Low-noise single-photon detection is a prerequisite for quantum information processingusing photonic qubits. In particular, detectors that are able to accurately resolve the numberof photons in an incident light pulse will find application in functions such as quantumteleportation and linear optics quantum computing. more generally, such a detector will allowthe advantages of quantum light detection to be extended to stronger optical signals, permittingoptical measurements limited only by fluctuations in the photon number of the source. Herewe demonstrate a practical high-speed device, which allows the signals arising from multiplephoton-induced avalanches to be precisely discriminated. We use a type of silicon avalanchephotodiode in which the lateral electric field profile is strongly modulated in order to realize aspatially multiplexed detector. Clearly discerned multiphoton signals are obtained by applyingsub-nanosecond voltage gates in order to restrict the detector current.
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