PORTLAND, Ore. Georgia Tech researchers are claiming a 200-fold increase in quantum memory storage times, making the technology feasible for secure, long-distance quantum networking.
The researchers demonstrated "refresh times" of seven milliseconds, only a tenth as long as DRAMs refresh rates (64 milliseconds), but well within the range required for optical repeaters.
Quantum states encode data on single photons which are almost impossible to hack without alerting the receiver, thereby enabling ultra-secure networks. But the short refresh time of current quantum mechanisms have limited them to point-to-point connections.
For long-distance quantum networks, repeaters are required to extend range. Complex, experimental repeaters have been designed, but have yet to be proven in working systems. By extending the refresh time for quantum memories into the millisecond realm, the Georgia Tech researchers may have made repeaters much easier to implement.
For future long-distance quantum networks, lasers will encode quantum bits (qubits) during the polarization of individual photons, which then travel along optical fibers between repeaters spaced about every 100 kilometers (328 miles). At the repeater, qubits are stored for a few milliseconds, then read out and sent to the next leg of the optical network.
The researchers claim their technique could be used for temporary storage, but caution that it could take 10 years to perfect the technique outside the laboratory
They beat the previous record for storing and retrieving quantum information--32 microseconds--using a dipole optical trap composed of supercooled rubidium atoms held in place with laser beams configured in a one-dimensional optical lattice. The team also minimized interference from magnetic fields by pumping the atoms into the clock transition state, which is relatively immune to magnetism
The qubits were stored by encoding their state with a laser beam onto the collective excitation of the cold rubidium atoms, thereby storing the qubit's polarization information. Milliseconds later, a second laser reads out qubits from the atoms and re-encodes them onto the polarization of a new photon. In working networks, the new photon would be sent to a second fiber and on to the next repeater.
Funding was provided by the National Science Foundation, the A.P. Sloan Foundation and the U.S. Office of Naval Research.