The experiment allows ESA to take a step closer to exploiting entanglement as a way of communicating with satellites with total security.
Quantum entanglement is one of the many non-intuitive features of quantum mechanics. If two photons of light are allowed to properly interact with one another, they can become entangled. One can even directly create pairs of entangled photons using a non-linear process called SPDC (Spontaneous Parametric Down Conversion).
Those two entangled photons can then be separated but as soon as one of them interacts with a third particle, the other photon of the pair will change its quantum state instantaneously. This happens according to the random outcome of the interaction, even though this photon never did interact with a third particle.
Such behaviour has the potential to allow messages to be swapped with complete confidence. This is because, if an eavesdropper listens into the message, the act of detecting the photons will change the entangled partner. These changes would be obvious to the legitimate receiving station and the presence of the eavesdropper would be instantly detected.
A quantum communications system would be a valuable way to transmit banking information, or military communications, or even to distribute feature films without the fear of piracy.
Even though entanglement has been known about for decades, no one has known whether the entanglement decays over long distance. For example, would a beam of entangled photons remain entangled if it passed through the atmosphere of the Earth? On their journey, the photons could interact with atoms and molecules in the air. Would this destroy the entanglement?
If so, entanglement would be useless as a means of communicating with satellites in orbit, because all signals would have to pass through the Earth's atmosphere. Now, an Austrian-German led team have proved conclusively that photons remain entangled over a distance of 144 kilometres through the atmosphere. That means that entangled signal will survive the journey from the surface of the Earth into space, and vice versa.
In September 2005, the European team aimed ESA's one-metre telescope on the Canary Island of Tenerife toward the Roque de los Muchachos Observatory on the neighbouring island of La Palma, 144 kilometres away. On La Palma, a specially built quantum optical terminal generated entangled photon pairs, using the SPDC process, and then sent one photon towards Tenerife, whilst keeping the other for comparison.
Upon comparing the results from Tenerife with those from La Palma, it was obvious that the photons had remained entangled. "We were sending the single-photon beam on a 144 kilometres path through the atmosphere, so this horizontal quantum link can be considered a 'worst case scenario' for a space to ground link," says Josep Perdigues, ESA's Study Manager.
Additional tests with a quantum communication source that generated faint laser pulses instead of entangled photon pairs were performed in 2006. Faint laser pulse sources emulate single photon sources by attenuating the optical power of a standard laser down to single photon regime. Attenuated lasers are technologically much simpler than entangled photon sources or 'true' single photon sources.
The price you have to pay is the unwanted opportunity for information leakage, due to the non-zero probability of having more than one photon per pulse. In practice, this limits the maximum link distance for exchanging securely a key. By implementing a decoy-state protocol in the experiments using a faint laser pulse source, the maximum link distance (yet secure against an eavesdropper’s action) was extended to values representative of a space to ground experiment.
The team are now studying ways to take the experiment into space. "Being in space will mean that we can test entanglement over lines of sight longer than 1 000 kilometres, unfeasible on Earth, thereby extending the validity of Quantum Physics theory to macroscopic scales," says Perdigues. One option is to use the external pallet on the Columbus module of the International Space Station. Another would be to put the quantum optical terminal on a dedicated satellite of its own. The quantum optical terminal is about 100 kg in mass and fits into a one-cubic-metre box.
Andres Galvez | alfa
Fraunhofer FIT joins Facebook's Telecom Infra Project
25.10.2016 | Fraunhofer-Institut für Angewandte Informationstechnik FIT
Stanford researchers create new special-purpose computer that may someday save us billions
21.10.2016 | Stanford University
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
25.10.2016 | Earth Sciences
25.10.2016 | Power and Electrical Engineering
25.10.2016 | Process Engineering