Wavelength dependence of intrinsic detection efficiency of NbN superconducting nanowire single-photon detector

Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.In this study, we investigate the wavelength dependence of the intrinsic detection efficiency(IDE) for NbN SNSPDs.We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm.Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained.From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted.The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs.Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.

Flux-to-voltage characteristic simulation of superconducting nanowire interference device

Inspired by recent discoveries of the quasi-Josephson effect in shunted nanowire devices,we propose a superconducting nanowire interference device in this study,which is a combination of parallel ultrathin superconducting nanowires and a shunt resistor.A simple model based on the switching effect of nanowires and fluxoid quantization effect is developed to describe the behavior of the device.The current-voltage characteristic and flux-to-voltage conversion curves are simulated and discussed to verify the feasibility.Appropriate parameters of the shunt resistor and inductor are deduced for fabricating the devices.

Superconducting microstrip single-photon detector with system detection efficiency over 90%at 1550 nm

Generally,a superconducting nanowire single-photon detector(SNSPD)is composed of wires with a typical width of∼100 nm.Recent studies have found that superconducting strips with a micrometer-scale width can also detect single photons.Compared with the SNSPD covering the same area,the superconducting microstrip single-photon detector(SMSPD)has smaller kinetic inductance,higher working current,and lower requirements in fabrication accuracy,providing potential applications in the development of ultralarge active area detectors.However,the study of SMSPD is still in its infancy,and the realization of its high-performance and practical use remains an open question.This study demonstrates a NbN SMSPD with a nearly saturated system detection efficiency(SDE)of∼92.2%at a dark count rate of∼200 cps,a polarization sensitivity of∼1.03,and a minimum timing jitter of∼48 ps at the telecom wavelength of 1550 nm when coupled with a single-mode fiber and operated at 0.84 K.Furthermore,the detector’s SDE is over 70%when operated at a 2.1 K closed-cycle cryocooler.