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APL Quantum

Scalable, tailored purity heralded single-photon source enabled by second harmonic generation of GHz-rate ultrashort pulsed laser

Sangeeta, Bhaskar Kanseri

Published Dec 1, 2025• 3 citations
Publisher

Abstract

We demonstrate a miniaturized, scalable high rate, pulsed single-photon source in the telecom band obtained by heralding a spontaneous parametric downconversion source pumped with a highly tunable GHz repetition rate pulsed laser in an all-guided wave scheme. For developing this source, we first perform second harmonic generation of ultrashort pump pulses varying with GHz rate at the telecom wavelength. Our investigation demonstrates a trade-off between the spectral brightness and the single-photon purity of the heralded single-photon source by controlling the repetition rate of pump pulses. For a 5 GHz repetition rate, a periodically poled lithium niobate waveguide in type-0 configuration produces the highest spectral brightness ∼8.5×106pairs/s/mW/GHz. We quantify the single-photon purity using the second-order autocorrelation function g(2), which reaches the lowest value of ∼(3.4 ± 0.038) × 10−4 for 20 GHz repetition rate pulses, generating heralded single photons at 45 kHz rate. Our all-guided wave configuration offers easy integration and alignment, paving the way for developing scalable, integrable, tunable purity single-photon sources for quantum technology applications, such as quantum communication and quantum networks.

DOI
10.1063/5.0299102

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We demonstrate a miniaturized, scalable high rate, pulsed single-photon source in the telecom band obtained by heralding a spontaneous parametric downconversion source pumped with a highly tunable GHz repetition rate pulsed laser in an all-guided wave scheme. For developing this source, we first perform second harmonic generation of ultrashort pump pulses varying with GHz rate at the telecom wavelength. Our investigation demonstrates a trade-off between the spectral brightness and the single-photon purity of the heralded single-photon source by controlling the repetition rate of pump pulses. For a 5 GHz repetition rate, a periodically poled lithium niobate waveguide in type-0 configuration produces the highest spectral brightness ∼8.5×106pairs/s/mW/GHz. We quantify the single-photon purity using the second-order autocorrelation function g(2), which reaches the lowest value of ∼(3.4 ± 0.038) × 10−4 for 20 GHz repetition rate pulses, generating heralded single photons at 45 kHz rate. Our all-guided wave configuration offers easy integration and alignment, paving the way for developing scalable, integrable, tunable purity single-photon sources for quantum technology applications, such as quantum communication and quantum networks.
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The realization of an ultra-fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state-of-the-art telecom technology, combined with off-the-shelf fiber components and waveguide non-linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single-photon character of the source is inferred by measuring the second-order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi-photon contributions but also represents one of the best measured values reported to date for heralding rates in the MHz regime. These performances, associated with a device-like configuration, are key ingredients for both fast and secure quantum communication protocols.
We report on the realization of a synchronous source of heralded single photons at telecom wavelengths with MHz heralding rates and high heralding efficiency. This source is based on the generation of photon pairs at 810 and 1550 nm via Spontaneous Parametric Down Conversion (SPDC) in a 1 cm periodically poled lithium niobate (PPLN) crystal pumped by a 532 nm pulsed laser. As high rates are fundamental for multi-photon experiments, we show that single telecom photons can be announced at 4.4 MHz rate with 45% heralding efficiency. When we focus only on the optimization of the coupling of the heralded photon, the heralding efficiency can be increased up to 80%. Furthermore, we experimentally observe that group velocity mismatch inside long crystals pumped in a pulsed mode affects the spectrum of the emitted photons and their fibre coupling efficiency. The length of the crystal in this source has been chosen as a trade off between high brightness and high coupling efficiency.
We report on the realization of a synchronous source of heralded single photons at telecom wavelengths with MHz heralding rates and high heralding efficiency. This source is based on the generation of photon pairs at 810 and 1550 nm via Spontaneous Parametric Down Conversion (SPDC) in a 1 cm periodically poled lithium niobate (PPLN) crystal pumped by a 532 nm pulsed laser. As high rates are fundamental for multi-photon experiments, we show that single telecom photons can be announced at 4.4 MHz rate with 45% heralding efficiency. When we focus only on the optimization of the coupling of the heralded photon, the heralding efficiency can be increased up to 80%. Furthermore, we experimentally observe that group velocity mismatch inside long crystals pumped in a pulsed mode affects the spectrum of the emitted photons and their fibre coupling efficiency. The length of the crystal in this source has been chosen as a trade off between high brightness and high coupling efficiency.
Quantum information science (QIS) is a pioneering field of research at the interface of physics and information science. By harnessing the unique properties of quantum mechanics to code, transmit and process information (Qbit), QIS offers significant opportunities to revolutionise information processing and communication strategies. Of the various physical systems currently investigated, single particles of light (photons) are destined to play a central role due to their inherent low noise, ease of manipulation at the single photon level and light-speed transmission. Photonics Qbits can be conveniently generated through the process of spontaneous parametric down-conversion, whereby a photon from a laser beam incident onto a non-linear crystal can spontaneously split into two daughter photons, conserving momentum and energy. Our approach aims at exploiting the high-maturity of both telecom and integrated non-linear optics as enabling technologies. This should lead to the demonstration of ultrafast photon-pair sources, as well as, when one of the photon is used as a trigger, of ultrafastest heralded Fourier transform single photon sources, all in a guided-wave fashion. In this talk, we will present a photon pair source, based on high-brightness periodically poled lithium niobate waveguide, pumped by a state-of-the-art telecom laser operating at a repetition rate of 10 GHz. We will also show how high quality telecommunication components enable the implementation of an ultrafast Fourier transform limited heralded single-photon source complying with the demand of next generation high bit rates quantum networks.
We report a fibre-integrated heralded single-photon source based on a commercial Zn-indiffused MgO:PPLN ridge waveguide operated in Type-0 degenerate spontaneous parametric down-conversion (SPDC). The device emits a broadband spectrum spanning approximately 70 nm across the telecom C-and L-bands, with an absolute brightness of 9.1×1099.1\times 10^{9}9.1×109 pairs/(s mW). After accounting for optical losses, we determine an internal heralding efficiency of 58(5)%. The source maintains high purity, exhibiting a coincidences-to-accidentals ratio exceeding 9×1049\times 10^{4}9×104 and a heralded second-order correlation of gh(2)(0)=(5.53±0.46)×10−4g_{\text{h}}^{(2)}(0) = (5.53 \pm 0.46)\times 10^{-4}gh(2)​(0)=(5.53±0.46)×10−4. Low multi-photon noise and broadband emission demonstrate the viability of such platforms for wavelength-multiplexed quantum networking.