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Quantum information now readable

April 08, 2002

Chalmers researchers in Sweden, in an EU project involving colleagues from France, Holland, Germany, Italy and Finland, have shown that outdata from superconductor quantum computers can be read directly, even though the signal consists only of the presence or absence of two electrons, a so-called Cooper pair.

How far away are we from a functional quantum computer? Research results on quantum computers are beginning to appear. Göran Johansson at the Department of Microelectronics and Nanoscience reports that the Chalmers research team he is a member of has been able to produce readouts of superconductor quantum computers. The key to success lies in being able to meter tiny charges before they move on.

Different research teams are studying different problems involving quantum computers. Research is pursuing many paths at the same time. "But even very simple quantum computers are still at least ten years down the road," says Göran.

The Chalmers research team, led by Per Delsing, are already the best in the world, together with their colleagues at Yale, when it comes to the rapid metering of charges with the aid of so-called monoelectron transistors. Working with theoreticians from their Chalmers colleague Göran Wendin's team, they have now shown that it is possible to register a quantum bit rapidly enough to retrieve the information before it is destroyed by the metering itself.

Delsing's and Wendin's research teams are part of an EU consortium, SQUBIT, coordinated by Chalmers University of Technology in Sweden. It comprises seven world-class European laboratories and is the world leader, ahead of the U.S. and Japan, for example. The French node at CEA, Saclay, has just presented a superconductor circuit representing a quantum bit with an extremely long lifetime, a world record for this type, and has tremendous potential to expand this into a small basic quantum computer with 5-10 quantum bits within ten years.

"Chalmers has just applied for EU funding to extend our collaboration and to actually build an elementary quantum computer. What's more, we plan to take part in an even bigger effort within the EU's seventh framework program in quantum informatics, quantum computers, and nanotechnology," adds Göran Wendin.

Quantum computers are a new type of computers based on the laws of physics at the atomic level, so-called quantum physics. The principle is the same as that of Schrödinger's famous cat, which is both dead and alive until you open the lid and check. The bits in a quantum computer are both zero and one, until you read them.

In 1995 a scientist at IBM proved that a quantum computer can factor large numbers into prime numbers exponentially faster than a conventional computer. Since the security of many encryption systems relies on this factoring taking a long time, a functional quantum computer would be able to crack today's codes in a short period of time. Other more peaceful applications of a quantum computer would be to efficiently simulate large molecules, which would be a great boon to the drug industry.

The difficulty in constructing a quantum computer lies in shielding the bits so that nothing in their environmentan unwanted electron that is oscillating a little too much, for example'looks' at them and thus forces them to decide whether they are zeros or ones. This is why these experiments are carried out at extremely low temperatures and using superconductive materials.

VetenskapsrÃ�det (The Swedish Research Council)

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