Diamonds engage at the nano scale

Manipulating the quantum properties of diamond impurities is a step closer to quantum computing, finer-scale microscopes.

The nearly-occult art of quantum computing research could soon help scientists in fields as remote as biology.

Two teams of researchers from the United States and Germany have found a way to essentially make diamond nanocrystals into microscopes that would see at the resolution of a single molecule. Such resolution could image the structure and motion of single molecules and reveal previously unseen inner workings of the living cell.

The researchers manipulated the quantum properties of single nitrogen atoms embedded in diamond crystals, turning the atoms into sensitive detectors of magnetic fields.

“It’s a real-world application of a quantum manipulation technique,” says Mikhail Lukin of HarvardUniversity, a member of one of the teams. Both teams report their results in the Oct. 2 Nature.

Daniel Rugar, a researcher at IBM’s AlmadenResearchCenter in San Jose, Calif., says the teams introduced an important new tool for exploring magnetic fields at the scale of nanometers, billionths of a meter. “It will be exciting to see how far this technique can be pushed,” he says.

Researchers have been studying diamond as a possible information storage space for future quantum computers, machines that could be enormously faster than ordinary computers because they would execute huge numbers of calculations simultaneously.

Diamond is promising because its rigid crystal structure of carbon atoms can shield each atom from outside disturbances — and it can do it at room temperature. A computer could then store information in a single atom, for example, by orienting the atom’s spin, the atomic analog of a bar magnet.

Researchers have been especially interested in nitrogen-vacancy centers, impurities in diamond that are single atoms of nitrogen sitting next to a gap in the carbon structure. Lukin and others have shown that the spin of an NV-center is easy to read and manipulate using laser pulses and radio-frequency waves.

In their study, Lukin and his collaborators show how a single NV-center in a diamond nanocrystal can detect magnetic fields as weak as one-ten-thousandth Earth’s magnetic field. Lukin first described the new technique in February at a Boston meeting of the American Association for the Advancement of Science (SN 3/1/08, p. 141).

In a separate paper, Fedor Jelezko of the University of Stuttgart in Germany and his collaborators describe how they placed a diamond nanocrystal on the tip of an atomic force microscope to scan the magnetic fields of cobalt nanoparticles.

Jelezko says that if the sensitivity improves — able, for example, to detect the spins of atomic nuclei — the technique could be used to resolve the structure of proteins that are hard to image using other techniques.

Jelezko says diamond nanocrystals could also be injected into cells, where the nanocrystals could, for example, attach to cellular membranes and monitor the passage of ions through the membranes or the changes in the shape of proteins bound to the membrane.

The diamond magnetometers don’t yet have the sensitivity or resolution of other types of magnetometers, including a microscopic cantilever that Rugar and his collaborators used to detect single electrons (SN 7/17/04, p. 37). Those techniques, however, require samples to be frozen and put in a vacuum, which makes them less practical, the researchers say.

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