The Utilization of the Galileo Timing Signals for Quantum Communications
Capraro, I.1; Occhipinti, T.2; Zoccarato, P.2; Bonato, C.1; Tamburini, F.3; Barbieri, C.3; Villoresi, P.1
1Department of Information Engineering, University of Padova, and CNR/INFM LUXOR, Padova, Italy; 2Department of Information Engineering and Department of Astronomy, university of Padova; 3Department of Astronomy, University of Padova
Time reference is of critical impact in quantum communication schemes as the temporal filtering is one of the strongest technologies in order to suppress the noise in a quantum channel. This is well demonstrated by one of our past experiment: the study of feasibility of a single-photon transmission from a 1.5m ground telescope (The ASI Matera Laser Ranging station MLRO) to a series of geodetic satellites equipped with retroreflectors (e.g. Ajisai, Lageos) [1]. From this experience we had learnt that a very precise and shared time reference is mandatory in order to discriminate the signal photons from the large unwanted background.
This is true even for ground to ground free space communication especially in daylight transmission. In order to maintain a high cryptographic key production rate, it is necessary to synchronize in a very accurate way the transmitter and the receiver and also to optimize the precision of the start and stop of the transmission along the quantum channel.
Some of the proposed quantum communication schemes use dedicated optical channel for time synchronization while other rely on local oscillator and a posteriori data analysis on known pseudo random sequences [2][3].
We propose to use two Galileo receivers to synchronize the transmitter and receiver clocks of a quantum key distribution system that we are designing.
Galileo receiver will certainly give a very stable time reference, for this reason we think that it is possible to use the pulse per second coming out from it for feeding a phase locked loop circuit on a local oscillator. In this way our system could be put in phase to the Galileo time with an accuracy and precision good enough for the quantum communication purposes.
In this paper we analyze the impact of the Galileo timing performances on the Quantum Key generation rates and present a comparison over other form of synchronization techniques.
In particular Galileo signal will be certified and we are presently studying what kind of improvement this tool will give to quantum communications setups and in this paper we will present also the conclusion of this study.
[1] P. Villoresi, F. Tamburini, M. Aspelmeyer, T. Jennewein, R. Ursin, C. Pernechele, G. Bianco, A. Zeilinger, C. Barbieri “Space-to-ground quantum-communication using an optical ground station: a feasibility study” SPIE proceedings Quantum Communications and Quantum Imaging II conference in Denver, (2004)
[2] J. C. Bienfang et al. “Quantum key distribution with 1.25 Gbps clock synchronization” Optics Express 12, 2011-2016 (2004)
[3] Tobias Schmitt-Manderbach et al. “Experimental Demonstration of Free-Space Decoy-State Quantum Key Distribution over 144 km” PRL 98, 010504 (2007)