| Quantum Key Distribution (QKD) uses quantum mechanical properties of lightfields to establish a secret shared key between two honest parties, named Alice andBob. The theory is based on the laws of quantum mechanics, which haveunconditional security and able to detect eavesdropper. The paper is intended to studytheory and experiment of coherent states QKD base on Stokes parameters, whichprovides a new approach for continuous variable QKD.A new QKD scheme was proposed in this paper, which Alice adopted Gaussianamplitude coding and Stokes polarization coding produced by phase modulation, andBob use homodyne coherent detection Stokes component. A new optical platform wasset up in the system, which allows for co-propagation of signal and LO in one singlebeam. It has advantages of simple structure and high interference. Continuous variableGaussian polarization and magnitude coding were achieved, combined withLabVIEW virtual instrument technology. SU(2) transform box and homodynedetection circuit were designed at the end of this paper.According to quantum mechanics theory, Polarization coding produced by phasemodulation system was built based on LabVIEW. Different kinds of polarizationstates can be generated by changing the input voltage of phase modulator. Thefeasibility of the system was validated by experiments, which show the cosine relationbetween the output voltage of homodyne detection and the input voltage of phasemodulator.The Stokes parameter measurement device was made based ondivision-of-amplitude and homodyne coherent detection, which was proved by Jonesmatrix theory and experiments. The Q-Q-H structure of SU(2) transform box and itscontrol circuit was produced by ATmega16L MCU and LabVIEW. The experimentalresults show that SU(2) transform box is able to randomly select the measure basis ofStokes operators.Experimental implementation bursts ten thousand pulses to form a group; phasemodulator was used to compensate the initial phase of laser. Three bits continuousvariable Gaussian polarization coding was implemented based on LabVIEW, one thousand experiment data were analyzed, and the results show that communicationrate of3kilobits per second, bit error rate of0. Y-axis with equal interval encodingand diode envelope detector hardware decoding was employed, four bits continuousvariable Gaussian amplitude coding was realized based on FPGA embedded system,ten thousand experiment data were analyzed, the results show that communicationrate of4kilobits per second, bit error rate of0.54%.A large magnification (60dB-107dB) and high SNR (>25dB) of the homodynedetection circuit was contrived, which has characteristic of high integration, gainadjustable and eliminate200Hz interference noise. The experimental data indicate thatquantum noise is obedient to the distribution of Poisson, and detection circuit can beused in the coherent state quantum experiments. |
