Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

ESA takes steps toward quantum communications

13.06.2007
A team of European scientists has proved within an ESA study that the weird quantum effect called entanglement remains intact over a distance of 144 kilometres.

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
Further information:
http://www.esa.int/SPECIALS/GSP/SEMXM7Q08ZE_0.html

More articles from Information Technology:

nachricht Stable magnetic bit of three atoms
21.09.2017 | Sonderforschungsbereich 668

nachricht Drones can almost see in the dark
20.09.2017 | Universität Zürich

All articles from Information Technology >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>