June 30th, 2015

Signal sent 1700km using photons. The experiment conducted by the University of Padua and the Italian Space Agency opens the way for future hacker-proof telecommunications systems

Sending secure, practically unhackable information a record distance of 1700km using photon bursts "shot" into space and sent back to Earth in a nanosecond, is now possible. The results were achieved by the University of Padua and the ASIspace geodesy facility in Matera, which collaborated to perform the first quantum satellite transmission in history.
The experiment, which is currently being considered for publication by Physical Review Letters, was presented by ASI President Roberto Battiston at the Agency's headquarters together with Paolo Villoresi, leader of the Padua University team that worked on the study, Giuseppe Vallone, the first signature on the article entitled Experimental satellite quantum communications and Giuseppe Bianco, director of the ASI space geodesy facility.
Battiston told the press that "there is international competition to see who can communicate the farthest using a quantum signal," and Italy "has not only beaten the previous record of 144km by a long shot, but did so for the first time ever using a satellite in space".
Today, information travels in bits sent through fibre optics or radio waves. Each bit can be saved, copied or intercepted. Mathematical bits are not therefore suitable for secure communications without an encryption key known by the legitimate correspondents, which can also be cracked.
Quantum communication offers a way to use light as the "messenger", in the form of photons, indivisible micro particles that generate light pulses instead of electric pulses.
Classic bits are replaced by quantum bits - or qubits - used to transfer the quantum state of single photons from a transmitter to a receiver.
Giuseppe Vallone explained that "if information is intercepted during a quantum exchange, the quantum states that make up the message are disturbed, showing the signature of the person listening in". This guarantees an absolute level of protection for data transfer that no other communication system is capable of offering today.
"This experiment, which is the result of 12 years of research" commented Paolo Villoresi, "demonstrated that it is possible to exchange a secure encrypted message via satellite a record-breaking distance and allowed us to confirm some basic principles of quantum mechanics, such as maintaining the state of a photon in a telecommunications channel".
In terms of global use of quantum communications, space is the frontier: "exchanging quantum states between distant correspondents on Earth has some limitations, such as the curve of the Earth's surface, which we can overcome by using satellites", continued Villoresi, while Vallone indicated the International Space Station as the ideal hub for quantum communications.
However, there are no satellites currently in orbit equipped with dedicated quantum transmitters or receivers. In order to conduct the test, the team from the University of Padua turned to the Italian Space Agency's space geodesy facility in Matera. Giuseppe Bianco emphasised how "the centre is the highest performing civilian laser telemetry station in the world, capable of taking distance measurements accurate to one millimetre. This meant that we could direct a photon burst towards a satellite in orbitwith retro-reflectors and record the return signal while it travelled back to Earth at the speed of light".
As well as confirming that the Earth's atmosphere is suitable for transmitting photons, the study shows that satellite quantum communications are possible, creating the possibility of genuinely hacker-proof communications in the near future. The goal, in which Italian research centres are playing their role, is important and highly attractive.
Battiston concluded that "apart from having important economic and scientific applications, the experiment opens a door that the Italian Space Agency intends to keep open, because it is founded on the excellence of our scientists".