Lasers keep quantum bits from dying before their time

Quantum computing developements come fast and furious

The heart and sole of quantum computing - its quantum bits - tend to have a short shelf life but scientists are looking at a way to keep them around longer.  Physicists have found a way to drastically prolong the shelf life of quantum bits, the 0s and 1s of quantum computers, letting them keep and act on data longer.  

The scientists used lasers to elicit a previously undiscovered reaction that stabilizes the magnetic field of what's know as the quantum dot, which is a semiconductor nanostructure that is used to create quantum bits.  That action enables the stable existence of the quantum bit by several orders of magnitude, or more than 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 agitation causes the bits to essentially forget the piece of information they were tasked with storing.

"In our approach, the quantum bit for information storage is an electron spin confined to a single dot in a semiconductor like indium arsenide. Rather than representing a 0 or a 1 as a transistor does in a classical computer, a quantum bit can be a linear combination of 0 and 1. It's sort of like hitting two piano keys at the same time," said Duncan Steel, a professor in the University of Michigan's Department of Physics said in a release.

"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. It is as though one of the two notes on the piano is silenced, leaving only the other note," he said.

Researchers said spin is an property of the electron that  is like magnetic poles. Electrons are said to have spin up or down, which represent the 0s and 1s, the researchers said.

Quantum computing developments have come fast and furious in recent months.

Earlier this year researchers touted what they call a quantum buffer, technology that could be used to control the data flow inside a quantum computer. The research envelopes work with the sometimes other-worldly science known as quantum entanglement. Quantum entanglement is developing component of quantum physics that looks at the behavior between atoms and  photons that could ultimately play a key role in developing security, unbelievably fast networks and even teleportation. 

In the new research, scientists from the Joint Quantum Institute (JQI) of the Commerce Department's National Institute of Standards and Technology (NIST) and the University of Maryland each quantum image is carried by a light beam and consists of up to 100 pixels. A pixel in one quantum image displays random and unpredictable changes say, in intensity, yet the corresponding pixel in the other image exhibits identical intensity fluctuations at the same time, and these fluctuations are independent from fluctuations in other pixels, researchers stated.

By using a gas cell to slow down one of the light beams to 500 times slower than the speed of light, the group has demonstrated that they could delay the arrival time of one of the entangled images at a detector by up to 27 nanoseconds. The correlations between the two entangled images still occur-but they are out of sync. A flicker in the first image would have a corresponding flicker in the slowed-down image up to 27 nanoseconds later.

In their experiment, the researchers sent one of the entangled light beams through a second cell of rubidium gas where a similar four-wave mixing process is used to slow down the beam. The beam is slowed down as a result of the light being absorbed and re-emitted repeatedly in the gas. The amount of delay caused by the gas cell can be controlled by changing the temperature of the cell (by modifying the density of the gas atoms) and also by changing the intensity of the pump beam for the second cell, researchers stated.

The demonstration showed that this type of quantum buffer could be particularly useful for quantum computers, both in its information capacity and its potential to deliver data at precisely defined times, researchers said.

Also this year, with matching funds from the province of Ontario and RIM founder Mike Lazaridis, University of Waterloo's Institute for Quantum Computing will receive $150 million to build a research facility and attract talent. Canada will become home to the largest concentration of quantum computing talent in the world, thanks to $150 million in funding from government and the founder of Research In Motion Ltd

Last Fall, the US Army Research Office and the National Security Agency (NSA) said they were looking for some answers to their quantum physics questions.

Specifically the agencies are soliciting proposals to achieve three broad goals:

-develop new quantum computing algorithms for hard computational problems;

-characterize the efficiency of candidate quantum algorithms;

-develop insights into the power of quantum computation and consider issues of quantum complexity and computability.

Also in September, researchers at (NIST) demonstrated a technique that could make quantum cryptography significantly cheaper to implement, moving it nearer to possible commercial acceptance.  The technique is aimed at cutting the cost of equipment needed for quantum key distribution (QKD), designed to distribute cryptographic keys using a secure system based on the principles of quantum mechanics.

And of course the Defense Advanced Research Projects Agency is looking for  research in the quantum entanglement arena. DARPA's program, called Quantum Entanglement Science and Technology (QuEST) has the lofty goal of developing revolutionary advances in the fundamental understanding of quantum information science, DARPA said.

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