Unconditional security of time-energy entanglement quantum key distribution using dual-basis interferometry

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Quantum Communication

Background:

• High-dimensional quantum key distribution (HDQKD) promises enhanced secure-key rates and photon-information efficiency.
• Time-energy entanglement, generated via spontaneous parametric down-conversion, is a key resource for advanced QKD protocols.

Purpose of the Study:

• To demonstrate the security of HDQKD based on time-energy entanglement against collective attacks.
• To establish a method for quantifying the secure-key rate using visibility data from interferometric measurements.
• To incorporate the decoy-state approach for handling multi-pair emissions in HDQKD.

Main Methods:

• Utilizing Franson and conjugate-Franson interferometers to measure photon-pair frequency and arrival-time correlations.
• Translating continuous-variable quantum key distribution (CV-QKD) Gaussian-state security analysis to the HDQKD protocol.
• Applying the decoy-state approach to account for multiple photon pair emissions.

Main Results:

• The proposed HDQKD protocol is shown to be secure against collective attacks.
• Visibility data from Franson interferometry provides a lower bound for the secure-key rate.
• Over 200 km of optical fiber, a secure-key rate of 700 bit/sec and a photon information efficiency of 2 bits/photon coincidence were achieved with 15% receiver efficiency.

Conclusions:

• Time-energy entanglement HDQKD offers a viable path towards high-speed, high-security quantum communication.
• The security analysis based on visibility measurements provides a practical method for bounding eavesdropping.
• The integration of decoy states and time-energy entanglement enhances the robustness and efficiency of HDQKD systems.