摘要：A simple mechanical system built from aluminium rods uses vibrations to encode information, mimicking quantum computing in a non-quantum system

Some properties of quantum computers can be imitated with sound trapped in a simple mechanical device. This has the advantage of being less fragile than quantum computers, while still replicating some of their properties.

Quantum computers could eventually solve problems that are impossible for best conventional supercomputers, but they are tricky to work with. Many lose their quantumness, which is key for their advantages over ordinary computers, and stop working very quickly because of disturbances from their environments – and some must be isolated in cryogenic fridges to work at all.

Pierre Deymier at the University of Arizona and his colleagues glued together three aluminium rods, each a little over half a metre long, to create something that could act like a quantum bit, or a qubit, but with a much larger device. Qubits differ from conventional bits because in addition to encoding information as 1s and 0s, they also have many so-called superpositions that are both and neither at once.

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The researchers used speakers to create vibrations at one end of the stack, and detected them at the other. When the sound frequencies were tuned just right, localised “chunks” of sound formed in the rods – the researchers named them “phi-bits”. Deymier says that information could be input into the phi-bits by tuning the sound. Because many phi-bits existed simultaneously, but were not independent from each other, he says they could also be forced into a superposition, or a mixture of all their individual states.

The team devised ways of implementing simple computations, like analogues of changing a 1 to a 0. They also made more complicated, quantum-like states that share some properties with  entangled particles in quantum systems, such as not being able to separate a single phi-bit from others. In all experiments the device was “frighteningly simple,” says Deymier.

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“We have a lot of flexibility in what we can do here. And it is such a new system that we have not yet discovered its limits,” he says. His team presented the work at a meeting of the Acoustical Society of America in Chicago, Illinois, on 12 May.

However, the limits on how much a non-quantum system can imitate a quantum system – and therefore reap advantages of quantumness – may be a matter of fundamental physics, says Gerd Leuchs at the University Erlangen-Nuremberg in Germany. Because quantum objects have wave-like properties, some of what they do, such as forming superpositions, can be replicated with other waves like sounds, he says.

But quantum objects also have ways of responding to interactions that are fully unique. “Such quantum behaviour may be necessary to get all the advantages of quantum computing, and we don’t know of any non-quantum equivalent,” says Leuchs.