The tiny computer, created by researchers from the University of Southern California, Delft University of Technology in The Netherlands, Iowa State University, and the University of California, Santa Barbara features a pair of quantum bits, or qubits, composed of subatomic particles, the team reported in the current issue of Nature.
Quantum computing, first proposed by the Nobel Prize-winning physicist Richard Feynman in 1981, is still highly theoretical, with experiments in the science and its cousin, quantum cryptography, limited to laboratory settings thus far. In other words, there are no practical quantum computers yet, just experimental ones.
The basic concept is to use the odd nature of the entangled qubits that one uses to build a quantum computer to perform computational tasks much faster and much more securely than is possible on digital computers that use silicon transistors.
The use of a solid-state material, in this case a diamond, means that unlike other attempts to build a quantum computer out of gases or liquids, this system could potentially be scaled up in size to achieve computational speeds that rival traditional computers, the researchers said.
The diamond-based quantum computer also is the first of its kind to protect against quantum decoherence, the loss of information from a subatomic system—like entangled qubits in a quantum computer—into the environment, lead researcher Daniel Lidar of USCtold USC News on Thursday.
The team's quantum computer uses the nucleus of a nitrogen atom as one qubit and an electron as the other. Each subatomic particle has a benefit and a drawback, Lidar said—a nucleus has a slow rate of decoherence but is also fairly sluggish at performing computations, while an electron is a number-crunching speedster but is much more unstable.
The nucleus and electron themselves aren't actually the qubits, Lidar explained. Instead, it's the spin of the particles that should be considered as driving a quantum computer. The way the team was able to offset the decoherence problem was by shooting a steady stream of microwave pulses at the electron to reset the direction of its spin rotation, which the scientist described as "a little like time travel."
The researchers were able to demonstrate the tiny diamond computer performing a search of an unsorted database of four choices (a test of "Grover's algorithm") with results they said showed it was operating in a quantum fashion. While a non-quantum search of such a database for a single, correct item of data would, on average, yield the correct answers after two tries, a quantum computer should be able to get the answer right the first time, every time.
The team's diamond-based quantum computer made the correct choice on its first try 95 percent of the time, Lidar said.
Other researchers around the world have produced some encouraging results in quantum computing and related fields over the past few months. In February, scientists in Australiafashioned a working transistor from a single atom and later that same month, IBM scientists said they'd worked out several kinks and were "close to the minimum requirements for a full-scale quantum computing system as determined by the world-wide research community."
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