Quantum computing could enable computers to solve much more complex problems much more quickly than ever before. There are a lot of unanswered questions, though, when it comes to quantum bits, the base logical elements of quantum processing. One team of researchers has demonstrated some processes that show how information can be retained using quantum bits, all in a system that can be made out of standard semiconductor materials.

A group of researchers including physicists from the Technical University of Munich, the Los Alamos National Laboratory, and Stanford University have studied how data can be lost in a quantum bit system and developed a new method for retaining it.

“Overall, the system is extremely promising,” said Jonathan Finley, head of the research group along with Alexander Bechtold. “The semiconductor quantum dots have the advantage that they harmonize perfectly with existing computer technology since they are made of similar semiconductor material.”  

Quantum bits can be used to store information just like confined ions or atoms can. However, the question was how long information could be stored in them and how that information might be lost.

The quantum bits used in this experiment were formed by evaporating indium gallium arsenide onto a gallium arsenide substrate, forming a nanostructure with nanometer-scale “hills” called quantum dots.

A single electron is trapped in each of the quantum dots, and the spin state of this electron can then be used for information storage and read by laser pulses.

The problem with this method was that strain in the semiconductor material leads to loss of quantum information. Uncontrolled fluctuations in the nuclear spin modifies the spin of the electron, making its encoding useless. This loss was poorly understood, but Finley’s group found that losses can be reduced by applying a magnetic field.

Data can also be lost due to the effect the surrounding atomic nuclei have on the electron spin.

“However, both loss channels can be switched off when a magnetic field of around 1.5 tesla is applied,” said Bechtold. “This corresponds to the magnetic field strength of a strong permanent magnet. It stabilizes the nuclear spins and the encoded information remains intact.”

By providing proof of both of these loss mechanisms and a solution, the team could push forward the use of quantum dots in information processing.

Their research was published in the journal Nature.