Toward Room-Temperature Quantum Information Processing

Anne L. Fischer

Quantum spin states in semiconductors have generated considerable interest for their potential use in quantum information processing. By imaging and manipulating single electron spins in diamond crystals at room temperature, a group at the University of California, Santa Barbara, may have found a channel for transferring information to other surrounding electron spins.

The researchers initially were interested in the long-lived electronic spins of nitrogen-vacancy centers — defects consisting of only two atomic sites that exist in certain diamond crystals. Graduate students on the team developed an angle-resolved magneto-photoluminescence microscope to spot the individual defects and the small numbers of “dark” spins that cannot be detected by light emission. These particular dark spins come from surrounding nitrogen defects only a few nanometers away.

The confocal microscope, which provides high spatial resolution and uniquely precise angular control of the applied magnetic field at the diamond sample, can detect "dark" spins that cnanot be observed by light emission. Courtesy of David D. Awschalom.

According to research adviser David D. Awschalom, a professor of physics at the university, the microscope has high spatial resolution and sensitive feedback and can be stable for a week at a time, enabling the detection of a single spin over long durations. This is necessary for investigating the influence of both the angle and strength of the applied magnetic field.

Using the instrument, the scientists found that a channel opens up at very precise angles, whereby dark and bright spins interact at room temperature. This led them to believe that there may be ways to link electrons, which would be a big step toward quantum information processing. To build a quantum processor, Awschalom explained, one needs to make a network, so it must be possible to wire together quantum bits. The channel that the investigators discovered may be of use in making spin networks in which the dark spins would be used as wires.

The next step is to couple two spatially separated electron spins through the intermediate dark spins. The group has found an avenue to transfer spin information and is working to connect the dots.

Nature Physics, November 2005, pp. 94-98.