Matthias Kolb

Continuous-variable quantum key distribution offers a practical way for doing secure key exchange by means of broadband modulators and coherent detectors operating in the telecom band. Recent advances in theory and practice have improved the security and eased the system implementation. These include composable security with a finite number of distributed Gaussian-modulated coherent states and the use of pilot/reference signals and a real local oscillator for sharing the phase reference across the communicating parties. Here we report the first prepare-and-measure continuous-variable quantum key distribution experiment that can produce composable keys in the finite-size regime with security against collective attacks. Through novel improvements in the existing security proofs and a fast, yet low-noise and highly stable system operation, we obtain a secret key rate $>$5 Mbps over a 20 km long fiber channel. Our demonstration verifies the security of practical continuous-variable quantum key distribution when used for encryption or other cryptographic tasks.