(Press-News.org) Single particles of light, also known as photons, have been produced and implemented into a quantum key distribution (QKD) link, paving the way for unbreakable communication networks.
The results of the experiment, undertaken by a close collaboration of researchers based in Wuerzburg, Munich and Stuttgart, have been published today, Thursday 2 August, in the Institute of Physics and German Physical Society's New Journal of Physics.
The single photons were produced using two devices made of semiconductor nanostructures that emitted a photon each time they were excited by an electrical pulse. The two devices were made up of different semiconductor materials so they emitted photons with different colours.
QKD is not a new phenomenon and has been in commercial use for several years; one of its first uses was to encode the national election ballot results in Switzerland in 2007. The techniques currently being used on a commercial scale rely on lasers to create the source of photons; however, researchers hope to further increase the efficiency of QKD by returning to the original concept of using single photons for generating a secure key.
One of the project coordinators, Dr Sven Hoefling, said: "The nature of light emitted by lasers is very different from light emitted by single photon sources. Whereas the emission events in lasers occur completely random in time, an ideal single photon source emits exactly one photon upon a trigger event, which in our case is an electrical pulse.
"The random nature of emission events from strongly attenuated lasers sometimes results in the emission of two photons very close to each other. Such multiple photon events can be utilized by an eavesdropper to extract information.
"Single photon sources, such as the ones used in our study, are predestined for use in the secure communication systems using quantum communication protocols."
QKD is a process that enables two parties, 'Alice' and 'Bob', to share a secret key that can then be used to protect data they want to send to each other. The secret key is made up of a stream of photons that 'spin' in different directions – vertically, horizontally or diagonally – according to the sender's preferences.
The laws of physics state that it is not possible to measure the state, or 'spin', of a particle like a photon without altering it, so if 'Eve' attempted to intercept the key that was sent between 'Alice' and 'Bob', it would become instantly noticeable.
In their experiment, the single photons were produced with high efficiency, then made into a key and successfully transmitted from the sender to the receiver across 40 cm of free space in the laboratory.
The researchers are aware that to make this experiment more practical and commercially viable, it needs to be scaled up so that quantum keys can be sent over larger distances. To do this, quantum repeater stations need to be incorporated into the network to 'amplify' the message.
"Meanwhile, quantum keys have been sent over 500 metres of free space on top of the roofs in the centre of Munich, Germany. Several projects have also been funded to develop this technology further," continued Hoefling.
###From Thursday 2 August, this paper can be downloaded from http://iopscience.iop.org/1367-2630/14/8/083001/article
Notes to Editors
Contact
1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Press Officer, Michael Bishop:
Tel: 0117 930 1032
E-mail: Michael.Bishop@iop.org
Quantum key distribution using quantum dot–single photon emitting diodes in the red and near infrared spectral range
2. The published version of the paper "Quantum key distribution using quantum dot–single photon emitting diodes in the red and near infrared spectral range" (Tobias Heindel et al 2012 New J. Phys. 14 083001) will be freely available online from Thursday 2 August. It will be available at http://iopscience.iop.org/1367-2630/14/8/083001/article
3. New Journal of Physics publishes across the whole of physics, encompassing pure, applied, theoretical and experimental research, as well as interdisciplinary topics where physics forms the central theme. All content is permanently free to read and the journal is funded by an article publication charge.
IOP Publishing
4. IOP Publishing provides publications through which leading-edge scientific research is distributed worldwide. IOP Publishing is central to the Institute of Physics (IOP), a not-for-profit society. Any financial surplus earned by IOP Publishing goes to support science through the activities of IOP. Beyond our traditional journals programme, we make high-value scientific information easily accessible through an ever-evolving portfolio of community websites, magazines, conference proceedings and a multitude of electronic services. Focused on making the most of new technologies, we're continually improving our electronic interfaces to make it easier for researchers to find exactly what they need, when they need it, in the format that suits them best. Go to http://ioppublishing.org/
The Institute of Physics
5. The Institute of Physics is a leading scientific society promoting physics and bringing physicists together for the benefit of all.
It has a worldwide membership of around 40 000 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications. Go to www.iop.org
The German Physical Society
6. The German Physical Society (DPG) with a tradition extending back to 1845 is the largest physical society in the world with more than 59,000 members. The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. It supports the sharing of ideas and thoughts within the scientific community, fosters physics teaching and would also like to open a window to physics for all those with a healthy curiosity.
Major step taken towards 'unbreakable' message exchange
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