April 12, 2012
Quantum Network Created Based On Interfaces Between Single Atoms And Photons
Brett Smith for Redorbit.com
Quantum physicists have made a leap forward in subatomic particle communication by connecting two separate labs 21-meters apart using two atoms and a photon, according to a report published in the April 12 issue of Nature.A group from the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany said they have demonstrated the ability to construct a basic two-node network that could be expanded because of its high efficiency and fidelity.
“This approach to quantum networking is particularly promising because it provides a clear perspective for scalability”, Professor Gerhard Rempe noted.
The experimental network´s quantum bits, or qubits, are different from traditional bits used in today´s electronics that can only store two unique values: 0 or 1. A quantum bit can share both of these values at the same time due to a phenomenon called “coherent superposition.” This possibility means that quantum based communication could become vastly superior to the systems currently in place.
To demonstrate this basic level of communication, scientists constructed nodes, or qubits, by trapping a single rubidium atom in a reflective optical cavity. The two nodes were connected via an optical fiber between the two labs. Communication occurred when one of the atoms emitted a single photon, whose polarization state carried the mark of its parent atom's quantum state, along the length of the fiber. The atom at the other node absorbed the photon from the fiber–causing it to switch to the quantum state imprinted on that photon's polarization.
The scientists also demonstrated the ability to achieve “quantum mechanical entanglement” between the two nodes. This state, which is unique to quantum objects, connects the two nodes in such a way that their properties are strongly correlated, regardless of distance. Manipulation of either node affects both, making for a highly efficient exchange of information across great distances, the cornerstone of any great network from the pony express to the telegraph. Albert Einstein, who did not fully support the possibility of quantum mechanical entanglement, called the phenomenon “spooky action at a distance.”
Previously, scientists have been able to perform various elements of the quantum network, such as the construction of a rudimentary two-qubit quantum processor .The MPQ team was the first to be able to employ the separate technologies in concert to form the network.
MPQ physicist Steven Ritter acknowledged that the prototype network has many flaw and deficiencies that must be worked out before quantum information exchange can be put into use. He also described a bright future for this emerging technology.
“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.”
Image Caption: 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)