Quantum dots could bridge gap between electronic and quantum computers

Quantum computing
Stef Simmons (CC-BY 2.0)

An intriguing type of quantum computing is one step closer to practicality with the announcement today that experts at the Los Alamos National Laboratory, Stanford University and the Technical University of Munich have managed to solve one of the technology’s major problems using common semiconductor materials.

The idea behind quantum computing, in the broadest possible strokes, is to use the quantum state of a small particle to store information. The advantage is that each of these particles, called qubits, can store a large range of values, while the regular bits at the core of electronic computers can only represent zero or one. Consequently, the theory goes, certain kinds of computation could be performed at vastly superior speeds.

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The actual particles to be used as qubits vary – some proposed quantum computers use photons, others ions or other atoms that can be manipulated to represent different values. But the announcement made today details a quantum computer that uses a lone electron enclosed in a nanostructure, called a quantum dot, made from standard semiconductor materials to store information in the form of the electron’s spin.

Previously, the use of the technique had been limited by what Technical University of Munich researcher Alexander Bechtold described in the announcement as a piezoelectric effect, which caused the spin state to fluctuate – meaning that the information stored is corrupted in a matter of hundreds of nanoseconds.

The fix? Magnets, according to Bechtold. A magnetic field of 1.5 teslas apparently counteracts this loss of information.

“This corresponds to the magnetic field strength of a strong permanent magnet,” he said. “It stabilizes the nuclear spins and the encoded information remains intact.”

The Munich research group’s leader, Jonathan Finley, said that these semiconductor quantum dots are an “extremely promising” system, and that they have a particular, unique upside.

“The semiconductor quantum dots have the advantage that they harmonize perfectly with existing computer technology since they are made of similar semiconductor material,” he said in the announcement.

The group’s findings have been published in the journal Nature, and they’re not the only ones making quantum computing headway with work based on existing computer technology. Australian researchers recently developed the first quantum logic gate in silicon, paving the way for functioning quantum computers made from that material, and Microsoft open-sourced a programming framework designed to simulate how a quantum computer operates last week.

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