Towards fully passive time-bin quantum key distribution over moving free-space channels

Area of Science:

• Quantum communication
• Quantum cryptography
• Photonics

Background:

• Quantum information encoding in photonic time-bin states faces challenges in free-space communication.
• Phase stabilization and channel turbulence hinder practical applications of distant quantum time-bin interferometers.

Purpose of the Study:

• To demonstrate a novel, reference frame-independent time-bin quantum key distribution (QKD) scheme.
• To overcome limitations of active phase stabilization and multi-mode channels in quantum communication.

Main Methods:

• Developed a passive, self-compensating time-bin quantum communication scheme.
• Utilized hybrid polarization and time-bin entangled photons.
• Avoided active mode filtering, adaptive optics, and active phase alignment.

Main Results:

• Achieved a sustained asymptotic secure key rate > 0.07 bits/coincidence over a 15m multi-mode fiber channel.
• Demonstrated entanglement correlations over a moving 38.5 dB loss free-space channel.
• Showcased a system robust to spatial multi-mode and fluctuating channels.

Conclusions:

• The novel scheme simplifies time-bin encoding for quantum communication.
• This approach is suitable for fluctuating channels and rapidly moving platforms like airborne and satellite systems.
• Enables practical free-space quantum communication without active stabilization or mode filtering.