Shiji Yang

Direct and full-scale experimental verifications towards ground-satellite quantum key distribution

Full-scale verifications for establishing quantum cryptography communication via satellites are reported. Three independent experiments using a hot-air balloon are performed: on a rapidly moving platform over a distance of 40 km, on a floating platform over a distance of 20 km, and over 96 km in air with a huge loss.

Detection and compensation of basis deviation in satellite-to-ground quantum communications

Basis deviation is the reference-frame deviation between a sender and receiver caused by satellite motion in satellite-to-ground quantum communications. It increases the quantum-bit error ratio of the system and must be compensated for to guarantee reliable quantum communications. We present a new scheme for compensating for basis deviation that employs a BB84 decoding module to detect basis deviation and half-wave plate to provide compensation. Based on this detection scheme, we design a basis-deviation compensation approach and test its feasibility in a voyage experiment. Unlike other polarization-correction schemes, this compensation scheme is simple, convenient, and can be easily implemented in satellite-to-ground quantum communications without increased burden to the satellite.

Real time basis-deviation measurement system based on BB84 module

The purpose of this paper is to present a real time basis-deviation measurement system based on BB84 module. As BB84 module is the essential module in QKD receiver system, the basis-deviation measurement system can be directly implanted into the QKD receiver system to detect the polarization of photon current in real time during quantum key distribution. BB84 module distributes the incident photon current into four photon currents with the polarization of H (Horizontal), V (Vertical), + (+45°) and - (-45°). Their energies can be detected by four APD photon-detectors. Basis-deviation compute equation is deduced with the Stocks-vector of the optical devices path in BB84 module. The energies of the four distributed photon currents are collected in real time and then input to basis-deviation compute equation to calculate the basis-deviation. There is error bears on the effects produced by the optical elements in the BB84 module, so we built a set of software module to foundation the process of the real time polarization measurement system working. Thus we can see how all the parameters of the optical elements effects the calculation results. At last, we built a polarization photon current generator which can produce photon current with continuous changing polarization and a real time basis-deviation measurement system based on BB84 module in laboratory.

Research of Single Photon Detectors Applied in Quantum Communication

Single photon detector (SPD) is one of the key components in quantum communication (QC). To compare the capabilities of SPDs, this paper discussed the current technology of different SPDs and took some experiments. The results show avalanche photodiode (APD) can’t satisfy the development of QC. The count rate of Superconducting nanowire single photon detector (SNSPD) is much higher than APD and the other SPDs, which proves that SNSPD is feasible for high speed QC. And the lower dark count rate of SNSPD makes the lower error rate and the safer communication. Though there are some technical challenges in applications, SNSPD will have broad prospects in QC.

New method for testing diffraction efficiency of AOTF

In view of characteristics of electronically tunable dispersion and staring imaging, imaging spectrometer based on acousto-optic tunable filters (AOTF) has become one of the main technical means of extraterrestrial substance detection all over the world. Diffraction efficiency as one of the main properties of AOTF which is used as a dispersive element in CE-3 Infrared Imaging Spectrometer affects the systems SNR directly. Therefore, it is particularly important to test diffraction efficiency of AOTF. There are some limitations for two testing methods existing which are the use of tungsten halogen lamp with spectrometer and the use of fixed-wavelength laser with power meter. This paper proposes a new method, namely the combination of tunable laser system with energy meters. Nanosecond tunable laser system produces pulsed continuous wavelength tunable laser beams as the testing source, which can support full-band measurement. Besides, beam splitter producing reference beams can reduce the impact of pulsed energy instability. Ratio of diffraction energy and reference energy is considered as the diffraction part while radio frequency (RF) is on. And ratio of direct transmission energy of AOTF and reference energy takes the place of the transmission part while RF is off. The ratio of both is defined as diffraction efficiency. This paper describes the installation based on the new testing method mentioned. Based on the analysis of the test results, it shows that the new testing method is a very practical testing method for diffraction efficiency of AOTF.