This is cool:

Diamond is cool—even at room temperature. The stiff crystalline structure that makes diamond nature’s hardest material can shield an atom from heat vibrations—not forever, but a lot longer than in other materials.

Physicists have now learned to use that ultimate cocoon quality to store and manipulate information in single atoms at room temperature—feats that in other materials require getting to the neighborhood of absolute zero. Because its atoms can store the notoriously peculiar quantum information, diamond has become a candidate material for use in future quantum computers. Such devices would rely on quantum weirdness to perform certain tasks that would take an ordinary computer till the end of time.

Diamond, specifically artificial diamond, could also find more imminent applications, such as communicating data with unbreakable encryption or even advancing the understanding of quantum theory itself. Powering these applications would require just tiny artificial-diamond chips along with inexpensive tools such as simple lasers.

“The beauty of diamond is that it brings all of this physics to a desktop,” says David Awschalom of the University of California, Santa Barbara (UCSB).

Diamonds can be sharp cutters, but from the point of view of ordinary electronics, they are pretty dull, at least in their purest form. Diamond’s crystal lattice of carbon atoms doesn’t conduct electricity and has virtually no magnetism. There’s no such thing as a 100 percent-pure crystal, though, and diamond’s impurities are in fact Marilyn Monroe beauty marks that make it attractive for physics. “It’s the dirt that gives rise to the unusual properties,” Awschalom said during a recent talk in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS).

Nitrogen is the most common impurity in diamond, where it can replace a carbon atom in the crystal. The most useful nitrogen impurities are those that happen to be next to a vacancy—a gap in the crystal where a carbon would otherwise be.

Two of the nitrogen’s electrons stretch their orbits into the vacancy and form a moleculelike structure, even though one of the molecule’s atoms is missing. This virtual molecule, called a nitrogen-vacancy (NV) center, possesses spin, the quantum form of magnetism.

Spins are like microscopic bar magnets and can encode and store information by pointing in different directions. A single unit of information, called a bit, can be, say, a 1 if the spin points up or a 0 if it points down.

Spins can also be simultaneously up and down, and in such cases are said to be in special “quantum states.” Quantum states contain quantum bits of information, or qubits. A quantum computer could perform calculations using the multiple states of qubits, which is essentially like doing several calculations at the same time. That might enable it, for example, to search databases or to find prime factors of whole numbers at speeds unattainable with ordinary computers.

But quantum states are notoriously delicate, and even a small disturbance can result in the complete loss of the information stored in a qubit. Researchers have so far managed to store and manipulate only a handful of qubits in superbly well-controlled systems, such as single ions suspended in an electromagnetic trap or superconducting materials cooled to very low temperatures. In a paper to be published in Science, Awschalom and his collaborators describe how they achieved a similar level of control over NV centers in diamond.

In addition to having a spin, NV centers have a unique way of standing out in the limelight. They have a signature response to light, meaning that they will fluoresce with blue or green light when the rest of the material doesn’t. Typically, they are also few and far between—spaced by micrometers—so that they can be spotted individually using an optical microscope and a sensitive light detector.

Jörg Wrachtrup, now at the University of Stuttgart in Germany, and his collaborators first imaged single NV centers in diamond in 1997. The researchers first tried at cold temperatures, where NV centers were supposedly easier to isolate. That didn’t work. But when the researchers let temperatures go up, they were startled to see the NV centers’ light begin to stand out from a noisy background of scattered light.

In their recent experiments, Awschalom and his team explored for the first time the full extent to which they could manipulate the states of NV centers. The researchers zeroed in on a single NV center. They used a laser pulse to kick the NV center’s electrons down to a known, lowest-energy state, readying it to record a qubit. They then tickled its spin gently using microwave radiation. The spin took different mathematical combinations of three simultaneous directions, thereby simultaneously encoding different information, explains Awschalom’s colleague Adrian Feiguin, part of the Microsoft Corp. research team at UCSB. With a second laser pulse, the researchers also made the NV center fluoresce, so they could measure its state at different times, essentially reading out the information.

At the same time, the NV center also felt the presence of other spins nearby, just like several bar magnets will exert magnetic forces on each other when they’re close together. The other impurities were mostly “dark” nitrogen atoms, meaning that they were not fluorescing because they were not paired with vacancies. In principle, all spins in a small region of a solid can influence one another, and the team needed to test how such a web of interactions would affect the information stored in their NV center qubit.

The team expected that in some cases the NV center would quickly lose its quantum weirdness, and go from its multiple states to a well-defined single state, like any macroscopic object. What the researchers found was …

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