چكيده به لاتين
Most of quantum key distribution protocols are based on single photon technology. Since these protocols are required single photon sources to send information, it is also necessary to use single-photon detectors to read the information. Single-photon detectors based on superconducting nanowires are the main emerging photon counting technology. These types of detectors, unlike conventional single-photon detectors, show high sensitivity and good performance at near-infrared wavelengths, especially in the 1300nm-1550nm range, which are suitable for quantum information processing.
In this thesis, a complete physical model is presented by examining the theory of photon detection process in a current carrying superconducting nanowire and reviewing and comparing the various theoretical models available for this purpose. In order to improve the important detection parameters considered in the processing of quantum information such as detection efficiency, single-photon counting rate and timing jitter, the principles of single-photon detection performance based on superconducting nanowires as well as their physical structure are examined. The most suitable physical model for these devices is based on the formation of a hotspot, diffusion of quasiparticles, the collapse of the potential barrier of magnetic vortices and the movement of vortices. This model, unlike the basic physical model based on the formation of a hot spot, in energy Below the near-infrared range, the quantum efficiency decreases exponentially. This result is completely consistent with the experimental results obtained.
According to this new model, we show that the greatest reduction in the maximum vortex potential barrier occurs when the largest number of quasiparticles produced by the collision of a photon occurs in an area about the length of the superconducting coherence length across the nanowire length. This increases 1.8 times by taking into account the saturation state of the generated particles. We also compare the three conventional superconducting materials WSi, TaN and NbN used in nanowires. According to this model, we will define a temporal uncertainty based on random vortex tunneling and examine and compare the temperature dependence and physical dimensions of the structure for WSi, TaN and NbN. Then, as a result of the random motion of the vortices, the quantum detection efficiency of these devices is defined based on the probability of a magnetic vortex passing through the vortex potential barrier, and this efficiency is completely dependent on the temperature and energy of the emitted photon.
