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Register a new userBright Polarized Single-Photon Source Based on a Linear Dipole
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Semiconductor quantum dots in cavities are promising single-photon sources. Here, we present a path to deterministic operation, by harnessing the intrinsic linear dipole in a neutral quantum dot via phonon-assisted excitation. This enables emission of fully polarized single photons, with a measured degree of linear polarization up to 0.994 $pm$ 0.007, and high population inversion -- 85% as high as resonant excitation. We demonstrate a single-photon source with a polarized first lens brightness of 0.51 $pm $ 0.01, a single-photon purity of 0.939 $pm$ 0.001 and single-photon indistinguishability of 0.915 $pm$ 0.003.
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On-demand indistinguishable single photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fibre networks. Here, we present quantum frequency conversion of near-infrared photons from a bright quantum dot to the telecommunication C-band, allowing integration with existing fibre architectures. We use a custom-built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference frequency generation process. We achieve an end-to-end conversion efficiency of $sim$35%, demonstrate count rates approaching 1 MHz at 1550 nm with $g^{left(2right)}left(0right) = 0.04$, and achieve Hong-Ou-Mandel visibilities of 60%. We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fibre based quantum networking.
A single photon source is realized with a cold atomic ensemble ($^{87}$Rb atoms). In the experiment, single photons, which is initially stored in an atomic quantum memory generated by Raman scattering of a laser pulse, can be emitted deterministically at a time-delay in control. It is shown that production rate of single photons can be enhanced by a feedback circuit considerably while the single-photon quality is conserved. Thus our present single-photon source is well suitable for future large-scale realization of quantum communication and linear optical quantum computation.
We investigate the detection of an ultra-bright single-photon source using highly efficient superconducting nanowire single-photon detectors (SNSPDs) at telecom wavelengths. Both the single-photon source and the detectors are characterized in detail. At a pump power of 100 mW (400 mW), the measured coincidence counts can achieve 400 kcps (1.17 Mcps), which is the highest ever reported at telecom wavelengths to the best of our knowledge. The multi-pair contributions at different pump powers are analyzed in detail. We compare the experimental and theoretical second order coherence functions $g^{(2)}(0)$ and find that the conventional experimentally measured $g^{(2)}(0)$ values are smaller than the theoretically expected ones. We also consider the saturation property of SNSPD and find that SNSPD can be easier to saturate with a thermal state rather than with a coherent state. The experimental data and theoretical analysis should be useful for the future experiments to detect ultra-bright down-conversion sources with high-efficiency detectors.
A BosonSampling device is a quantum machine expected to perform tasks intractable for a classical computer, yet requiring minimal non-classical resources as compared to full-scale quantum computers. Photonic implementations to date employed sources based on inefficient processes that only simulate heralded single-photon statistics when strongly reducing emission probabilities. BosonSampling with only single-photon input has thus never been realised. Here, we report on a BosonSampling device operated with a bright solid-state source of single-photon Fock states with high photon-number purity: the emission from an efficient and deterministic quantum dot-micropillar system is demultiplexed into three partially-indistinguishable single-photons, with a single-photon purity $1{-}g^{(2)}(0)$ of $0.990{pm}0.001$, interfering in a linear optics network. Our demultiplexed source is between one and two orders-of-magnitude more efficient than current heralded multi-photon sources based on spontaneous parametric downconversion, allowing us to complete the BosonSampling experiment faster than previous equivalent implementations.
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.
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