Experimental Twin-Field Quantum Key Distribution through Sending or Not Sending

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Optical Communications

Background:

• Channel loss severely limits practical long-distance quantum key distribution (QKD).
• Traditional decoy-state QKD scales linearly with channel loss.
• Twin-field QKD (TF-QKD) offers improved key rates, scaling with the square root of channel transmittance, but requires precise interference of independent lasers.

Purpose of the Study:

• To demonstrate a practical implementation of twin-field quantum key distribution (TF-QKD) over a long-distance optical fiber.
• To overcome the technical challenges of remote, single-photon level interference between independent lasers.
• To achieve secure key rates exceeding theoretical limits for repeaterless QKD.

Main Methods:

• Utilized frequency and time transfer technology to lock wavelengths of two independent lasers.
• Employed additional phase reference light to estimate and compensate for fiber fluctuations.
• Implemented the sending-or-not-sending (SNS) protocol for TF-QKD with a high-rate single-photon detector over 300 km of optical fiber.

Main Results:

• Successfully demonstrated TF-QKD over 300 km of optical fiber with realistic phase drift.
• Achieved a secure key rate of 1.96×10⁻⁶ at 300 km.
• The demonstrated secure key rate surpasses the theoretical repeaterless secret key capacity of 8.64×10⁻⁷.

Conclusions:

• The developed TF-QKD system effectively mitigates channel loss limitations for long-distance secure communication.
• The integration of frequency/time transfer and phase compensation technologies enables robust, long-haul quantum key distribution.
• This work presents a significant advancement towards practical, high-rate, long-distance quantum cryptography.