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(a) Normalized photoluminescence spectrum recorded at before spectral filtering under excitation at saturation power. Correlation measurements on the spectrally filtered emission line with (b) excitation pulsed at at low power with APDs gated at , (c) laser excitation at around saturation power ( at this frequency) with detection at , and (d) excitation pulsed at near saturation power with detection at . Counts within of a preceding count in the same detector were rejected to limit the effect of after pulsing. Powers quoted refer to the average power at the input of the microscope.
(Color online) A schematic diagram showing the fiber optic quantum key distribution system. SPS: single-photon source; WDM: wavelength division multiplexer; SF: spectral filter; PC: polarization controller; PBS: polarizing beam splitter/combiner; and FS: fiber stretcher. Standard telecom fibers are used in the link between Alice and Bob.
(Color online) (a) Counts as a function of time on APD1 and APD2 showing a 98.5% visibility before dark count correction and (b) variation in the QBER over the course of a key transfer over of fiber. Each bin represents a sample of 500 sifted bits.
(Color online) Theoretical evaluation comparing the PNS secure transmission distance of our SPS (solid blue curve) with an equivalent WCP system (dashed curve). The solid red curve shows the theoretical sifted bit rate of the SPS. The data points represent our experimental sifted bit rate (square) and secure bit rate (triangle). The inset shows the calculated QBER (line) with the measured value.
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