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-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the heralded single-photon output without an increase in unwanted multipair 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.

Photonic chip based time-bin entanglement has attracted significant attention because of its potential for quantum communication and computation. Useful time-bin entanglement systems must be able to generate, manipulate and analyze entangled photons on a photonic chip for stable, scalable and reconfigurable operation. Here we report the first time-bin entanglement photonic chip that integrates time-bin generation, wavelength demultiplexing and entanglement analysis. A two-photon interference fringe with an 88.4% visibility is measured (without subtracting any noise), indicating the high performance of the chip. Our approach, based on a silicon nitride photonic circuit, which combines the low-loss characteristic of silica and tight integration features of silicon, paves the way for scalable real-world quantum information processors.Entanglement is at the heart of photonic quantum technologies such as secure communication [1], super-resolution metrology [2], and powerful computation [3]. Photons are usually entangled in one of three degrees of freedom: polarization, optical path, or time bin. On-chip polarization entangled photon sources have been reported [4,5], but only the components for photon generation were on-chip due to the difficulty of integrating polarization analysis devices. Chip-scale optical path entangled photon generation and analysis [6], and teleportation [7] have seen rapid development, aiming for on-chip quantum computation. Time-bin entanglement is of particular interest because it (i) can be extended to higher dimensions for computation [8]; (ii) is insensitive to polarization fluctuation and polarization dispersion, and therefore very promising for long distance quantum key distribution (QKD) [1]; and (iii) is naturally compatible with integrated optics: photons can be generated in nonlinear waveguides, entangled and analyzed using on-chip unbalanced Mach-Zehnder interferometers (UMZIs) [9,10].For time-bin entanglement to be useful in the real world, the onchip integration of the entire entanglement system is essential. The high performance of the entanglement system not only relies on photon generation, but also hinges on the compactness, scalability and reconfigurability of the photonic circuit that generates the time bins, demultiplex the photons and analyze the entanglement. Refs [9] and [10] reported photon generation from compact silicon devices, but the wavelength demultiplexing was off chip, and entanglement analysis was based on silica waveguides, which have large bending radii due to their low index contrast. These features are incompatible with high density integration.In this paper we report, for the first time, a time-bin entanglement photonic chip that integrates time-bin generation, wavelength demultiplexing and entanglement analysis. Our demonstration was based on a high index contrast silicon nitride (Si3N4) circuit. The waveguide bending radii were reduced from millimeter (for silica) to micrometer scale while maintaining low losses, making high density integration possibl...

We demonstrate low Raman-noise correlated photon-pair generation in a dispersion-engineered 10 mm As2S3 chalcogenide waveguide at room temperature. We show a coincidence-to-accidental ratio (CAR) of 16.8, a 250 times increase compared with previously published results in a chalcogenide waveguide, with a corresponding brightness of 3×10(5) pairs·s(-1)·nm(-1) generated at the chip. Dispersion engineering of our waveguide enables photon passbands to be placed in the low spontaneous Raman scattering (SpRS) window at 7.4 THz detuning from the pump. This Letter shows the potential for As2S3 chalcogenide to be used for nonlinear quantum photonic devices.

Integrated sources of indistinguishable photons have attracted a lot of attention because of their applications in quantum communication and optical quantum computing. Here, we demonstrate an ultra-compact quantum splitter for degenerate single photons based on a monolithic chip incorporating Sagnac loop and a microring resonator with a footprint of 0.011 mm 2 , generating and deterministically splitting indistinguishable photon pairs using time-reversed Hong-Ou-Mandel interference. The ring resonator provides enhanced photon generation rate, and the Sagnac loop ensures the photons travel through equal path lengths and interfere with the correct phase to enable the reversed HOM effect to take place. In the experiment, we observed a HOM dip visibility of 94.5 ± 3.3 %, indicating the photons generated by the degenerate single photon source are in a suitable state for further integration with other components for quantum applications, such as controlled-NOT gates.Integrated photonic circuits have emerged as a promising approach to quantum technologies such as quantum cryptography, which offers provably secure communication [1], and quantum information processing, where for certain computational tasks an exponential speed-up is predicted compared to classical information processing [2,3]. Sources of single photons and entangled pairs of photons are essential to many schemes for long-distance quantum communications and optical quantum computing, and in particular pairs of photons that are degenerate in wavelength and indistinguishable from one another have proven useful in proof-ofprinciple demonstrations of photonic logic gates [4], quantum algorithms [3], entanglement generation [5] and quantum simulations [6]. Degenerate pairs have traditionally been generated using spontaneous parametric down conversion in bulk-nonlinear crystals [7]. However, on-chip photonic circuits with integrated sources of indistinguishable photon pairs are required in order to make this technology scalable.Recently, pair generation has been demonstrated in silicon waveguides using spontaneous four-wave mixing (SFWM), potentially allowing integration of photon sources and circuits with electronic elements [8][9][10]. While non-degenerate photons can be split by wavelength de-multiplexing, this is not possible for degenerate photon pairs, since the two photons share the same properties in all degrees of freedom: spatial, wavelength and polarization [11][12][13]. Splitting these photons probabilistically with a 50:50 directional coupler means they are no longer useful for some tasks; for example a Hong-Ou-Mandel (HOM) dip with probabilistically split photons is limited to a visibility of 50%. An elegant solution is to deterministically split the photons using timereversed HOM interference. So far, this has been demonstrated in fiber Sagnac loops [14,15] and with planar waveguides in a Mach-Zehnder interferometer (MZI) [16,17]. In those schemes, a degenerate pair is created in one of two waveguides which are then combined at a 50:50 coupler in...