Few-Mode-Fiber Technology Fine-tunes Losses in Quantum Communication Systems

Abstract

A natural choice for quantum communication is to use the relative phase between two paths of a single-photon for information encoding. This method was nevertheless quickly identified as impractical for fibre-based communication due to the requirement of a long stabilised interferometer to connect the communicating parties. A modification based on single-photon time-bins has then become widely adopted, with its practicability relying on trading the long interferometer for two shorter local ones. It however, introduces a fundamental loss, which increases with the dimension and that limits its application over long distances. Here, we are able to solve this long-standing hurdle by employing a few-mode fibre space-division multiplexing platform working with orbital angular momentum modes. In our scheme, we maintain the practicability provided by two short interferometers, while the quantum states are transmitted through a few-mode fibre in a configuration that does not require temporal post-selection, thus enabling a detection system without irreversible losses. Our solution can be instantly deployed opening up new paths for the already commercial phase-coding quantum communication systems.

Characterization and stability measurement of deployed multicore fibers for quantum applications

“…However, the transmission of high-dimensional quantum states over multicore fibers requires phase stability between the different cores, since the quantum states are encoded in coherent superpositions of the cores of the fiber. In fact, although the improved phase stability of a single multicore fiber, compared to a bundle of single-core fibers, was already demonstrated over 2 km of a 7-core uncoupled fiber (in laboratory environment), the phase stability of longer deployed MCFs was never tested so far [17,19,20]. In this work, we study the phase stability of a 4-core uncoupled multicore fiber with 25.16 km of length, deployed in the city of L'Aquila [4].…”