We present a quantum key distribution system with a 2.5 GHz repetition rate using a threestate time-bin protocol combined with a one-decoy approach. Taking advantage of superconducting single-photon detectors optimized for quantum key distribution and ultra low-loss fiber, we can distribute secret keys at a maximum distance of 421 km and obtain secret key rates of 6.5 bps over 405 km.

One of the main challenges for future quantum information technologies is miniaturization and integration of high performance components in a single chip. In this context, electrically driven sources of non-classical states of light have a clear advantage over optically driven ones. Here we demonstrate the first electrically driven semiconductor source of photon pairs working at room temperature and telecom wavelength. The device is based on type-II intracavity Spontaneous Parametric Down-Conversion in an AlGaAs laser diode and generates pairs at 1.57 µm. Time-correlation measurements of the emitted pairs give an internal generation efficiency of 7 × 10 −11 pairs/injected electron. The capability of our platform to support generation, manipulation and detection of photons opens the way to the demonstration of massively parallel systems for complex quantum operations.PACS numbers: 42.65. Lm, 03.67.Bg, 42.55.Px, Photons have a peculiar advantage in the development of quantum information technologies [1-3], since they behave naturally as flying qubits presenting a high speed transmission over long distances and being almost immune to decoherence [4,5]. The intrinsic scalability and reliability of integrated photonic circuits has recently given rise to a new generation of devices for quantum communication, computation and metrology [6]. Nevertheless even if great progress have been made in the manipulation [7,8] and detection [9] of nonclassical state of light on chip, a complete integration of the light source in the photonic circuitry stays one of the main challenges on the way towards large scale applications; such devices would have a clear advantage over optically driven ones in terms of portability, energy consumption and integration. Semiconductor materials are ideal to achieve extremely compact and massively parallel devices: concerning photon-pair sources, the bi-exciton cascade of a quantum dot has been used to demonstrate an entangledlight-emitting diode at a wavelength of 890 nm [10]. However, even if the use of a single emitter guarantees a deterministic emission, these devices operate at cryogenic temperature, greatly limiting their potential for applications.Optical parametric conversion offers an alternative approach. Despite its non-deterministic nature, this process is the most widely used to produce photon pairs for quantum information and communications protocols. Up to now, entangled photon pairs have been generated by optical pumping in passive semiconductor waveguides by exploiting four-wave mixing in Silicon [11] or SPDC in Aluminium Gallium Arsenide (AlGaAs) [12,13]. Thanks to its direct band gap, the latter platform presents an evident interest for the electrical injection. In order to deal with the isotropic structure of this crystal, several solutions have been proposed to achieve nonlinear optical conversion in AlGaAs waveguides [14][15][16][17][18]; among these, modal phase matching, in which the phase velocity mismatch is compensated by multimode waveguide dispersion, is one of the mos...