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OnCampus Weekly...MAY 6/05

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OnCampus Weekly



the quantum mechanics edition

By Garth Boucher

T he “Age of Information” is about to get an extreme makeover.

The makeover is coming at the hands of physicists, mathematicians and computer scientists who, for the first time, are successfully harnessing the mind bending principles of quantum mechanics to encode and process information.

lvovskyCurrently, we encode our information classically — that is, using physical systems subject to Sir Isaac Newton’s time-honoured laws of physics where particles collide in predictable, calculable ways. The basic unit of information currency in this realm is the bit which represents one of two states – on or off, 1 or 0. The bit is physically realized in a variety of ways, including magnetic regions on disks, voltages in circuitry, pits on compact disks or even pencil marks on paper.

The challenge is to bridge the gaping chasm that separates Newton’s classical physics and the world of quantum mechanics where particles can be in two places at the same time.

Enter U of C physics professor Alexander Lvovsky.

Lvovsky leads the Quantum Information Technologies group (QIT), which is part of U of C’s recently launched Institute for Quantum Information Science.

His team is investigating the possibility of using single portions or “quanta” of light — photons — as a means of carrying information. The first hurdle in this process is immediate.

“ It’s not easy to generate just one photon” says Lvovsky. “It’s only recently that we’ve learned how to do this in a controlled manner.”

The photons are created with distinct polarizations — “vertical” and “horizontal,” corresponding with the two states of a classical bit — 1 and 0.

But it is here that the counterintuitive quantum world imposes its bewildering and bizarre will. Photons can in fact be in two different states at the same time, effectively attaining a superposition of the “1 or 0” state. It is something we have no analogy for in our macroscopic world of everyday experience.

Understanding and manipulating quantum superpositions is one of the keys in making the transition from classical to quantum information technology. Initially considered a confusing impediment, quantum phenomena is something researchers like Lvovsky are steadily coming to terms with in a practical sense. They now realize that this unique quantum capability has the potential to significantly increase the amount of information that can be carried. The quantum bits of information have naturally been dubbed “qubits”.

Qubits are of little practical interest however, unless they can be reliably stored and retrieved. This problem forms the second axis of research pursued by Lvovsky and his team.

“ All computers, quantum or classical, require memory” explains Lvovsky. “But this is problematic for photons — they are so tiny and so fast that there aren’t many materials that they will interact with.”

One possibility the QIT team is investigating is the use of elemental rubidium vapor as a kind of receptacle into which an injected photon might transfer or “store” its quantum state. This is proving to be an extremely delicate and technically demanding process as the photons generated need to have precisely the right properties or they will effectively “miss” the rubidium atoms.

If the details of Lvovsky’s research seem abstract and difficult to grasp, his vision of the importance of his team’s research is at once exciting and sobering.

“ The impact of quantum information technology ranges from revolutionizing drug research to making the cryptographic codes used to protect today’s most sensitive information obsolete and easy to crack.”

Lvovsky cites credit card purchases over the Internet as an example of a type of transaction for which security could no longer be guaranteed with the availability of quantum computers.

“ An individual with such technology could totally disrupt the world’s banking and other security systems. For this reason, governments are in a hurry to fund this research.”