Experimental Satellite Quantum Communications

Abstract

Quantum communication (QC), namely, the faithful transmission of generic quantum states, is a key ingredient of quantum information science. Here we demonstrate QC with polarization encoding from space to ground by exploiting satellite corner cube retroreflectors as quantum transmitters in orbit and the Matera Laser Ranging Observatory of the Italian Space Agency in Matera, Italy, as a quantum receiver. The quantum bit error ratio (QBER) has been kept steadily low to a level suitable for several quantum information protocols, as the violation of Bell inequalities or quantum key distribution (QKD). Indeed, by taking data from different satellites, we demonstrate an average value of QBER=4.6% for a total link duration of 85 s. The mean photon number per pulse μ_{sat} leaving the satellites was estimated to be of the order of one. In addition, we propose a fully operational satellite QKD system by exploiting our communication scheme with orbiting retroreflectors equipped with a modulator, a very compact payload. Our scheme paves the way toward the implementation of a QC worldwide network leveraging existing receivers.

Experimental single-photon exchange along a space link of 7000 km

“…The result of the fit for the whole passage of LAGEOS-2 is G t = (4.7 ± 0.2) × 10 8 . Excluding the above mentioned period, the total photon transmission time was then 32 min, that greatly extend the link durations previously reported [20][21][22], that were at the level of few tens of seconds per satellite passage. This is due to two reasons: the duration of line-of-sight with MEO satellites is longer with respect to LEO, and the pointing accuracy is increased, due to the lower angular velocity of the satellite, and lower influence of gravitational perturbation of the Earth crust.…”

“…We tested the synchronization method with two satellites in different orbits: Ajisai, a LEO satellite with altitude of 1490 km also used in [20,22], and LAGEOS-2, a MEO satellite with altitude of 5620 km. For both satellites, we evaluated the difference of the measured time-tags of a complete passage with the nearest t ref calculated by the ancillary SLR pulses.…”

“…To overcome these limitations, in the last decade the feasibility of a quantum channel from an orbiting terminal has been explored both theoretically [14][15][16][17][18][19] and experimentally by exploiting the Ajisai [20] and Champ [21] satellites. Notably, recent transmission of qubits beyond Earth atmosphere [22] proved the feasibility of QC from several low Earth orbit (LEO) satellites, within 1500 km of altitude with respect to Earth surface and with typical passage duration of a few minutes. However, proposals for fundamental tests of Quantum Mechanics with moving frames, involving Special and General Relativity are based on link distances exceeding the LEO scale [23,24].…”

Influence of relativistic effects on satellite-based clock synchronization

“…The feasibility of photon exchanges between a satellite and a ground station has been experimentally demonstrated [21] by the Matera Laser Ranging Observatory (MLRO) in Italy. Most recently, they have reported the operation of experimental satellite quantum communications [22] by sending selected satellites laser pulses. Our scheme can also be generalized to the quantum clock network cases [6,34].…”

“…On one hand several satellite-based quantum optics experiences [18] are feasible with current technology, such as satellite quantum communication [19][20][21][22][23][24][25][26][27], and quantum tagging [28], as well as gravity probes using beam interferometers [29,30] and atomic clocks [31,32] to test the principle of equivalence. Among these experiments, the synchronization of clocks between a satellite and a ground station [33] is an essential step.…”