Devices for quantum communication over mode-division-multiplexing systems

Abstract

In the absence of quantum repeaters, the only way to increase the quantum communication capacity at a given reach is to employ more modes for encoding and transmitting information. While frequency, temporal, and polarization modes have already been exploited for this purpose, the use of many spatial modes over long distances has only recently become possible owing to the development of low-loss few-mode fibers (FMFs).We will discuss the development of two key enablers of quantum communication over FMF spatial modes: 1) spatiallyentangled photon-pair generator and 2) dynamically-reconfigurable spatial-mode de-multiplexer that can perform projective measurements alternating between two sets of mutually unbiased bases in a given spatial mode space. Both devices are based on the spatial-mode-selective quantum frequency conversion process, implemented in either χ (2) (multimode LiNbO3 waveguide) or χ (3) (custom-made FMF) nonlinear medium.