Bizarre matter could find use in quantum computers: Odd electron mix has fault-tolerant quantum registry

Bizarre matter could find use in quantum computers
From left, Rice physicist Rui-Rui Du, graduate students Chi Zhang and Yanhua Dai, and former postdoctoral researcher Tauno Knuuttila (not pictured) have found that odd groupings of ultracold electrons could be useful in making fault-tolerant quantum computers. Credit: Jeff Fitlow/Rice University

There are enticing new findings this week in the worldwide search for materials that support fault-tolerant quantum computing. New results from Rice University and Princeton University indicate that a bizarre state of matter that acts like a particle with one-quarter electron charge also has a "quantum registry" that is immune to information loss from external perturbations.

The research appeared online April 21 in . The team of physicists found that ultracold mixes of caught in magnetic traps could have the necessary properties for constructing fault-tolerant quantum computers -- future computers that could be far more powerful than today's computers. The mixes of electrons are dubbed "5/2 quantum Hall liquids" in reference to the unusual that describe their makeup.

"The big goal, the whole driving force, besides deep academic curiosity, is to build a quantum computer out of this," said the study's lead author Rui-Rui Du, professor of physics at Rice. "The key for that is whether these 5/2 liquids have 'topological' properties that would render them immune to the sorts of quantum perturbations that could cause information degradation in a quantum computer."

Du said the team's results indicate the 5/2 liquids have the desired properties. In the parlance of condensed-matter physics, they are said to represent a "non-Abelian" .

Non-Abelian is a mathematical term for a system with "noncommutative" properties. In math, commutative operations, like addition, are those that have the same outcome regardless of the order in which they are carried out. So, one plus two equals three, just as two plus one equals three. In daily life, commutative and noncommutative tasks are commonplace. For example, when doing the laundry, it doesn't matter if the detergent is added before the water or the water before the detergent, but it does matter if the clothes are washed before they're placed in the dryer.

"It will take a while to fully understand the complete implications of our results, but it is clear that we have nailed down the evidence for 'spin polarization,' which is one of the two necessary conditions that must be proved to show that the 5/2 liquids are non-Abelian," Du said. "Other research teams have been tackling the second condition, the one-quarter charge, in previous experiments."

The importance of the noncommutative quantum properties is best understood within the context of fault-tolerant quantum computers, a fundamentally new type of computer that hasn't been built yet.

Computers today are binary. Their electrical circuits, which can be open or closed, represent the ones and zeros in binary bits of information. In quantum computers, scientists hope to use "quantum bits," or qubits. Unlike binary ones and zeros, the qubits can be thought of as little arrows that represent the position of a bit of quantum matter. The arrow might represent a one if it points straight up or a zero if it points straight down, but it could also represent any number in between. In physics parlance, these arrows are called quantum "states." And for certain complex calculations, being able to represent information in many different states would present a great advantage over binary computing.

The upshot of the 5/2 liquids being non-Abelian is that they have a sort of "quantum registry," where information doesn't change due to external quantum .

"In a way, they have internal memory of their previous state," Du said.

The conditions needed to create the 5/2 liquids are extreme. At Rice, Tauno Knuuttila, a former postdoctoral research scientist in Du's group, spent several years building the "demagnetization refrigerator" needed to cool 5-millimeter squares of ultrapure semiconductors to within one-10,000th of a degree of absolute zero. It took a week for Knuuttila to simply cool the nearly one-ton instrument to the necessary temperature for the Rice experiments.

The gallium arsenide semiconductors used in the tests are the most pure on the planet. They were created by Loren Pfieiffer, Du's longtime collaborator at Princeton and Bell Labs. Rice graduate student Chi Zhang conducted additional tests at the National High Magnetic Field Laboratory in Tallahassee, Fla., to verify that the 5/2 liquid was spin- polarized.

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Apr 21, 2010
is it me or is this article written like a clifhanger in a series --- it leaves you saying --- okay .. and then....

it simply stops without explaining anything okay so they made a liquid with 5/2 spin -- then what did they do with it??

Apr 21, 2010
If it's non-Abelian, then therein lies the taking a different pathway, you won't come up w/ the same result - hence the fault tolerance.

yes, this is a REAL cliffhanger, b/z for a quantum computer, it would be ideal to have a storage medium (just like RAM or HD memory). A 5/2 quantum Hall system has a step-wise decay, not a continuous one. This is excellent for 2 really important reasons 1) It has 2n+1 possible eigenstates 2) a quantum Hall system displays voltage @ right angles to both the current and the B field. So, if they're correct, they can not only generate the 2n+1 superpositional values, they can also store them!!!! This would bring the many-body problem to it's knees!!!

Apr 21, 2010
In addition, if these quantum particles are truly non-Abelian *and* it is possible to entangle two or more of them and separate the entangled particles into remote and local systems, does this admit the possibility of an actualised instantaneous quantum communication of real-world information?

Disregarding for the moment difficulties of maintaining quantum-entangled states, if the prior state of the remote system is discoverable then presumably any change of state in the remote system, due to a change applied in the local entangled system, should also be discoverable. If so it ought to be able to be compared to the prior state and this information able to be used in a classical system?

Or possibly I have fundamentally misunderstood the implications of this article, as I always thought this communication concept to be impossible in practice. Is anyone able to clarify?

Apr 21, 2010
"Other research teams have been tackling the second condition, the one-quarter charge, in previous experiments."
Any relation to the hydrino?

Considering the very high degree of skepticism that hydrino's are even predicted by the theory proposed by the guy that suggests they exist, I would say probably not.

Apr 22, 2010
Anyone find it funny that "rice physicist" is an asian guy?

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