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Abstract

Systems and methods for performing quantum key distribution (QKD) that allow for an improved signal-to-noise ratio (SNR) when providing active compensation for differences that arise in the system's relative optical paths. The method includes generating at one QKD station (Alice) a train of quantum signals having a first wavelength and interspersing one or more strong control signals having a second wavelength in between the quantum signals. Only the quantum signals are modulated when the quantum and control signals travel over the first optical path at Alice. The quantum and control signals are sent to Bob, where only the quantum signals are modulated as both signal types travel over a second optical path at Bob. The control signals are directed to two different photodetectors by an optical splitter. The proportion of optical power detected by each photodetector represents the optical path difference between the first and second optical paths. This difference is then compensated for via a control signal sent to a path-length-adjusting element in one of the optical paths. The control signals provides a high SNR that allows for commercially viable QKD system that can operate with a high qubit rate and a small qubit error rate (QBER) in the face of real-world sources of noise.

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