Entropy Bounds for Device-Independent Quantum Key Distribution with Local Bell Test

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Device-Independent Quantum Key Distribution (DIQKD)

Background:

• Achieving significant Bell violation over long distances is a major challenge in DIQKD due to channel losses and low detection efficiencies.
• Existing methods for certifying nonlocal correlations over extended distances using local Bell tests have limitations in security analysis and key rate bounds.

Purpose of the Study:

• To introduce a general formulation for computing key rates in DIQKD setups that leverage local Bell tests.
• To analyze the security and performance of DIQKD with enhanced long-distance capabilities.

Main Methods:

• Developed a general formulation for key rate computation applicable to DIQKD with auxiliary short-distance devices.
• Integrated this formulation with advanced methods for analyzing standard DIQKD security.
• Evaluated the impact of detection efficiencies on achievable key rates.

Main Results:

• Demonstrated that positive key rates can be achieved in the long-distance branch even with lower detection efficiencies.
• Showed that sufficiently high detection efficiencies in the short-distance devices enable improved DIQKD performance over extended distances.
• The proposed method yields tighter bounds on key rates compared to previous approaches.

Conclusions:

• Leveraging short-distance correlations via local Bell tests offers a promising strategy to enhance the performance of device-independent quantum key distribution over longer distances.
• This approach addresses key limitations in current DIQKD protocols, particularly concerning detection efficiency and security against active attackers.