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Oct 1st, 2010
Quantum signals converted to Telecom wavelengths
Using optically dense, ultracold clouds of rubidium atoms, three key elements needed for quantum information systems have been advanced — including a technique for converting photons carrying quantum data to wavelengths that can be transmitted long distances on optical fiber telecom networks.
The developments move quantum information networks — which securely encode information by entangling photons and atoms — closer to a possible prototype system.
Fig1: Associate professor Alex Kuzmich with equipment used to study quantum information systems at the Georgia Institute of Technology. (Photos: Gary Meek)
"This is the first system in which such a long memory time has been integrated with the ability to transmit at telecom wavelengths," said Brian Kennedy, a co-author of the Nature Physics paper and a professor in the Georgia Tech School of Physics. "We now have the crucial aspects needed for a quantum repeater."
Fig2: Experimental equipment used to study quantum information systems at Georgia Tech.
"One photon of infrared light going in becomes one photon of telecom light going out," said Alex Kuzmich, an associate professor in the Georgia Tech School of Physics and another of the paper's co-authors. "To preserve the quantum entanglement, our conversion is done at very high efficiency and with low noise."
Fig3: Researchers Alex Radnaev and Jacob Blumoff (standing) and Yaroslav Dudin collect data for a study of quantum information systems at the Georgia Institute of Technology.
Once the photons are converted to telecom wavelengths, they move through optical fiber — and loop back into the magneto-optical trap. They are then converted back to infrared wavelengths for testing to verify that the entanglement has been maintained. That second conversion turns the rubidium cloud into a photon detector that is both efficient and low in noise, Kuzmich said.
Because of loss in the optical fiber that makes up these networks, repeaters must be installed at regular intervals to boost the signals. For carrying qubits, these repeaters will need quantum memory to receive the photonic signal, store it briefly, and then produce another signal that will carry the data to the next node, and on to its final destination.
For more information, visit: www.gatech.edu
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