Fig. 1. Schematic illustration of CV-QKD protocol with partially characterized entangled source between the two users. (a) Prepare-and-measure (PM) scheme for protocol. (b) Equivalent purification scheme for protocol. Hom, homodyne detection; QM, quantum memory.

Fig. 2. Schematic drawing of the experimental setup. Charlie prepares a two-color EPR entangled state and sends one mode (810 nm) to Alice and the other mode (1550 nm) to Bob. The two users randomly measure the amplitude or phase quadrature of the received signal mode with BHDs. PZT, piezoelectric-transducer; AM, amplitude modulator; PM, phase modulator; FM, Faraday mirror; PBS, polarization beam splitter; DBS, dichroic beam splitter; HR, mirror with high reflection; HWP, half-wave plate; PC, polarization controller; EDFA, erbium-doped fiber amplifier; ATT, attenuator; FPS, fiber phase shifter; BS, 50:50 beam splitter.

Fig. 3. Time-sequence diagram of signal modes and measurement base pulses. It shows the relative timing relationship between the signal mode and its corresponding measurement base pulses.

Fig. 4. Key rates for different distances and quantum correlation of the distributed EPR states. (a) Security key rates versus transmission distance from Charlie to Bob (LB) for different (equivalent) transmission distances from Charlie to Alice (LA) of 0, 1, and 2 km. Solid and dashed lines represent the theoretical simulation with the p base choosing probabilities of P=0.9 and 0.5, respectively. Circles and triangles represent experimental measurement data. (b) Under conditions of LA=2  km and LB=20  km, the quantum correlation between Alice’s and Bob’s amplitude quadrature (1−P=0.1) and phase quadrature (P=0.9).

Fig. 5. Star-type quantum network. The entanglement source is placed at a common network node and is shared by multiple end users.

Fig. 6. Accessible points and key rate in the correlation plane (g,g′) for LA=1  km and LB=20  km. The other parameters are set to β=0.95, εA=0.001, εB=0.01, ηA=0.884, ηB=0.506, νelA=0.02, νelB=0.05, and PA=PB=0.9.

Fig. 7. Zoom of top-left corner of Fig. 6.

Fig. 8. Secret key rate versus transmission distance in the asymptotic case. The simulation parameters are set to β=0.95, εA=0.001, εB=0.01, ηA=0.884, ηs=0.81, ηB=0.506, νelA=0.02, and νelB=0.05.

Fig. 9. Maximum transmission distance from Charlie to Bob (LB) versus the distance from Charlie to Alice (LA).

Fig. 10. Secret key rate versus the transmission distance for three different protocols. The simulation parameters are set to β=0.95, εA=0.001, εB=0.01, ηA=0.884, ηs=0.81, ηB=0.506, νelA=0.02, and νelB=0.05.

Fig. 11. PM and EB schemes of CV-QKD protocol with completely characterized entangled source. Hom, homodyne detection; SQZ, quadrature squeezer; QM, quantum memory.

Fig. 12. Maximum transmission distance from Charlie to Bob (LB) versus the distance from Charlie to Alice (LA) for completely characterized entangled source with two-mode squeezing and antisqueezing of −7.1 and 9.6 dB. The simulation parameters are set to β=0.95, εB=0.01, ηA=0.884, ηB=0.506, νelA=0.02, and νelB=0.05.