The combination of single-photon sources, photonic circuits and single-photon detectors enables important functionalities in quantum communications, such as quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. The monolithic integration of quantum photonic components and circuits on a chip is absolutely required to scale implementations of optical quantum information processing to meaningful numbers of qubits (Fig a). The integration of detectors in photonic circuits is particularly challenging, as the complex device structures associated to avalanche photodiodes are not easily compatible with the integration with low-loss waveguides and even less with sources. In 2011, in collaboration with the group of Photonics and Semiconductor Nanophysics at Eindhoven University of Technology, we have demonstrated the integration of SNSPDs on optical waveguides in the GaAs/AlGaAs material system. These waveguide single-photon detectors (WSPDs) present high efficiencies (20% at 1300 nm) with low timing jitter of 60 ps and short deadtime in the ns range.
Up today, the integration of superconducting nanowires is the only practical way for detecting single photons “in situ” in photonic circuits. Fig b) shows a photonic circuit fabricated at IFN, with WSPDS and other passive optical components (i.e., grating couplers, resonators and waveguides) all integrated in a silicon-on-insulator wafer.
References: Sprengers, Gaggero et al. APL 2011, Sahin, Gaggero et al. APL 2013