Quantum key distribution (QKD) is the most mature quantum technology that is available commercially, was realized in numerous protocols, and was even launched into space with dedicated satellites. Yet, the low data-rate per quantum channel and distance-limit are the major bottlenecks of QKD realizations to date. Employing the optical frequency dimension to enhance the data rate of QKD is clearly called for.
We devised, analyzed and realized experimentally a multi-channel version of continuous variable QKD (CV-QKD), where a large multi-bit frame of data can be encoded simultaneously by Alice onto a single source of broadband time-energy entangled photons (by pulse shaping of the bi-photon phase across the spectrum) and then read out by Bob by a simple broadband parametric homodyne measurement. The resulting multi-channel quantum transmitter and receiver are drastically simplified compared to standard schemes, since they require just a single nonlinear medium and a single local oscillator for all the channels (the pump).
The speed-up of our protocol compared to standard protocols is proportional to the number of detectors in the array, which practically can be well over 100 and ideally can reach 10^5 (limited by the ratio of the total bandwidth to the modulation rate of a single channel).
Yaakov Shaked, Yoad Michael, Rafi Vered, Leon Bello, Michael Rosenbluh and Avi Pe’er, “Lifting the Bandwidth limit of Optical Homodyne Measurement with Broadband Parametric Amplification”, Nat. Commun., 9, 609 (2018)