Transmission of photonic polarization states through 55-m water: towards air-to-sea quantum communication

Abstract

Quantum communication has been rapidly developed due to its unconditional security and successfully implemented through optical fibers and free-space air in experiment [1][2][3]. To build a complete quantum communication network involving satellites in space and submersibles in ocean, underwater quantum channel has been investigated in both theory and experiment [4][5][6]. However, the question of whether the polarization encoded qubit can survive through a long-distance and high-loss underwater channel, which is considered as the restricted area for satellite-borne radio waves, still remains. Here, we experimentally demonstrate the transmission of blue-green photonic polarization states through 55-meter-long water. We prepare six universal quantum states at single photon level and observe their faithful transmission in a large marine test platform. We obtain the complete information of the channel by quantum process tomography. The distance demonstrated in this work reaches a region allowing potential real applications, representing a step further towards air-to-sea quantum communication.

High‐Dimensional Quantum Communication: Benefits, Progress, and Future Challenges

“…During the last years, the paper was followed by other theoretical investigation [172,173], in which not only point-to-point links were considered, but also non-line of sight underwater communication was studied. Besides, few experimental demonstrations investigated the propagation of polarization-based quantum states [174,175]. However, optical communication in an aquatic environment is subjected to multiple degradation factors: high losses, strong turbulence effects and external noise (sun or moon radiation).…”

Performance analysis of quantum key distribution in underwater turbulence channels

“…The current literature on QKD is mainly limited to the transmissions over fiber optic, atmospheric or satellite links and are not directly applicable to underwater environments with different channel characteristics. There have been only some recent efforts on underwater QKD [16][17][18][19][20][21][22][23][24][25]. For example, in [16] and [17], based on the well-known Beer-Lambert path loss model, the maximum secure communication distance for BB84 protocol in underwater environments was derived to achieve a desired level of quantum bit error rate (QBER) and the secret key rate (SKR).…”

Characterization of an underwater channel for quantum communications in the Ottawa River

“…Underwater quantum communications have been numerically investigated [23] and experimentally demonstrated in laboratory conditions using polarization [24,25], in outdoor conditions using the OAM degree of freedom [26], and over a 55 m water channel using polarization [27] modes [28]. These experimental investigations have lead to several numerical investigations of QKD in underwater channels [29][30][31].…”