Quantum dots 'may make unbreakable message exchange possible'

London, August 4 (ANI): Researchers have improved a method to make secure codes called quantum key distribution (QKD) by using the smallest possible packets of light.

The approach's security exploits the fact that quantum systems, once observed, are irrevocably changed.

Previous work using light beams of many photons has suffered reduced security, as some light could be intercepted.

The new work by German researchers solves this issue by using electricity to generate single photons.

That brings closer the prospect of global-scale, functionally uncrackable code distribution.

QKD is not a means of creating codes, or ciphers, but rather a way to share them securely.

With the decoding instructions safe from eavesdroppers, an encoded message - containing far more information than the key itself - can then be shared publicly through simpler means.

A great deal of work has gone into QKD in recent years, and a number of companies even offer off-the-shelf systems that promise quantum security - providing you can install a fibre-optic link between the sender and receiver.

It has even spawned a group of quantum hackers at the Norwegian University of Science and Technology, dedicated to finding ways to beat such systems.

"Quantum dots come in semiconductors, and of course semiconductors are at the heart of all the technology we use," the BBC quoted quoted Sven Hoefling from the University of Wuerzburg as saying.

In 2007, the Swiss government even secured its election results with QKD technology.

But to exploit the fullest security allowed by the peculiar rules of quantum mechanics, each "bit" of information in the key should be en coded onto exactly one photon, sent through air or down a fibre.

Yet it is surprisingly difficult to reliably produce exactly one photon. Many systems that squeeze out tiny amounts of light do so sometimes with one photon, and other times with two or more.

Most often, researchers have used laser sources, filtering down their trillions of output photons in a bid to allow just one to pass.

Each extra photon represents a security risk, as it can be intercepted en route and the receiver would never know.

The solution, according to Sven Hoefling of the University of Wuerzburg, Germany, and colleagues is to use what are called quantum dots to create single photons.

Quantum dots are tiny structures made of semiconductors whose size determines, again through rules set by quantum mechanics, exactly what colour and amount of light they produce - and how often they produce it.

This combination of assured single-photon emission at high rates driven by power no different from a battery, Dr Hoefling said, brings QKD much closer to commercial application.

The team showed that they could generate streams of single photons at rates as high as 95,000 bits per second, passing them through air across a laboratory bench. The team has gone on to pull off the same trick across 500m from one roof to another.

The findings of the study have been published in the New Journal of Physics. (ANI)