Lunch & Learn: Toward Quantum Computing with Zahid Hasan

ICboard.jpgImagine a computer that made direct use of quantum mechanical phenomena. Such a machine would likely operate exponentially faster than our present computers.
Zahid Hasan is leading an international scientific collaboration that has observed an exciting and strange behavior in electrons’ spin within a new material that could be harnessed to transform computing and electronics. The team believes that the discovery is an advance in the fundamental physics of quantum systems and could lead to significant progress in electronics, computing and information science.
The team has been searching for a material whose atoms, when placed in certain configurations, would trigger electrons to produce exotic “quantum” effects. In the Feb. 13 issue of Science, the team reported that the quantum Hall effect, a phenomena in condensed-matter physics, can occur within a carefully constructed crystal made of an antimony alloy laced with bismuth. The behavior involves a strange form of rotation that could potentially transform computing and storage.


At the December 10 Lunch ‘n Learn, Hasan explained that the team had observed a fundamentally new quantum phase of matter which, among other things, can be used for topological quantum computing within a device geometry.
Looking back through time, he noted that once we determined the physics of the semi-conductors and transistors to store 0s and 1s, we were then able to build modern computers. In order to create a quantum computer, we need physics that will permit us to build analogous logic systems. In other words, to go beyond conventional computing, to implement the logic of the quantum world in a microscopic sense, Dr. Hasan and his team have had to confront what sort of physics is needed to implement the new logic in a quantum world.
Past efforts have focused upon superconductor based Josephson junctions, trapped ions, and quantum dots, but all three approaches have run up against a fundamental problem. Any attempt to bring the results back to the classical world inevitably interacts with its environment and causes decoherence, the loss or distortion of the information.
HallEffect.jpg

In 1879 Edwin Hall discovered that there is a perpendicular difference in electrical voltage across an electrical conductor. The result is that electrons are pushed to the edge of the conductor. The team reports that they have been able to create a Quantum Hall effect in their new crystal, and to take pictures of the dancing patterns of electrons on the edges of their sample. Subjecting the new materials to temperatures in the range of 4 degree Kelvin, the team observed exotic behaviors without the presence of any external magnetic field. Hasan hopes that, within the next two decades, such advances may lead to remarkably fast computing devices.
ZahidHasan.jpgUnlike our present machines, which are limited to a choice of a “0” or a “1,” quantum machines may be able to register an infinite number of possibilities. A quantum computer with n qubits could theoretically be in 2^n states, perform significantly faster calculations.
Hasan noted that the team’s Materials group, led by Robert Cava, the Russell Wellman Moore Professor of Chemistry and a co-author on the paper, had succeeded in producing the crystal over many months of trial-and-error.
There are still many experimental difficulties ahead, insists Hasan, among them the need for scalability to a large number of Qubits, and getting quantum computing to work in a fault tolerant mode. But he also seems comfortable with the idea that if quantum information is topologically encoded, it can be protected from decoherence and other potential sources of error.
Additional information about Dr. Hasan and his colleagues’ work is available in a recent Princeton University home page article.
A podcast and the presentation are available.

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