Michael Galili

We characterized intermodal crosstalk in a linearly polarized (LP) mode-multiplexed quantum key distribution (QKD) system based on photonic lanterns. Building on prior QKD demonstrations over few-mode fiber, we performed single-photon-level measurements to evaluate mode isolation and implement automated mode stabilization. Optimized temporal filtering revealed the system’s maximum achievable key rates. Our findings support the practical implementation of QKD multiplexing using LP modes.

Quantum key distribution (QKD) is introduced to make encryption and transmission of data over any public channel unconditionally secure. A key requirement of such a promise is to have access to an encryption key with a similar length as the message and data itself. While QKD has become mature and the key rate significantly increased over the past 20 years, there is still a notable gap between data transmission and key generation rates. High-dimensional QKD is proposed as a method to respond to this demand. Here, we demonstrate a 4-dimensional path-\&-time encoding QKD system with more than 100\% improvement compared to a standard 2D system in the same test-bed, a 52-km deployed multicore fiber link.