Asymptotic security of continuous-variable quantum key distribution with a discrete modulation

Understand

We establish a lower bound on the asymptotic secret key rate of continuous-variable quantum key distribution with a discrete modulation of coherent states.

• The bound is valid against collective attacks and is obtained by formulating the problem as a semidefinite program.
• We illustrate our general approach with the quadrature phase-shift keying (QPSK) modulation scheme and show that distances over 100 km are achievable for realistic values of noise.
• We also discuss the application to more complex quadrature amplitude modulations (QAM) schemes.