Entanglement-Based Qkd System With Active Phase Tracking

A method entanglement-based quantum key distribution (QKD) that includes active phase tracking and stabilization, comprising:

• forming pairs of reference pulses and pairs of first and second entangled photons all having either the same wavelength or substantially the same wavelength;
• distributing the entangled photons and reference pulses to respective QKD stations Alice and Bob each having respective phase-delay loops with respective adjustable phase-delay elements;
• and
• using the reference pulses to adjust Alice's adjustable phase delay element and/or Bob's adjustable phase-delay element.

A method of entanglement-based quantum key distribution (QKD) having active phase tracking and stabilization, comprising:

• generating coherent pairs of reference photons having a first wavelength;
• generating entangled photons having the first wavelength from coherent pump photons having a second wavelength;
• performing entangled-photon QKD with the entangled photons in an optical system having a plurality of relative phase delays;
• and
• using the reference photons to monitor and maintain the plurality of phase delays.