Scientists at the University of Michigan (Ann Arbor, MI) have stored and retrieved information through quantum phase in N-state Rydberg atoms in a single operation, storing numbers as large as 27. In the experiment, three optical pulses intersect a beam of cesium atoms. A 10-ns, 1080-nm pulse excites the atoms to the proper state. A second 150-fs, 785-nm chirped pulse with computer-controlled shape from a Ti:sapphire laser programs the quantum register of the atoms by setting the phase of each quantum state, while a third pulse similar to the second then searches for the information. The number is read out by applying a ramped electric field and measuring the field's value at the instant of ionization.
The readout pulse must arrive within several nanoseconds of the programming pulse. The minimum number of atoms required for storage of a single bit is on the order of 100. When a computer-generated random number of size 2N-1 is programmed and then read out, correct retrieval occurs 96% of the time for N = 6, and 80% for N = 8. It may be possible to store numbers as large as 2100, say the researchers. Contact Philip Bucksbaum at [email protected].