Quantum correlations are critical to our understanding of nature, with far-reaching technological [1][2][3][4] and fundamental impact. These often manifest as violations of Bell's inequalities [5][6][7][8], bounds derived from the assumptions of locality and realism, concepts integral to classical physics. Many tests of Bell's inequalities have studied pairs of correlated particles; however, the immense interest in multi-particle quantum correlations is driving the experimental frontier to test systems beyond just pairs. All experimental violations of Bell's inequalities to date require supplementary assumptions, opening the results to one or more loopholes, the closing of which is one of the most important challenges in quantum science. Individual loopholes have been closed in experiments with pairs of particles [9][10][11][12][13][14] and a very recent result closed the detection loophole in a six ion experiment [15]. No experiment thus far has closed the locality loopholes with three or more particles. Here, we distribute three-photon Greenberger-Horne-Zeilinger entangled states[16] using optical fibre and free-space links to independent measurement stations. The measured correlations constitute a test of Mermin's inequality [17] while closing both the locality and related freedom-of-choice loopholes due to our experimental configuration and timing. We measured a Mermin parameter of 2.77 ± 0.08, violating the inequality bound of 2 by over 9 standard deviations, with minimum tolerances for the locality and freedom-of-choice loopholes of 264 ± 28 ns and 304 ± 25 ns, respectively. These results represent a significant advance towards definitive tests of the foundations of quantum mechanics[18] and practical multi-party quantum communications protocols [19].In his breakthrough work, John Bell[5] derived upper bounds on the strength of correlations exhibited by local hidden variable (LHV) theories, very general models of nature in which measurement outcomes in one region of space are independent of the events in other space-like separated regions. Quantum mechanical correlations can violate these bounds. Greenberger, Horne, and Zeilinger (GHZ) extended Bell's argument to the scenario with three-particle entangled states, and showed they could manifest violations of local realism in a fundamentally different way [16,20]. The GHZ argument was converted into the form of an inequality by Mermin[17] which we experimentally tested.An ideal Bell inequality experiment requires separating two or more particles by a large distance and making highefficiency local measurements on those particles using randomly chosen settings and comparing these results [21,22]. The first Bell inequality tests were carried out using twophoton cascades in atomic systems [7,8]. Mermin's inequality was violated using three-photon entanglement from a parametric down-conversion source [23]. However, these and the many other Bell experiments that followed are subject to one or more loopholes that could, in principle, be exploited to yield a violat...

Technological realities limit terrestrial quantum key distribution (QKD) to single-link distances of a few hundred kilometers. One promising avenue for global-scale quantum communication networks is to use low-Earth-orbit satellites. Here we report the first demonstration of QKD from a stationary transmitter to a receiver platform traveling at an angular speed equivalent to a 600 km altitude satellite, located on a moving truck. We overcome the challenges of actively correcting beam pointing, photon polarization and time-of-flight. Our system generates an asymptotic secure key at 40 bits/s. 33. J.-P. Bourgoin, "Experimental and theoretical demonstration of the feasibility of global quantum cryptography using satellites," Ph.D. thesis, University of Waterloo (2014).

Satellite-based quantum terminals are a feasible way to extend the reach of quantum communication protocols such as quantum key distribution (QKD) to the global scale. To that end, prior demonstrations have shown QKD transmissions from airborne platforms to receivers on ground, but none have shown QKD transmissions from ground to a moving aircraft, the latter scenario having simplicity and flexibility advantages for a hypothetical satellite. Here, we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3-10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites. For some passes of the aircraft over the ground station, links were established within 10 s of position data transmission, and with link times of a few minutes and received quantum bit error rates typically ≈3%-5% , we generated secure keys up to 868 kb in length. By successfully generating secure keys over several different pass configurations, we demonstrate the viability of technology that constitutes a quantum receiver satellite payload and provide a blueprint for future satellite missions to build upon.

The NanoQEY (Nano Quantum Encryption) Satellite is a proposed nanosatellite mission concept developed by the Institute for Quantum Computing (IQC) at the University of Waterloo and the Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies (UTIAS) that would demonstrate long-distance quantum key distribution (QKD) between two distant ground stations on Earth using an optical uplink. SFL's existing and proven NEMO (Nanosatellite for Earth Monitoring and Observation) bus forms the baseline spacecraft for NanoQEY, with a QKD receiver payload designed by IQC. The primary objective of the NanoQEY mission would be to successfully distribute at least 10 kbit of secure key between two optical ground stations, where the satellite acts as a trusted node. The secondary mission objective would be to perform Bell tests for entangled photons between ground and space. We designed a compact QKD receiver payload that would be compatible with the mass, volume, power and performance constraints of a low-cost nanosatellite platform. The low-cost rapid schedule "microspace" approach of UTIAS/SFL would allow for the proposed NanoQEY mission to be developed in 2.5 years from project kick-off to launch of the spacecraft, followed by a one-year on-orbit mission.

Abstract. Satellite-based quantum terminals are a feasible way to extend the reach of quantum communication protocols such as quantum key distribution (QKD) to the global scale. To that end, prior demonstrations have shown QKD transmissions from airborne platforms to receivers on ground, but none have shown QKD transmissions from ground to a moving aircraft, the latter scenario having simplicity and flexibility advantages for a hypothetical satellite. Here we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3-10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites. For some passes of the aircraft over the ground station, links were established within 10 s of position data transmission, and with link times of a few minutes and received quantum bit error rates typically ≈3-5 %, we generated secure keys up to 868 kb in length. By successfully generating secure keys over several different pass configurations, we demonstrate the viability of technology that constitutes a quantum receiver satellite payload and provide a blueprint for future satellite missions to build upon.