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  • Teleporting a step closer to quantum computing

Photonics Spectra
Mar 2009
Hank Hogan,

COLLEGE PARK, Md. – It’s not “Star Trek,” but it does seem like science fiction. Researchers from the Joint Quantum Institute at the University of Maryland have for the first time teleported information from one atom to another at a distance of 1 m, without the data passing through any physical medium. Because atoms can store quantum bits – or qubits – the technique could be used to hold and manage quantum data over long distances, something not feasible before.

For the first time, researchers have stored information in one trapped atom (below), then teleported it across a distance of 1 m (diagrammed on right; setup shown on next page) to a different atom. Images courtesy of Curt Suplee, Joint Quantum Institute and the University of Maryland.

“This is a new way to pipe around quantum information,” said physics professor and research team leader Christopher Monroe. Such long-distance quantum communication theoretically would be completely secure and immune to eavesdropping. Attempts at quantum communication are in their infancy, limited in part by short-range capabilities. Other uses of the new technique include multiparty communications in something akin to a quantum Internet or in quantum computing, which, because of its nature, can solve certain problems that classical computing cannot handle practically.

These applications are possible, in part, because a qubit, unlike a classical bit, is a superposition of two or more states. A qubit remains in this combination of yes and no until a measurement is made.

In demonstrating its scheme, Moore’s team used two ytterbium ions, holding them in unconnected vacuum traps separated by about 1 m. At the start of the process, the investigators initialized each ion using a microsecond-long pulse of 369.5-nm light from a frequency-doubled amplified diode laser. They applied a resonant microwave burst of a controlled phase and duration to put the first ion in the qubit state to be teleported to the second ion.

They then fired a picosecond-long laser pulse at both ions. Each ion emitted a single photon correlated to the originating atom’s qubit state. After capturing the emitted photons and routing them through a 50/50 beamsplitter, they recorded their arrival at one or both of two detectors. The latter case signaled when the two atoms were entangled, with their properties intertwined. When that happened, the researchers measured the qubit state of the first ion, which provided them the ability to recover information from the second ion that had been stored in the first.

PNTeleport_Fig-3_Optional.jpgGiven the entanglement signal, the method faithfully teleports information with 90 percent accuracy, the group reported in the January 23 issue of Science. A drawback is that the entanglement signal occurred only a little more than twice every hundred million attempts. The researchers overcame this low probability by repeating the entire procedure tens of thousands of times per second. Even with that, entanglement was detected only every 12 minutes.

In scaling up to a larger number of atomic nodes, the likelihood of detecting entanglement must be increased, and Monroe said the group is working on this. “We have some ideas [about] how to add several orders of magnitude to the success probability of getting those photons into fibers and detected.”

An electromagnetic wave lying within the region of the frequency spectrum that is between about 1000 MHz (1 GHz) and 100,000 MHz (100 GHz). This is equivalent to the wavelength spectrum that is between one millimeter and one meter, and is also referred to as the infrared and short wave spectrum.
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