Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China;
Center for Atomic and Molecular NanoSciences Tsinghua University Beijing 100084 China;
quantum key distribution; free space; linear optics; faint pulses;