Short Pulse Technology And Its Applications In Quantum Information Experiments

As the combination of the quantum mechanics and classic information science,quantum information based on principles of the quantum mechanics solves the calculation ability and information security,which are difficult to interpret in classic information science,through re-characterization and processing on classic information.Standing as part of quantum information science,quantum network guarantees the absolute safety of communication by replying on principles of quantum mechanics.In this thesis,the single photon detector and short pulse light source in the electronic system of the quantum cryptography communication underlying implementation structure are investigated.The narrowing between avalanche coincidence pulse and gate pulse time width in the gated-mode single photon detector will shrink the the time of avalanche photodiode under the Geiger mode,which shall reduce after pulse and DCR of the single photon detector.In the meantime,increasing repetition frequency of the detector also generates higher requirement for the narrowing of the gate pulse time.In order to cooperate with the quantum key distribution system with higher repetition frequency,the recurrence of frequency of the short pulse light would rise and pulse width reduces.The reduction of the light pulse width will improve the time accuracy of the arrival of photon,laying the foundation of the narrowing of gate signals.Through employing avalanche matching pulse signal and gate pulse signal of the single photon detector optimized by short pulse technology and pulse excitation signal of short pulse light in the quantum key distribution system,the bit error ratio in the system is reduced and communication bit ratio.In the communication protocol of the quantum key distribution system,the amplitude and phase of the light source need modulation.The corresponding modulating signals in the electronic system should meet the requirement of the tunable period and modulation depth.In the thesis,the pulse amplitude modulation code with repetition of 10GHz-lbit,5GHz-2bit and 2.5GHz-bit are achieved through designing a single-period tunable amplitude pattern pulse generator.This pattern pulse applies tunable depth modulation on electro-optic modulator to validate pulse amplitude coding through decoy protocol with single light source.The amplitude and the pulse width are crucial to the performance of the gated mode single photon detector.In this thesis,under the help of short pulse technique,the communication band single photon detection of detecting efficiency of 10.90%and 30MHz repetition frequency is performed via producing gated mode signal with amplitude of 4V and FWHM of 0.77nS.With respect to narrower effective gate width,the very detector achieves lower after pulse probability comparing to similar products but remains a desired detection efficiency.As for single photon detector under free running mode,decreasing the avalanche-quench delay will reduce after-pulse and DCR probability.The thesis develops a fast-speed response structure with 2.11 nSvalanche-quench delay in high speed circuit design,and a quench pulse with amplitude of 14V is generated through short pulse technique.Considering the increasing repetition frequency and high time resolution of the single photon detector,pulse with extremely narrow time width and low time jitter is required as excitation signal for the short pulse light source.In this thesis,we develops a periodic pulse light source with repetition frequency of 4.3GHz through narrow pulse technology,and analyzes the relation between input signal and laser pulse signal under gain switching mode through simulation.In this paper,the innovation points are as follow:(1)The article designs and validates a prototype circuit of the pattern pulse generator with single period and tunable amplitude,achieving modulation of amplitude within single period of code pattern.And a primary amplitude coding of decoy protocol is performed by using the pulse generator.(2)A delay line of air medium with bandwidth of 7.00GHz is designed and used for synchronization of multiple short pulse signals.The delay line also performs continuous modulation on delay within 100pS.(3)The thesis generates a short pulse coincidence gate of high time-resolution and 100ps time width in the gated mode single photon detector,allowing narrowing of the gated mode signal and high precision alignment.The after pulse of the detector is reduced and the precise measurement of effective gate width is conducted.