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Register a new userHigh-birefringence direct UV-written waveguides for heralded single-photon sources at telecommunication wavelengths
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Direct UV-written waveguides are fabricated in silica-on-silicon with birefringence of $(4.9 pm 0.2) times 10^{-4}$, much greater than previously reported in this platform. We show that these waveguides are suitable for the generation of heralded single photons at telecommunication wavelengths by spontaneous four-wave mixing. A pulsed pump field at 1060 nm generates pairs of photons in highly detuned, spectrally uncorrelated modes near 1550 nm and 800 nm. Waveguide-to-fiber coupling efficiencies of 78-91% are achieved for all fields. Waveguide birefringence is controlled through dopant concentration of $mathrm{GeCl_4}$ and $mathrm{BCl_3}$ using the flame hydrolysis deposition process. The technology provides a route towards the scalability of silica-on-silicon integrated components for photonic quantum experiments.
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Single-photon sources based on optical parametric processes have been used extensively for quantum information applications due to their flexibility, room-temperature operation and potential for photonic integration. However, the intrinsically probabilistic nature of these sources is a major limitation for realizing large-scale quantum networks. Active feedforward switching of photons from multiple probabilistic sources is a promising approach that can be used to build a deterministic source. However, previous implementations of this approach that utilize spatial and/or temporal multiplexing suffer from rapidly increasing switching losses when scaled to a large number of modes. Here, we break this limitation via frequency multiplexing in which the switching losses remain fixed irrespective of the number of modes. We use the third-order nonlinear process of Bragg scattering four-wave mixing as an efficient ultra-low noise frequency switch and demonstrate multiplexing of three frequency modes. We achieve a record generation rate of $4.6times10^4$ multiplexed photons per second with an ultra-low $g^{2}(0)$ = 0.07, indicating high single-photon purity. Our scalable, all-fiber multiplexing system has a total loss of just 1.3 dB independent of the number of multiplexed modes, such that the 4.8 dB enhancement from multiplexing three frequency modes markedly overcomes switching loss. Our approach offers a highly promising path to creating a deterministic photon source that can be integrated on a chip-based platform.
The non-deterministic nature of photon sources is a key limitation for single photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon correlated photon pair sources, demonstrating a 62.4% increase in the heralded single photon output without an increase in unwanted multi-pair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two photon interference, required at the core of optical quantum computing and quantum communication protocols.
Single-photon sources (SPSs) are mainly characterized by the minimum value of their second-order coherence function, viz. their $g^{(2)}$ function. A precise measurement of $g^{(2)}$ may, however, require high time-resolution devices, in whose absence, only time-averaged measurements are accessible. These time-averaged measures, standing alone, do not carry sufficient information for proper characterization of SPSs. Here, we develop a theory, corroborated by an experiment, that allows us to scrutinize the coherence properties of heralded SPSs that rely on continuous-wave parametric down-conversion. Our proposed measures and analysis enable proper standardization of such SPSs.
Single photon source represent a fundamental building block for optical implementations of quantum information tasks ranging from basic tests of quantum physics to quantum communication and high-resolution quantum measurement. In this paper we investigate the performance of a multiplexed system based on asymmetric configuration of multiple heralded single photon sources. {To compare the effectiveness of different designs we introduce a single-photon source performance index that is based on the value of single photon probability required to achieve a guaranteed signal to noise ratio.} The performance and scalability comparison with both currently existing multiple-source architectures and faint laser configurations reveals an advantage the proposed scheme offers in realistic scenarios. This analysis also provides insights on the potential of using such architectures for integrated implementation.
We demonstrate a method to monolithically integrate nanowire-based quantum dot single photon sources on-chip using evanescent coupling. By deterministically placing an appropriately tapered III-V nanowire waveguide, containing a single quantum dot, on top of a silicon-based ridge waveguide, the quantum dot emission can be transferred to the ridge waveguide with calculated efficiencies close to 100%. As the evanescent coupling is bidirectional, the source can be optically pumped in both free-space and through the ridge waveguide. The latter onfiguration provides a self-contained, all-fiber, single photon source suitable as a plug-and-play solution for applications requiring bright, on-demand single photons. Using InAsP quantum dots embedded in InP nanowire waveguides, we demonstrate coupling efficiencies to a SiN ridge waveguide of 74% with a single photon purity of 97%.
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