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The idea to detect infrared photons by current-carrying superconducting ultrathin films, mostly of NbN, has led us to interesting new physics. Absorption of a low-energy photon (infrared or visible) by such a film leads to a nonequilibrium state in which superconductivity is locally destroyed. If the film carries a supercurrent (i.e. a current at zero resistance) with a density of up to 107A/cm2 at a liquid He temperature, then a substantial voltage pulse will detected.
In my talk I will discuss the essential features of the working mechanisms offered for such devices in different parts of the electromagnetic spectrum. Superconducting nanowire single-photon detectors (SNSPDs) also show great technological importance. The first application of the NbN SNSPD was debugging silicon CMOS IC devices. The second interesting and important application was quantum cryptography which relies on single-photon communication and enables unconditional security. Besides superior detection performance over a broad optical bandwidth, SNSPDs are also compatible with integrated optical platforms. This is a crucial requirement for applications in emerging quantum-photonic technologies. By embedding SNSPDs in nanophotonic circuits we realize waveguide-integrated single-photon detectors which unite all desirable detector properties in a single device. Besides the application in classical optics, nanophotonic integrated circuits (NPICs) hold promise for a more exotic use. Employing only waveguide-based photonic devices, one can implement on-chip equivalents of free-space optical components, thus offering a new route towards scalable linear optical quantum computing. In this case NPICs are operated with single photons in contrast to the relatively high optical intensities used in classical telecommunication. However, for fully integrated quantum circuits, not only passive devices but also active ingredients such as single-photon sources and integrated single-photon detectors are required. A monolithic implementation of all building blocks of a quantum photonic circuit would then enable to overcome the stability and scalability limitations of bulk optic realizations. With recent advances in the technology of on-chip single-photon sources, all required elements for future quantum photonic networks can be monolithically fabricated with prospect for emerging applications in optical quantum computing.
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