Light step toward quantum networks.

Researchers are striving to use quantum physics to store, manipulate, and transmit data to someday create extraordinarily powerful and secure computer networks. Now, physicists in Atlanta have demonstrated the quantum version of one of the most basic network functions: reading a bit from a computer's memory so that it can be sent through a communications channel.

Dzmitry N. Matsukevich and Alex Kuzmich of the Georgia Institute of Technology describe the feat in the Oct. 22 Science.

Unlike conventional bit reading, the procedure manipulates quantum data bits, or qubits, which can each simultaneously represent a 0 and a 1. In a likely architecture for quantum networks, individual or small aggregates of atoms or ions will act as qubits for storage and calculations, whereas photons will serve as communications qubits between the atoms or ions.

In the new experiment, the researchers forced a cloud of ultracold rubidium-85 atoms into a specific quantum state. Then, they triggered those atoms to collectively emit one photon endowed with its own version of the cloud's quantum state.

"For the first time ... we've transferred a matter qubit to a photon qubit," Kuzmich says. Next to come, he adds, is the converse operation. --P.W.