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This page was published on 28/06/2007
Published: 28/06/2007


Published: 28 June 2007  
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Security  |  Science in society  |  Space


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Quantum leap in communications

A recent discovery by the European Space Agency (ESA) is set to revolutionise the world of communications through the ingenious application of a quantum phenomenon known as entanglement. While this little known and understood quantum occurrence has been around for a long time, it is only now – thanks to the efforts of European scientists – that steps towards its full exploitation can be achieved.

ESA's Optical Ground Station (OGS) is located at the Observatorio del Teide on Tenerife, and is situated at an altitude of 2393 metres. © ESA
ESA's Optical Ground Station (OGS) is located at the Observatorio del Teide on Tenerife, and is situated at an altitude of 2393 metres.
Quantum mechanics is an exhilarating field of study which, though confusing at times, now has scientists contemplating new secure ways of communicating with satellites. The theory of quantum entanglement is just one part of quantum mechanics whose mystery is slowly being revealed.

An Austro-German-led European team of scientists has provided definitive proof that the quantum effect called 'entanglement' remains intact over a distance of 144 kilometres. This revelation will allow the ESA group to further their efforts towards exploiting the entanglement phenomenon as a way of communicating with satellites with absolute security.

The achievement is no mean feat as even Einstein himself had difficulties completely coming to terms with the phenomenon. Simply put, our world is made up of tiny bits of matter, with even light being made of photons. Light, however, can exist as both a wave and a particle at the same time. This is where the classical laws of physics give way to the laws of quantum mechanics. The complexity of understanding this increases when you consider the fact that our attempts to measure it effectively destroys the supposition of the other existing.

When 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.

In communications, this destructiveness can be effectively applied in quantum cryptography, because any message that is intercepted will be changed through being measured. This behaviour has the potential to allow messages to be swapped with complete confidence. Any eavesdropper listening into the message 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.

This quality makes quantum communications ideal for those, such as the military or in banking, needing the utmost security.

Currently, the ESA team has turned its attention towards taking the experiment into space as it will then be able to test entanglement at distances of over 1 000 kilometres. This will extend the validity of quantum physics theory to macroscopic scales.

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'The revolutions of offshore science', RTDinfo, February 2007

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