Frequency Upconversion Detection Of Single Photons In Communication Wavelength And Quantum Detector Tomography Calibration

Quantum-secure communication based on fiber transmission and satellite transmission has developed rapidly in recent years.Many countries paid close attention to the development of quantum information technology.China has deployed the first long-distance quantum-secure communication line "Beijing-Shanghai trunk line" in the year of 2013,which took the lead in application of quantum information technology and gained a series of valuable experience.With the continuous development of quantum information technology,the single-photon detection technology for the communication band infrared photons,which is the most commonly used carrier for quantum information,has also been pushed forward.However,the current nearinfrared single photon detectors have strict limitations in performance.Single-photon detection based on frequency upconversion bridges between nearinfrared photons and Si-APDs.Si-APDs have high detection efficiency and low dark count in the visible light range working at room temperature,and they are compact and inexpensive.Using Si-APDs to detect converted near-infrared single photons will fully exploit their advantages.It has been proved that single photon frequency upconversion won't destroy the quantum state of the initial single-photon signal,which makes frequency upconversion single-photon detectors can be used in quantum information field.In view of the challenges on detection bandwidth,filtering efficiency and quantum characteristics of near-infrared frequency upconversion single-photon detectors,the following research has been done: The effect of pump bandwidth on converted signal bandwidth was studied.Detection of near-infrared single-photon with a bandwidth of 7.2 nm has been realized.Single-photon upconversion experiment based on type ? phase-matched was carried out.And the effect of polarization filtering applied to upconversion detector was studied.The quantum detector tomography was applied to the near-infrared single-photon frequency upconversion detector for comprehensive quantum characterization.The main research results and innovations of this paper are summarized as follows:1.In order to improve the bandwidth of upconversion detection,a broadband near-infrared single-photon frequency upconversion detection scheme based on broadband pump is proposed and experimentally denonstrated.Firstly,the relationship between signal bandwidth and pump bandwidth in frequency upconversion process was derived theoretically,and it was proved that the bandwidth of the converted signal was proportional to the pump bandwidth under the condition of phase matching.Synchronized signal laser source and pump laser source were build as well as an upconversion system based on PPLN crystal.Infared single photons with spectrum as wide as 7.2 nm was upconvertd applying pump centered at 1.04 ?m with a bandwidth of 10 nm.The conversion efficiency was up to 18.6%,and the bandwidth of SFG was 0.2 nm,corresponding to a bandwidth compression ratio of 36.The deviation caused by the group velocity dispersion was calculated.And the effect of different pump powers on the conversion efficiency and dark count at singlephoton level was also explored.2.In order to improve the filtering efficiency of noise in the upconversion process,a single-photon frequency upconversion experiment based on type ? phase matching with polarization filtering scheme was proposed and experimentally explored.Firstly,the distribution of noise in the upconversion process was analyzed.The polarization state of upconverted SFG and noise based on type ? phase matching was theoretically derived.A single-photon frequency upconversion detector based on type-? phase matching was built,and the detection efficiency was about 0.07% with pump power of 1.85 m W.95.4% of the pump parametric fluorescence noise was filtered by polarization filter,and the transmittance for SFG photons was close to 100%.3.A full quantum detector tomography of an infrared single-photon frequency upconversion detector was presented to investigate whether it has quantum characteristics.A self-built synchronously pumped near-infrared upconversion single-photon detector was used as the representative object.A maximum detection efficiency of 37.6% was achieved at wavelength of 1558 nm with a background noise about 300 counts/s.Using coherent states with different average photon numbers as the probe,the quantum detector tomography was performed,and POVM matrix of the detector was reconstructed based on the quantum tomography data.The Wigner functions of the detector was rebuilt as well,and the quantum feature of the detector was manifested by the presence of negative values of the Wigner functions.