum repeaters. In this study, nondegenerate SPDC (1550 nm and 995 nm) inside an optical cavity is used to obtain a narrow linewidth and cluster width of SPDC to match the Pr 3+ :Y 2 SiO 5 bandwidth. We also developed a cavity control mechanism that can fulfill the doubly resonant condition. The developed two-photon source can maximize the coupling efficiency with Pr 3+ :Y 2 SiO 5 by introducing wavelength conversion and is promising for use in a quantum repeater.
Generating single-mode, narrow-band photons with high purity and brightness has proven to be difficult. Researchers at the University of Vienna have designed a photon source using Spontaneous Parametric Down-Conversion (SPDC) with a doubly resonant Optical Parametric Oscillator (OPO) utilizing an additional birefringent crystal to tune clusters independent of SPDC phase-matching. Achieving the doubly resonant condition in the OPO that enables a single mode is the challenge when creating a photon source with both single-mode and narrow-bandwidth. This is resolved here, as the resulting photon source has a bandwidth of 10.9 MHz to match the linewidths of atomic transitions. The source also produces single mode photon pairs at a rate of 47.5 Hz without mode filters reducing loss in the system. This novel design enables research and applications in the quantum realm using hybrid light-matter interactions.
Photonic quantum technologies require efficient sources of pure single photons. We present a heralded single-photon source based on spontaneous parametric down-conversion in a monolithic cavity optimized for high spectral and spatial purity. The source heralds single photons at a wavelength of 1540 nm and a spectral bandwidth of 168 MHz, with a maximum heralding efficiency of 70% including all transmission and detection losses, while keeping the multi-photon contamination below 3%. The cavity enhancement predominantly generates photons into the central cavity mode, with a theoretical upper bound on the spectral purity of 79.4% arising from nonzero overlap with adjacent cavity modes. Spectral isolation of the central cavity mode with an etalon yields an increased measured spectral purity of (96.2 ±\pm± 2.7)%.
Generating single-mode, narrow-band photons with high purity and brightness has proven to be difficult. Researchers at the University of Vienna have designed a photon source using Spontaneous Parametric Down-Conversion (SPDC) with a doubly resonant Optical Parametric Oscillator (OPO) utilizing an additional birefringent crystal to tune clusters independent of SPDC phase-matching. Achieving the doubly resonant condition in the OPO that enables a single mode is the challenge when creating a photon source with both single-mode and narrow-bandwidth. This is resolved here, as the resulting photon source has a bandwidth of 10.9 MHz to match the linewidths of atomic transitions. The source also produces single mode photon pairs at a rate of 47.5 Hz without mode filters reducing loss in the system. This novel design enables research and applications in the quantum realm using hybrid light-matter interactions.