A key resource for quantum optics experiments is an on-demand source of single and multiple photon states at telecommunication wavelengths. This letter presents a heralded single photon source based on a hybrid technology approach, combining high efficiency periodically poled lithium niobate waveguides, low-loss laser inscribed circuits, and fast (>1 MHz) fibre coupled electro-optic switches. Hybrid interfacing different platforms is a promising route to exploiting the advantages of existing technology and has permitted the demonstration of the multiplexing of four identical sources of single photons to one output. Since this is an integrated technology, it provides scalability and can immediately leverage any improvements in transmission, detection and photon production efficiencies. Spontaneous parametric downconversion (SPDC) is one of the most commonly exploited methods to generate photons in quantum information science (QIS) applications [1]. However, the spontaneous nature of the process, bounding the probability that N sources each simultaneously create a pair of photons, prevents the demonstration of advanced QIS protocols [2]. Furthermore, the power of the pump laser cannot simply be scaled to increase the pair generation rate since multi-photon events result in noise. Although schemes have been developed which can tolerate multi-photon pairs [3], the majority of protocols have stringent limitations on additional noise [4]. Increasing the repetition rate of the pump laser increases the number of photon pairs generated by a source per second [5], while the probability of generating a photon pair per pulse remains constant. In contrast, active temporal multiplexing schemes can increase the probability of obtaining a photon pair per pulse [6], however due to implementation challenges there has been to date no experimental demonstration. To address this, Migdall et al. proposed a spatial multiplexing scheme to increase photon rates while maintaining the corresponding noise level [7]. This scheme relies on spatially separated heralded sources being actively routed to a single output. A bulk optic demonstration of a multiplexed source used a pair of SPDC crystals [8]. This method suffered from large space and stability requirements and was not scalable beyond a pair of sources. Integrated optics offers a route to miniaturisation, stability and scalability which enabled a number of QIS circuit demonstrations such as a controlled-NOT operation [9], heralded multiphoton entanglement [10] and on-chip quantum relay operation [11]. Here we propose a hybrid photon source which uses SPDC waveguides and laser written components to produce four heralded photons (Fig. 1a). We then use fast fibre-based switches to actively route photons to the desired output (Fig. 1b). Using this architecture we have control over both the photon wavelength and number through temperature tuning and electronically addressed switches.The first demonstration of integrated spatial multiplexing, using a pair of χ (3) silicon photonic crystal (...

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.The reliable generation of single photon states is crucial for a wide variety of quantum optical technologies, ranging from quantum computation and communication [1,2] to quantum metrology and detector calibration [3,4]. As an example, the use of single photon states is essential in quantum key distribution (QKD) protocols, where the unintended presence of more than one photon per time window can be exploited by an eavesdropper to extract part of the information [5].Ideal sources should be able to emit indistinguishable single photons in a deterministic way, at an arbitrarily high repetition rate and with zero probability of multiphoton emissions [1]. In particular, the request of ultrafast photon sources is mandatory to speed up data exchanges in quantum communication protocols. In anticipation to such optimal cases, a pertinent alternative is represented by heralded single photon sources (HSPS), where the detection of one photon of two simultaneously generated is used to herald the emission time of the second one [1,6]. In such schemes, the produced single photons rate is proportional to the detected heralding photon one, R H , and to the heralding efficiency, P 1 , namely, the probability of observing one heralded photon per heralding event. We note that, in experiments, the value of P 1 is essentially determined by optical losses [6].In the original and most common implementations, pairs of simultaneous photons are generated in nonlinear crystals via spontaneous parametric down conversion (SPDC) of a pump beam [6]. In particular, an accurate choice of the phase matching can lead to the production of photons at telecom wavelength, as required for long distance transmission in optical fibers [7,8]. SPDC being a probabilistic process, a way to obtain high photon rates is to increase the probability of generating the photon pairs as well as the photon transmission after the SPDC crystal. Accordingly, in the last years, many papers have been focusing on the realization of bright SPDC sources [9,10] and much effort has been made towards optimizing paired photon collection, separation and prop- * Corresponding author: virginia.dauria@unice.fr agati...

We report an efficient energy-time entangled photon-pair source based on four-wave mixing in a CMOS-compatible silicon photonics ring resonator. Thanks to suitable optimization, the source shows a large spectral brightness of 400 pairs of entangled photons /s/MHz for 500 μW pump power, compatible with standard telecom dense wavelength division multiplexers. We demonstrate high-purity energy-time entanglement, i.e., free of photonic noise, with near perfect raw visibilities (> 98%) between various channel pairs in the telecom C-band. Such a compact source stands as a path towards more complex quantum photonic circuits dedicated to quantum communication systems.