Large-alphabet quantum key distribution using energy-time entangled bipartite States

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Quantum Optics

Background:

• Quantum Key Distribution (QKD) offers secure communication by leveraging quantum mechanics principles.
• Existing QKD protocols often face limitations in key generation rate and alphabet size.
• Energy-time entanglement provides a robust quantum resource for secure communication.

Purpose of the Study:

• To present a novel protocol for large-alphabet quantum key distribution (QKD).
• To utilize energy-time entangled biphotons for enhanced key generation.
• To demonstrate the feasibility and security of the proposed QKD protocol.

Main Methods:

• Employing energy-time entangled biphotons as the quantum resource.
• Utilizing binned, high-resolution timing measurements for key generation.
• Analyzing Franson interference fringe visibility to determine quantum channel security.

Main Results:

• Generation of a large-alphabet key with over 10 bits of information per photon pair.
• Demonstration of QKD with a 5% bit error rate, yielding 4 bits of information per photon pair.
• Confirmation that energy-time entanglement is robust for long-distance fiber transmission.

Conclusions:

• The proposed protocol enables large-alphabet QKD with high information capacity.
• The security of the quantum channel is reliably assessed through interference fringe visibility.
• The protocol's design is readily scalable to even larger alphabets and suitable for practical, long-distance applications.