Practical security of a chip-based continuous-variable quantum-key-distribution system

A chip-based continous-variable quantum-key-distribution (CVQKD) system with a high practical confidentiality performance is crucial for constructing quantum metropolitan communication networks, but imperfections in the chip-based modulation will threaten the practical security of the chip-based CVQKD system. In this paper, we combine the plasma dispersion effect of free carriers to model the carrier fluctuations and reveal the essential mechanism of carrier fluctuations' influence on the system. The simulations show that the chip-based CVQKD system may face potential loophole threats or its performance will dramatically decrease under different carrier fluctuations. Moreover, two preliminary defense strategies are proposed to completely solve the practical security problems commonly induced by modulators in general chip-based CVQKD systems. This work proposes a set of modeling and analysis methods for general chip-based CVQKD systems' modulators, which provides constructive methods to build the chip-based CVQKD system with more rigorous practical security.

Figure 1

Silicon-based electro-optic amplitude modulator based on the Mach-Zehnder interferometer structure.

Figure 2

The difference of total excess noise vs positive carrier fluctions, i.e., real total excess noise of the chip-based CVQKD system (hexagon line) and estimated total excess noise of the chip-based CVQKD system (rhombus line).

Figure 3

The difference of total excess noise vs negative carrier fluctions, i.e., real total excess noise of the chip-based CVQKD system (hexagon line) and estimated total excess noise of the chip-based CVQKD system (rhombus line).

Figure 4

Secret key rate (bits/pulse) vs distance (km) with a carrier fluction ${\delta }_{N_e}=0$ under the asymptotic condition of infinite sampling. The secret key rate estimated by Alice and Bob under a balanced homodyne detector is shown by a solid line. The practical secret key rate under a balanced homodyne detector is shown by a dashed line. The secret key rate estimated by Alice and Bob under a balanced heterodyne detector is shown by a dash-dotted line. The practical secret key rate under a balanced heterodyne detector is shown by a dotted line.

Figure 5

Secret key rate (bits/pulse) vs distance (km) with carrier fluctions (a) ${\delta }_{N_e}=+0.50\%$, (b) ${\delta }_{N_e}=+0.75\%$, (c) ${\delta }_{N_e}=+1.50\%$, and (d) ${\delta }_{N_e}=+1.75\%$ under the asymptotic condition of infinite sampling. The secret key rate estimated by Alice and Bob under a balanced homodyne detector is shown by a solid line. The practical secret key rate under a balanced homodyne detector is shown by a dashed line. The secret key rate estimated by Alice and Bob under a balanced heterodyne detector is shown by a dash-dotted line. The practical secret key rate under a balanced heterodyne detector is shown by a dotted line.

Figure 6

Secret key rate (bits/pulse) vs distance (km) with carrier fluctions (a) ${\delta }_{N_e}=-0.50\%$, (b) ${\delta }_{N_e}=-1.00\%$, and (c) ${\delta }_{N_e}=-1.50\%$ under the asymptotic condition of infinite sampling. The secret key rate estimated by Alice and Bob under a balanced homodyne detector is shown by a solid line. The practical secret key rate under a balanced homodyne detector is shown by a dashed line. The secret key rate estimated by Alice and Bob under a balanced heterodyne detector is shown by a dash-dotted line. The practical secret key rate under a balanced heterodyne detector is shown by a dotted line.