High-dimensional decoy-state quantum key distribution over multicore telecommunication fibers

TLDR

Multiplexing augments transmission capacity by combining multiple signals over the same data channel, a strategy successful in classical communications but only limitedly practical in quantum communications due to the need for higher‑dimensional quantum systems; high‑dimensional QC using the transverse momentum of single photons is being pursued, yet no approach has proven fully compatible with existing telecommunication fibers. The study demonstrates a secure high‑dimensional decoy‑state quantum key distribution session over a 300‑m multicore optical fiber, overcoming previous compatibility challenges. The protocol encodes high‑dimensional quantum states in the transverse core modes of the fiber, with theoretical analysis indicating positive secret key rates over metropolitan distances. The experiment achieved secure key distribution over 300 m of multicore fiber, and theory predicts positive secret key rates over metropolitan distances.

Abstract

Multiplexing is a strategy to augment the transmission capacity of a communication system. It consists of combining multiple signals over the same data channel and it has been very successful in classical communications. However, the use of enhanced channels has only reached limited practicality in quantum communications (QC) as it requires the manipulation of quantum systems of higher dimensions. Considerable effort is being made towards QC using high-dimensional quantum systems encoded into the transverse momentum of single photons, but so far no approach has been proven to be fully compatible with the existing telecommunication fibers. Here we overcome such a challenge and demonstrate a secure high-dimensional decoy-state quantum key distribution session over a 300-m-long multicore optical fiber. The high-dimensional quantum states are defined in terms of the transverse core modes available for the photon transmission over the fiber, and theoretical analyses show that positive secret key rates can be achieved through metropolitan distances.