Diamonds in Quantum Computing

Quantum particles have the bizarre capacity to contain a variety of different states at once. This is called superposition. A quantum particle may be in a superposition of states but it will break down into one of those states once it is observed. In fact, it will break down if the particle interacts too much with the external environment.

This delicate property makes the quantum world appealing to computer scientists. By exploiting superposition, many different mathematical values may be explored simultaneously. That would make computers thousands of times faster and solve mathematical problems that are too complex for classical machines. But the difficulty of keeping those quantum bits in causal isolation is a huge technical challenge. Often, it has required cooling materials close to absolute zero.

Diamond is now showing promise as a material that can perform quantum computing functions at room temperature. "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.

Science News posts an article about how diamonds -- or more precisely, flaws in diamonds -- are showing promise. In a natural diamond lattice, flaws are inevitable. The most common impurity is a nitrogen atom. Another kind of flaw is a vacancy in the lattice where a carbon would otherwise sit.

When a diamond crystal contains a nitrogen and a vacancy next to each other, something strange happens. Electrons from the nitrogen will orbit the vacancy as though an atom is there.

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.

...Researchers have so far managed to store and manipulate only a handful of qubits [quantum bits] 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.

The October 2007 issue of Scientific American had an excellent article on this research [subscription]:

Diamond has a track record of extremes, including ultrahardness, higher thermal conductivity than any other solid material and transparency to ultraviolet light. In addition, diamond has recently become much more attractive for solid-state electronics, with the development of techniques to grow high-purity, single-crystal synthetic diamonds and insert suitable impurities into them (doping). Pure diamond is an electrical insulator, but doped, it can become a semiconductor with exceptional properties. It could be used for detecting ultraviolet light, ultraviolet light-emitting diodes and optics, and high-power microwave electronics. But the application that has many researchers excited is quantum spintronics, which could lead to a practical quantum computer—capable of feats believed impossible for regular computers—and ultra­secure communication.

Scientific American on the Large Hadron Collider

The Large Hadron Collider (LHC) is set to go online later this year. Scientific American printed a great series of articles on the LHC in their February 2008 issue. Non-subscribers can access two of the main articles online:

Large Hadron Collider: The Discovery Machine and
The Coming Revolution in Particle Physics

Here's a taste of what to expect from the first article:

[T]he LHC’s basic parameters outdo those of previous colliders in almost every respect. It starts by producing proton beams of far higher energies than ever before. Its nearly 7,000 magnets, chilled by liquid helium to less than two kelvins to make them superconducting, will steer and focus two beams of protons traveling within a millionth of a percent of the speed of light. Each proton will have about 7 TeV of energy—7,000 times as much energy as a proton at rest has embodied in its mass, courtesy of Einstein’s E = mc2. That is about seven times the energy of the reigning record holder, the Tevatron collider at Fermi National Accelerator Laboratory in Batavia, Ill. Equally important, the machine is designed to produce beams with 40 times the intensity, or luminosity, of the Tevatron’s beams. When it is fully loaded and at maximum energy, all the circulating particles will carry energy roughly equal to the kinetic energy of about 900 cars traveling at 100 kilometers per hour..."

The picture on the right is of the Compact Muon Solenoid (CMS). It is one of the four experiments built into the LHC. The other experiments are ALICE, ATLAS and LHCb.