High efficiency polarization encoding using a single thermal and electro-optic TFLN-based chip for quantum key...

Area of Science:

• Quantum Information Science
• Integrated Photonics
• Quantum Cryptography

Background:

• Quantum key distribution (QKD) offers unconditional security but faces challenges with polarization encoding stability.
• Discrete optical components in mainstream QKD schemes lead to bulkiness and instability.

Purpose of the Study:

• To develop a compact and stable polarization-encoding chip for QKD.
• To overcome the limitations of conventional silicon-based modulators in QKD systems.

Main Methods:

• Hybrid integration of thin-film lithium niobate (TFLN) and silicon-on-insulator (SOI) technologies.
• Development of a compact architecture with a single thermal and electro-optic phase shifter.
• Dynamic control of four polarization states (|R>, |A>, |L>, |D>) with high extinction ratios (>16.78 dB).

Main Results:

• Demonstration of a polarization-encoding chip enabling dynamic control of four quantum states.
• Achieved a secure key rate (SKR) of 328 kbps and a quantum bit error rate (QBER) of 1.96% at 100 MHz in a 10 km fiber QKD system.
• The TFLN-SOI hybrid design avoids phase saturation and dynamic loss, enhancing stability and scalability compared to silicon-based carrier-depletion modulators (CDMs).

Conclusions:

• The TFLN-SOI hybrid chip represents a significant advancement for stable and scalable polarization-encoded QKD.
• This integrated photonic approach overcomes key limitations, paving the way for practical QKD implementations.
• The chip's performance demonstrates its potential for robust and high-speed quantum communication security.