Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Breakthrough in Quantum Communication

12.04.2012
A team of scientists at the MPQ realizes a first elementary quantum network based on interfaces between single atoms and photons.

Whether it comes to phoning a friend or to using the internet – our daily communication is based on sophisticated networks, with data being transferred at the speed of light between different nodes.


Figure: Single atoms form the nodes of an elementary quantum network in which quantum information is transmitted via the controlled exchange of single photons. Graphic by Andreas Neuzner, MPQ

It is a tremendous challenge to build corresponding networks for the exchange of quantum information. These quantum networks would differ profoundly from their classical counterparts: Besides giving insights into fundamental questions in physics, they could also have applications in secure communication and the simulation of complex many-body systems, or they could be used for distributed quantum computing. One prerequisite for functional quantum networks are stationary nodes that allow for the reversible exchange of quantum information.

A major breakthrough in this field has now been achieved by scientists in the group of Professor Gerhard Rempe, director at the Max Planck Institute of Quantum Optics and head of the Quantum Dynamics division: The physicists have set up the first, elementary quantum network (Nature, DOI: 10.1038/nature11023, 12 April 2012). It consists of two coupled single-atom nodes that communicate quantum information via the coherent exchange of single photons. “This approach to quantum networking is particularly promising because it provides a clear perspective for scalability”, Professor Rempe points out.

Quantum information is extremely fragile and cannot be cloned. In order to prevent alteration or even the loss of the information, it is necessary to have perfect control over all quantum network components. The smallest stationary memory for quantum information is a single atom, and single photons represent the perfect messengers. Efficient information transfer between an atom and a photon, however, requires strong interaction between the two, which cannot be achieved with atoms in free space. Following a proposal from Professor Ignacio Cirac (director at the MPQ and head of the Theory division), the group of Professor Rempe has invested many years working on systems in which single atoms are embedded in optical cavities. These cavities are composed of two highly reflecting mirrors placed at a very short distance. The emission of photons from an atom inside a cavity is directed and can therefore be sent to other network nodes in a controlled way. A photon entering the cavity is reflected between the mirrors several thousand times. In this way, the atom-photon interaction is strongly enhanced, and the atom can absorb the photon coherently and with high efficiency.

The first experimental challenge was to quasi-permanently trap the atom in the cavity. This was achieved via fine-tuned laser beams, meaning the least disturbance of the atom. In the next step, the physicists achieved controlled emission of single photons from the trapped atom. Finally, they could prove that the single-atom-cavity system represents a perfect interface for storing the information encoded in a single photon, and they were able to transfer it onto a second single photon after a certain storage time. The present work is another milestone on the way towards a large-scale quantum network. For the first time, two such systems were connected, and quantum information was exchanged between them with high efficiency and fidelity. The two systems, each representing a network node, are installed in two laboratories separated by 21 metres and are connected via a 60-metre long optical fibre.

Quantum networks exhibit peculiar properties not found in their classical counterparts. This is due to the fundamentally different behaviour of the exchanged information: while a classical bit represents either 1 or 0, a quantum bit can take both values at the same time, a phenomenon called “coherent superposition”. A measurement however projects the quantum bit onto one of the two values. In the single atom, the quantum information is encoded in a coherent superposition of two energy levels. When the atom at node A emits a photon, stimulated by a light pulses from a control laser, its quantum state is mapped onto the polarization state of the photon. Via the optical fibre the photon reaches node B where it is coherently absorbed. During this process, the quantum state originally prepared in atom A gets transferred onto the atom at node B. As a result, A is capable of receiving the next photon, while B is ready to send the stored information back to A or to any other node. It is this symmetric and reversible feature that makes the scheme scalable to arbitrary network configurations, consisting of many atom-cavity nodes. The atomic quantum states are read out by mapping them again onto the polarization of single photons which can easily be measured. “We were able to prove that the quantum states can be transferred much better than possible with any classical network. In fact, we demonstrate the feasibility of the theoretical approach developed by Professor Cirac,” Dr. Stephan Ritter, leader of the experiment, explains.

In yet another step the scientists succeeded in generating “quantum mechanical entanglement” between the two nodes. Entanglement is a feature unique to quantum objects. It connects them in such a way that their properties are strongly correlated in a non-trivial way, no matter how far they are separated in space. This phenomenon, predicted nearly a hundred years ago, was dubbed by Albert Einstein (who did not really believe in it) “spooky action at a distance”. In order to achieve entanglement between the two network nodes, the polarization of the single photon emitted by atom A is now entangled with the atomic quantum state. Once the photon gets absorbed, this entanglement gets transferred onto atom B. In fact, this is the first time that entanglement has been created between massive particles separated by such a large distance, making it the world’s “largest” quantum system with massive particles.
“We have realized the first prototype of a quantum network”, Stephan Ritter concludes. “We achieve reversible exchange of quantum information between the nodes. Furthermore, we can generate remote entanglement between the two nodes and keep it for about 100 microseconds, whereas the generation of the entanglement takes only about one microsecond. Entanglement of two systems separated by a large distance is a fascinating phenomenon in itself. However, it could also serve as a resource for the teleportation of quantum information. One day, this might not only make it possible to communicate quantum information over very large distances, but might enable an entire quantum internet.” Olivia Meyer-Streng

Original Publication:
Stephan Ritter, Christian Nölleke, Carolin Hahn, Andreas Reiserer, Andreas Neuzner, Manuel Uphoff, Martin Mücke, Eden Figueroa, Jörg Bochmann, and Gerhard Rempe
An elementary quantum network of single atoms in optical cavities
Nature, DOI: 10.1038/nature11023, 12 April 2012

Contact:
Prof. Dr. Gerhard Rempe
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching
Phone: +49 - 89 / 32905 -701
Fax: +49 - 89 / 32905 -311
E-mail: gerhard.rempe@mpq.mpg.de

Dr. Stephan Ritter
Max Planck Institute of Quantum Optics
Phone: +49 - 89 / 32905 -728
E-mail: stephan.ritter@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>