Abstract
We developed a superconducting nanowire single-photon detection (SNSPD) system based on Gifford-McMahon cryocooler for quantum communication applications. Environmental factors which may influence the system performance are intensively studied. Those factors include temperature fluctuations, the ambient magnetic field and the background radiation. By optimizing the bias circuit, the stability of SNSPD system to electrical noise and disturbance was effectively enhanced, thus making it more suitable for field application. A 4-channel SNSPD system with quantum efficiency higher than 4% at the dark count rate of 10 Hz for λ=1550 nm is integrated and applied into a quantum key distribution (QKD) experiment. QKD was successfully carried out over 100 km optical fiber with the final secure key rate of 1.6 kbps and the quantum bit error rate of less than 2%.
Highlights
Background radiationBlackbody radiation from some parts of the refrigerator with a finite temperature is the main origin of the background radiation
In superconducting nanowire single-photon detection (SNSPD) system, the device is fixed in the oxygen-free copper block which is screwed onto the cold stage
The most important improvement is that our solution significantly improves the stability of SNSPD system without any distortions of the output signal, producing a longterm running SNSPD system for quantum key distribution (QKD) experiment
Summary
Based on GM closed recycled cryocooler, we setup a SNSPD system using the devices made from ultra-thin NbN film. Isolated voltage sources are used to provide a stable bias to SNSPD. The typical bias current Ib is slightly lower than the critical current Ic and supplied through the DC arm of the Bias-Tee which is in series with a 10 k resistor. When the device receives a photon, a transient electrical pulse is generated and output through the RF arm of the Bias-Tee, and amplified by a low noise amplifier. Light is heavily attenuated by a variable attenuator to achieve a photon flux of 1 photon/pulse, adjusted by a polarization controller and arrives the device through a single-mode fiber. By adjusting the polarization of the incident photons, we may obtain the maximal QE of SNSPD
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