Composable free-space continuous-variable quantum key distribution using discrete modulation.

Area of Science:

• Quantum Information Science
• Secure Communication Technologies
• Optical Physics

Background:

• Continuous-variable quantum key distribution (CV-QKD) offers secure communication, nearing classical coherent communication capabilities.
• Discrete modulation in CV-QKD is practical for real-world devices, but experiments typically use asymptotic key rates.
• Expanding CV-QKD beyond fiber optics is crucial for broader network integration.

Purpose of the Study:

• To present a CV-QKD system optimized for atmospheric channels using discrete modulation.
• To demonstrate the feasibility of CV-QKD for non-fiber based secure communication networks.
• To calculate composable finite-size key rates for practical security assessments.

Main Methods:

• Developed a CV-QKD system employing discrete modulation and polarization encoding.
• Utilized the nonbirefringent property of the atmosphere for polarization encoding.
• Implemented a recent security proof to calculate finite-size key rates against collective attacks.

Main Results:

• Successfully demonstrated a CV-QKD system in a laboratory setting with a 3-dB loss channel.
• Calculated composable finite-size key rates, moving beyond the asymptotic regime.
• Integrated a quantum random number generator, error correction, and privacy amplification for key extraction.

Conclusions:

• The developed CV-QKD system is suitable for atmospheric channels, expanding secure communication possibilities.
• Finite-size key rate calculations provide a more realistic security measure for practical CV-QKD deployments.
• Polarization encoding offers a viable strategy for CV-QKD in turbulent atmospheric environments.