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News

Researchers successfully construct artificial atom which lead to faster, more advanced quantum computers

Yale University : 16 May, 2002  (New Product)
Using a microscopic grain of superconducting aluminum, a researcher who is now at Yale and his colleagues at CEA-Saclay Laboratories in France, have constructed an 'artificial atom' that can be used as a quantum bit, an essential component for the construction of a quantum computer.
Quantum computers can solve certain problems far faster than ordinary computers.

'This brings us one step closer to building a quantum processor,' said principal investigator Michel Devoret, formerly director of the Quantronics group at CEA-Saclay and now professor of applied physics and physics at Yale.

Published in the May 3 issue of Science, the article reports on two breakthroughs. First, an electrical circuit the team constructed employs a new design that strongly isolates the artificial atom from its environment so that it retains its quantum coherence-the essential feature that distinguishes its behavior from a classical system-more than 100 times longer than in previous similar systems. Second, the researchers invented a new method for reading out the quantum state of the circuit with unprecedented efficiency and accuracy.

An essential feature of quantum mechanics is that the act of measurement changes the state of the system being observed. Ordinarily, a large object containing many atoms obeys the laws of classical mechanics and does not behave quantum mechanically. This is because interactions with other atoms nearby in the environment effectively cause the system to be continually under observation.

Devoret and his colleagues developed a new design with an operating point at which it is very difficult for the environment to distinguish between the two quantum states of the circuit. At this 'sweet spot,' the system can maintain its wave-like quantum coherence for more than 10,000 oscillations of the wave (about 0.5 microseconds). It has been speculated that 10,000 oscillations is the minimum degree of coherence at which quantum error correction techniques begin to become feasible. In principle, these techniques could allow quantum coherence to be extended for much longer periods.

Even though the grain of superconducting aluminum contains about one billion atoms, the superconductivity causes all the electrons in the grain to act coherently and in concert so that the circuit has only two distinct quantum energy states. In these two states, the electrical current in the wires attached to the 'atom' flows in opposite direction.

'Remarkably, quantum mechanics permits the possibility that the circuit is in both states at the same time,' said Devoret. 'This means that we are uncertain which way the current is flowing until we measure it. We were able to successfully demonstrate complete quantum control of the state of the system using pulses of microwaves to place the circuit into such states, and, for the first time in a solid-state quantum bit, demonstrated a particular kind of quantum mechanical wave interference phenomenon known as Ramsey fringes.'

The work was performed in the Quantronics Group in Saclay, France. Other authors on the study include Denis Vion, Abdelhanin Aassime, Audrey Cottet, Philippe Joyez, Hugues Pothier, Cristian Urbina, and Daniel Esteve.
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