Wednesday, December 07, 2005

A Step Towards Quantum Computing

In the latest edition of the scientific journal Nature, researchers at Georgia Tech have demonstrated a key step in the pursuit of quantum computing. Here is the abstract:

"Nature 438, 833-836 (8 December 2005) doi:10.1038/nature04315

Storage and retrieval of single photons transmitted between remote quantum memories
T. Chanelière1, D. N. Matsukevich1, S. D. Jenkins1, S.-Y. Lan1, T. A. B. Kennedy1 and A. Kuzmich1

An elementary quantum network operation involves storing a qubit state in an atomic quantum memory node, and then retrieving and transporting the information through a single photon excitation to a remote quantum memory node for further storage or analysis. Implementations of quantum network operations are thus conditioned on the ability to realize matter-to-light and/or light-to-matter quantum state mappings. Here we report the generation, transmission, storage and retrieval of single quanta using two remote atomic ensembles. A single photon is generated from a cold atomic ensemble at one site 1, and is directed to another site through 100 metres of optical fibre. The photon is then converted into a single collective atomic excitation using a dark-state polariton approach2. After a programmable storage time, the atomic excitation is converted back into a single photon. This is demonstrated experimentally, for a storage time of 0.5 microseconds, by measurement of an anti-correlation parameter. Storage times exceeding ten microseconds are observed by intensity cross-correlation measurements. This storage period is two orders of magnitude longer than the time required to achieve conversion between photonic and atomic quanta. The controlled transfer of single quanta between remote quantum memories constitutes an important step towards distributed quantum networks."

Quantum computing takes advantage of things like quantum spin states, which are only allowed to have very specific values, in order to create qubits, which play the role of normal bits (binary digits) in computer coding (strings of 1's and 0's). One problem has been trying to reproduce and store the same information in a network, which appears to have been solved by this group. Quantum computing, encryption, and other technologies that utilize quantum mechanical systems have long been sought, and I suspect it is a matter of time before the next big step in computational technology becomes a reality.

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