High-fidelity spatial mode transmission through a 1-km-long multimode fiber via vectorial time reversal [article]

Yiyu Zhou, Boris Braverman, Alexander Fyffe, Runzhou Zhang, Jiapeng Zhao, Alan E. Willner, Zhimin Shi, Robert W. Boyd
2020 arXiv   pre-print
The large number of spatial modes supported by multimode fiber (MMF) is a promising platform for boosting the secure key rate of quantum key distribution (QKD) by orders of magnitude. However, the practical use of multimode fibers in QKD is severely hampered by modal crosstalk and polarization mixing. Here we show that high mode fidelity can be achieved for a large number of spatial modes propagating through a 1-km-long, standard, graded-index, multimode fiber by using vectorial time reversal.
more » ... ectorial time reversal is accomplished digitally by means of a single-shot measurement for each mode of interest, without the need to probe the entire transfer matrix of the fiber. We characterize the crosstalk for 210 modes, in each of the Laguerre-Gauss and Hermite-Gauss basis sets. Through the use of vectorial time reversal, we show an average mode fidelity above 80% for a fiber without thermal or mechanical stabilization, allowing for a channel capacity of up to 13.8 bits per sifted photon for high-dimensional quantum communication. We also propose a practical and scalable mode-multiplexed QKD protocol that cannot be achieved by alternative methods. Our method can be directly used to increase the channel capacity of QKD by two orders of magnitude.
arXiv:2003.09883v2 fatcat:osxnj4eobvhn5kyoe45uraobxu