Heralded single photons (HSPs) and entangled photon pairs (EPPs) via spontaneous parametric down-conversion are essential tools for the development of photonic quantum information technologies. In this paper, we report a novel ultra-high-rate nonclassical light source realized by developing 50 GHz-repetition-rate mode-locked pump pulses and multiplexed superconducting nanowire single-photon detectors. The presence of the single-photon state in the heralded photons with our setup was indicated by the second-order intensity correlation below 1/2 at the heralding rate over 20 Mcps. Even at the rate beyond 50 Mcps, the nonclassicality was still observed with the intensity correlation below unity. Moreover, our setup is also applicable to the polarization-EPP experiment, where we obtained the maximum coincidence rate of 1.6 Mcps with the fidelity of 0.881 ± (0.254 × 10−3) to the maximally entangled state. Our versatile source could be a promising tool to explore various large-scale quantum-photonic experiments with low success probability and heavy attenuation.
Heralded single photons (HSPs) and entangled photon pairs (EPPs) via spontaneous parametric down-conversion are essential tools for the development of photonic quantum information technologies. In this paper, we report a novel ultra-high-rate nonclassical light source realized by developing 50 GHz-repetition-rate mode-locked pump pulses and multiplexed superconducting nanowire single-photon detectors. The presence of the single-photon state in the heralded photons with our setup was indicated by the second-order intensity correlation below 1/2 at the heralding rate over 20 Mcps. Even at the rate beyond 50 Mcps, the nonclassicality was still observed with the intensity correlation below unity. Moreover, our setup is also applicable to the polarization-EPP experiment, where we obtained the maximum coincidence rate of 1.6 Mcps with the fidelity of 0.881 ± (0.254 × 10−3) to the maximally entangled state. Our versatile source could be a promising tool to explore various large-scale quantum-photonic experiments with low success probability and heavy attenuation.
The high-rate detection of entangled photons is essential for advancing photonic quantum information processing. Although several experimental demonstrations have been reported, the achievable coincidence rates have so far remained limited. One of the main bottlenecks arises from the dead time of single-photon detectors, which constrains coincidence detection at high photon-pair generation rates. In this work, we employ 16-pixel superconducting nanowire single-photon detectors (SNSPDs) to mitigate the impact of detector dead time. Consequently, we achieve coincidence rates exceeding 3 million counts per second (Mcps) in two-photon interference and CHSH inequality experiments using a 5-GHz clocked sequential time-bin entangled photon pair source. To the best of our knowledge, this is the first demonstration of multi-Mcps coincidence detection of entangled photons, paving the way for high-speed entangled-photon-based quantum information processing.
Deterministic generation of single photons is essential for many quantum information technologies. A bulk optical nonlinearity emitting a photon pair, where the measurement of one of the photons heralds the presence of the other, is commonly used with the caveat that the single-photon emission rate is constrained due to a trade-off between multiphoton events and pair emission rate. Using an efficient and low noise photon-number-resolving superconducting nanowire detector we herald, in real time, a single photon at telecommunication wavelength. We perform a second-order photon correlation g2(0) measurement of the signal mode conditioned on the measured photon number of the idler mode for various pump powers and demonstrate an improvement of a heralded single-photon source. We develop an analytical model using a phase-space formalism that encompasses all multiphoton effects and relevant imperfections, such as loss and multiple Schmidt modes. We perform a maximum-likelihood fit to test the agreement of the model to the data and extract the best-fit mean photon number $\ensuremath{\mu}$ of the pair source for each pump power. A maximum reduction of $0.118\ifmmode\pm\else\textpm\fi{}0.012$ in the photon g2(0) correlation function at $\ensuremath{\mu}=0.327\ifmmode\pm\else\textpm\fi{}0.007$ is obtained, indicating a strong suppression of multiphoton emissions. For a fixed ${g}^{2}(0)=7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, we increase the single pair generation probability by 25%. Our experiment, built using fiber-coupled and off-the-shelf components, delineates a path to engineering ideal sources of single photons.
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.
Two important challenges in quantum photonics are to generate useful states with high fidelity, and to detect them and verify their properties. Particularly valuable states are single photons and entangled photon pairs in well-defined optical modes, as they can be used in many quantum information protocols or used to build up more complex states. For sources, we employ integrated nonlinear optics (waveguides in lithium niobite and potassium titanyl phosphate) to maximize brightness and go beyond what is possible in bulk optics, showing simultaneously high state fidelity, heralding efficiency, and spectral purity across three experiments: first we show record heralding efficiency in a fully-fibered heralded single-photon source, and use it to probe the tradeoff between spectral purity and heralding efficiency in non-engineered sources. With an engineered source, we then herald up to 50 photons in a nonclassical state. The last source is for polarization-entangled photon pairs, with brightness of 3.5 million pairs/s·mW, fidelity to a Bell state of 96%, heralding efficiency of 43%, and HOM interference visibility of 82%. Once a complex state is constructed, it must also be verified. For this we employ a time-multiplexed detector consisting of a fibre loop and a single-photon detector. Surprisingly, we are able to extract information even in the saturation regime of the detector. We use the click statistics of the time-multiplexed detector to verify the non-classicality of quantum light, and we use its extremely high dynamic range (123 dB) to measure a macroscopic power level with a single-photon detector. Eliminating calibrated attenuators with this approach will allow direct standardization of quantum and classical optical power levels.
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.
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 the best measured value reported to date for heralding rates in the MHz regime. These prime performances, associated with a device-like configuration, are key ingredients for both fast and secure quantum communication protocols.