With First Mechanical Qubit, Quantum Computing Goes Steampunk

An anonymous reader quotes a report from Science Magazine: Qubits, the strange devices at the heart of a quantum computer that can be set to 0, 1, or both at once, could hardly be more different from the mechanical clockwork used in the earliest computers. Today, most quantum computers rely on qubits made out of tiny circuits of superconducting metal, individual ions, photons, or other things. But now, physicists have made a working qubit from a tiny, moving machine, an advance that echoes back to the early 20th century when the first computers employed mechanical switches. 'For many years, people were thinking it would be impossible to make a qubit from a mechanical system,' says Adrian Bachtold, a condensed matter physicist at the Institute of Photonic Sciences who was not involved in the work, published today in Science. Stephan Durr, a quantum physicist at the Max Planck Institute for Quantum Optics, says the result 'puts a new system on the map,' which could be used in other experiments—and perhaps to probe the interface of quantum mechanics and gravity.

The new mechanical qubit is unlikely to run more mature competition off the field any time soon. Its fidelity -- a measure of how well experimenters can set the state they desire -- is just 60%, compared with greater than 99% for the best qubits. For that reason, 'it's an advance in principle,' Bachtold says. But Durr notes that a mechanical qubit might serve as a supersensitive probe of forces, such as gravity, that don't affect other qubits. And ETHZ researchers hope to take their demonstration a step further by using two mechanical qubits to perform simple logical operations. 'That's what Igor is working on now,' [says Yiwen Chu, a physicist at ETH Zurich]. If they succeed, the physical switches of the very first computers will have made a tiny comeback.

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