We have tested the experimental prerequisites for a Space-to-Ground quantum communication link between satellites and an optical ground station. The feasibility of our ideas is being tested using the facilities of the ASI Matera Laser Ranging Observatory (MLRO) and existing geodetic satellites such as Lageos 1 and 2. Specific emphasis is put on the necessary technological modifications of the existing infrastructure to achieve single photon reception from an orbiting satellite.
We have tested the experimental prerequisites for a Space-to-Ground quantum communication link between satellites and an optical ground station. The feasibility of our ideas is being tested using the facilities of the ASI Matera Laser Ranging Observatory (MLRO) and existing geodetic satellites such as Lageos 1 and 2. Specific emphasis is put on the necessary technological modifications of the existing infrastructure to achieve single photon reception from an orbiting satellite.
The purpose of this project is to improve the techniques of Quantum Cryptography, to realize a Quantum Key Distribution (QKD) in free space with an orbiting satellite using nowadays technology. With this experiment we characterize the properties of a single photon communication channel from an orbiting satellite in space to a ground based station. We used the facilities of the ASI laser ranging station MLRO (Matera) and the satellite for geodesy Lageos I, equipped with corner-cube retroreflectors, to simulate a single photon transmission from an orbiting satellite.
Extending quantum communication to space environments would enable us to perform fundamental experiments on quantum physics as well as applications of quantum information at planetary and interplanetary scales. Here, we report on the first experimental study of the conditions for the implementation of the single-photon exchange between a satellite and an Earth-based station. We built an experiment that mimics a single photon source on a satellite, exploiting the telescope at the Matera Laser Ranging Observatory of the Italian Space Agency to detect the transmitted photons. Weak laser pulses, emitted by the ground-based station, are directed toward a satellite equipped with cube-corner retroreflectors. These reflect a small portion of the pulse, with an average of less-than-one photon per pulse directed to our receiver, as required for faint-pulse quantum communication. We were able to detect returns from satellite Ajisai, a low-Earth orbit geodetic satellite, whose orbit has a perigee height of 1485 km.
We report on several experiments of single photon transmission from space to ground realized at the Matera Laser Ranging Observatory (MLRO) of the Italian Space Agency in Matera (Italy). We simulated a source of coherent pulses attenuated to the single photon level by exploiting laser ranging satellites equipped with corner-cube retroreflectors (CCRs). By such technique we report QC with qubits encoded in polarization from low-Earth-orbit (LEO) at distance up to 2500km from the ground station, achieving a low quantum bit error ratio (QBER) for different satellites. The same technique is exploited to demonstrate single photon exchange with a medium-Earth-orbit (MEO) satellite, Lageos-2 at more than 7000 km of distance from the MLRO station. In both experiments the temporal jitter of the received counts is of the order of 1.2ns FWHM due to the intrinsic jitter of the single photon detectors. In order to improve the discrimination of signal from the background and reaching distances corresponding to GEO satellites, we improved the detection scheme by using fast single photon detectors with 40 ps FWHM jitter. We report improved single photon detection jitter from Beacon-C and Ajisai, obtaining 340 ps FWHM in the best case.
Satellite quantum communications have rapidly evolved in the past few years, culminating in the proposal, development, and deployment of satellite missions dedicated to quantum key distribution and the realization of fundamental tests of quantum mechanics in space. However, in comparison with the more mature technology based on fiber optics, several challenges are still open, such as the capability of detecting, with high temporal accuracy, single photons coming from orbiting terminals. Satellite laser ranging, commonly used to estimate satellite distance, could also be exploited to overcome this challenge. For example, high repetition rates and a low background noise can be obtained by determining the time-of-flight of faint laser pulses that are retro-reflected by geodynamics satellites and then detected on Earth at the single-photon level. Here we report an experiment with regard to achieving a temporal accuracy of approximately 230 ps in the detection of an optical signal of few photons per pulse reflected by satellites in medium Earth orbit, at a distance exceeding 7500 km, by using commercially available detectors. Lastly, the performance of the Matera Laser Ranging Observatory is evaluated in terms of the detection rate and the signal-to-noise ratio for satellite quantum communications.
Feature Issue on Optical Wireless Communications (OWC) We investigate the design and the accommodation of a quantum communication transceiver in an existing classical optical communication terminal on board a satellite. Operation from a low earth orbit (LEO) platform (e.g., the International Space Station) would allow transmission of single photons and pairs of entangled photons to ground stations and hence permit quantum communication applications such as quantum cryptography on a global scale. Integration of a source generating entangled photon pairs and single-photon detection into existing optical terminal designs is feasible. Even more, major subunits of the classical terminals such as those for pointing, acquisition, and tracking as well as those providing the required electronic, thermal, and structural backbone can be adapted so as to meet the quantum communication terminal needs.
The primary role played by communication in our society gives importance to the problem of securely transmitting sensitive information. Quantum physics can be exploited to solve this problem in a more secure way than it is possible by using classical protocols. The application of quantum physics to communication tasks is the basis of the new quantum communication field, of which quantum cryptography represents the most successful achievement. Quantum communication, however, suffers the presence of losses much more than classical communication. The high level of losses in fiber-based systems, limiting the maximum transmission distance to a few hundred kilometers, makes it necessary to find new ways to go further. A promising solution for extending it to a worldwide scale seems to be the use of satellites. This thesis studies some aspects of quantum communication from an experimental point of view. It presents both the study in the laboratory of quantum communication protocols and the experimental characterization of the satellite-ground channel by using a simulated space source exploiting corner-cube retro-reflectors on geodesic satellites. In addition to this, it also deals with some more technical issues of the problem, such as the construction of a high brilliance polarization-entangled photon source and the improvement of the receiving station for space quantum communication at the Matera Laser Ranging Observatory.