Lasers can be used to lengthen quantum bit memory by 1,000 times

WASHINGTON - Physicists have found that lasers can be used to drastically prolong the shelf life of quantum bit memory, the 0s and 1s of quantum computers, by 1,000 times. These precarious bits, formed in this case by arrays of semiconductor quantum dots containing a single extra electron, are easily perturbed by magnetic field fluctuations from the nuclei of the atoms creating the quantum dot.

This perturbation causes the bits to essentially forget the piece of information they were tasked with storing.

A quantum dot is a semiconductor nanostructure that is one candidate for creating quantum bits.

The scientists, including the University of Michigan’s Duncan Steel, used lasers to elicit a previously undiscovered natural feedback reaction that stabilizes the quantum dot’s magnetic field, lengthening the stable existence of the quantum bit by several orders of magnitude, or more than 1,000 times.

Because of their ability to represent multiple states simultaneously, quantum computers could theoretically factor numbers dramatically faster and with smaller computers than conventional computers.

For this reason, they could vastly improve computer security.

“In our approach, the quantum bit for information storage is an electron spin confined to a single dot in a semiconductor like indium arsenide,” said Steel.

“One of the serious problems in quantum computing is that anything that disturbs the phase of one of these spins relative to the other causes a loss of coherence and destroys the information that was stored,” he added.

A major cause of information loss in a popular class of semiconductors called 3/5 materials is the interaction of the electron (the quantum bit) with the nuclei of the atoms in the quantum dot holding the electron.

Trapping the electron in a particular spin, as is necessary in quantum computers, gives rise to a small magnetic field that couples with the magnetic field in the nuclei and breaks down the memory in a few billionths of a second.

By exciting the quantum dot with a laser, the scientists were able to block the interaction of these magnetic fields.

The laser causes an electron in the quantum dot to jump to a higher energy level, leaving behind a charged hole in the electron cloud.

This hole, or space vacated by an electron, also has a magnetic field due to the collective spin of the remaining electron cloud.

It turns out that the hole acts directly with the nuclei and controls its magnetic field without any intervention from outside except the fixed excitation by the lasers to create the hole. (ANI)