New way to distance quantum entanglement
Friday, March 25, 2011
(Photo: UAM)
Researchers at the Autonomous University of Madrid (UAM) and the Institute of Materials Science of Aragon (ICMA-CSIC) have proposed a new technique to get two physically separated quantum systems can be entangled. The technique, based on theory of plasmons, is promising in areas such as computing, cryptography and quantum teleportation.
Quantum entanglement is a property predicted in 1935 by Einstein, Podolsky and Rosen in their formulation of the so-called EPR paradox. This is a phenomenon in which the quantum states of two or more objects must be described with reference to the quantum states of all objects in the system, even if the objects are spatially separated.
This phenomenon has place in recent years some interesting reflections in the field of fundamental physics as well as promising applications in quantum computing, quantum cryptography and quantum teleportation. However, long-distance entanglement between quantum entities still remains a key scientific challenge. The usual route to overcome this problem has been the photonics: the control of light particles. But now researchers at the UAM and ICMA propose a better alternative: plasmonics. In its proposal, published in the journal Physical Review Letters, a surface plasmon mode acts as a mediating agent of entanglement between two systems quantum located on opposite edges of a slot made in a silver film. Through the confinement of light in the plasmonic waveguide, a large fraction of the radiation emitted by a quantum system is captured by the proper manner of waveguide and transferred to another system.
The researchers derived analytical expressions for coherent and incoherent parts of the interactions. An appropriate phase difference between these two components to disconnect one of the two contributions, while maximizing the other by varying the divide between the systems. This allows a route plasmon entanglement of quantum systems at distances larger than the wavelength of operation of the device. 
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