Fig. 1. Experimental schematic of transmitted LO PSP-CVQKD scheme. BS1 and BS2, balanced beam splitters; BS3, 99:1 beam splitter; Att, optical attenuator; PBS, polarizing beam splitter; 90° OH, 90° optical hybrid; HD, homodyne detector; Pwr., power meter; T, optical fiber channel transmittance; {xvx, pvx}, vacuum noises from corresponding devices.

Fig. 2. Experimental setup of the high-rate PSP-CVQKD scheme using a thermal source. The red and blue lines represent the polarization-maintaining and single-mode fibers, respectively. ASE, amplified spontaneous emission; EDFA, Er-doped fiber amplifier; BPF, band-pass filter; POL, polarizer; PC, polarization controller; BS, beam splitter; LO, NTK laser source; VOA, variable optical attenuator; Hyb, 90° hybrid; Hom, homodyne detector; Pwr. Meter, power meter; OSC, oscilloscope.

Fig. 3. The excess noise minimum measurement results at attenuation from −20  dB to −40  dB. The blue dots represent the overall excess noise. The orange dots represent excess noise due to passive state preparation ϵpsp. The green dots represent the residual noise except ϵpsp. The red and blue dashed lines are the approximate curves that fit well.

Fig. 4. Experimental excess noise measured with optimal parameter. The lower blue circle points are measured at 5.005 km with 5×105 finite-size blocks. The orange square points represent the excess noise under the worst-case estimator. The red solid line represents the upper bound of the excess noise at 5.005 km. The blue and red dashed lines represent the average experimental excess noise and the average of worst-case excess noise estimator, respectively.

Fig. 5. Experimental key rates and numerical simulations. The blue and purple solid curves depict the simulated secret key rates calculated from the estimated parameters in experiment. The dashed curves show the theoretical secret key rates when considering finite-size effects with different data blocks. The red dotted curve represents the PLOB bound. The green and blue square points correspond to the experimental results at transmission distance of 5.005 km. The lower triangle point, diamond point, and upper triangle point represent the results of Refs. [20,23,24], respectively.

Fig. 6. Histogram of the measurement results and a Gaussian fit curve. Sample size, 4×105.

Fig. 7. Autocorrelation of raw data. Sample size, 4×106.

Fig. 8. The measurement results of thermal source in Alice’s side with both thermal input and vacuum input are shown in phase space.

Fig. 9. Excess noise model for passive state preparation. BS1 and BS2, balanced beam splitter; BS3, 99:1 beam splitter; Att, optical attenuator; HD, homodyne detector; {xvx, pvx}, vacuum noises from corresponding devices.