The quantum properties of light can be used to develop protocols for communication that are entirely immune to eavesdropper attacks. Quantum communication is perhaps the most advanced of the quantum technologies. Our work in this area has extended from engineering studies to fundamental physics studies. Our work in the past year has involved constructing and characterizing an underwater quantum communication channel , which could be of great use in national defense, for example, in communication between a surface ship and a submarine. We also studied the influence of state-dependent diffraction  on the integrity of a transverse-mode-multiplexed quantum communication system. This concern is of special importance for systems that employ a large state space, for which case it is likely that not all states would have the same far-field intensity distribution. We show that this problem can be minimized by pre-compensating each state so that they have the same loss due to diffraction.
- Characterization of an underwater channel for quantum communications in the Ottawa River, F. Hufnagel, A. Sit, F. Grenapin, F. Bouchard, K. Heshami, D. England, Y. Zhang, B. J. Sussman, R. W. Boyd, G. Leuchs, and E. Karimi, Optics Express 27,26346-26354 (2019).
- Performance analysis of d-dimensional quantum cryptography under state-dependent diffraction, J. Zhao, M. Mirhosseini, B. Braverman, Y. Zhou, S. M. H. Rafsanjani, Y. Ren, N. K. Steinhoff, G. A. Tyler, A. E. Willner, and R. W. Boyd, Phys. Rev. A 100, 032319 (2019).