Direct and full-scale experimental verifications towards ground–satellite quantum key distribution

Abstract

Quantum key distribution (QKD) 1,2 provides the only intrinsically unconditional secure method for communication based on principle of quantum mechanics. Compared with fiber-based demonstrations 3-5 , free-space links could provide the most appealing solution for much larger distance. Despite of significant efforts 6-13 , so far all realizations rely on stationary sites. Justifications are therefore extremely crucial for applications via a typical Low Earth Orbit Satellite (LEOS). To achieve direct and full-scale verifications, we demonstrate here three independent experiments with a decoy-state QKD system overcoming all the demanding conditions. The system is operated in a moving platform through a turntable, a floating platform through a hot-air balloon, and a huge loss channel, respectively, for substantiating performances under rapid motion, attitude change, vibration, random movement of satellites and in high-loss regime. The experiments cover expanded ranges for all the leading parameters of LEOS. Our results pave the way towards ground-satellite QKD and global quantum communication network.

Quantum networks: where should we be heading?

“…Since then, there have been significant efforts, and free space QKD and quantum teleportation over a long distance of 144 km were demonstrated [38,39]. Recently, free space QKD experiments were extended to airborne-to-ground [40], and a moving platform consisting of a vibrating turntable and a balloon [41]. In these works, the receiver was located at a fixed place, simulating a downlink from satellite to ground.…”

Quantum-enhanced tomography of unitary processes

“…To make this approximation valid, the detection efficiency must not be dependent on the specific coincidence pattern. Therefore, we applied a discard rule with keep probabilities 1, 0.625, 0.536, 0.625, and 1 for the five possible outcomes, (4,0), (3,1), (2,2), (1,3), and (0,4), respectively [47].…”

“…The most widely used method for this purpose is quantum process tomography (QPT)-in which a mathematical description of a quantum process is reconstructed by estimating the probabilities of outcomes for a selection of probe states and measurement settings. For example for quantum technology, QPT is used to characterize multi-qubit processors [1] and quantum communication channels [2]; across quantum physics, QPT of some form is often the first experimental investigation of a new physical process-for example, recent research into coherent transport in biological mechanisms [3]. QPT has been demonstrated in a variety of physical systems, including ion traps [4], nuclear magnetic resonance [5], superconducting circuits [6] and nitrogen-vacancy color centers [7].…”

Air to ground quantum key distribution

“…In this case a single half wave plate is sufficient to reestablish the common reference frame. In [120], an otherwise similar QKD experiment linking to a hot-air balloon is presented which is, however, realized without any polarization compensation. This is possible as the vertical direction is always well defined for the balloon.…”