Scientists have figured out how to interact with an artificial atom using sound. While other teams have connected tiny membranes or strings to atoms, this is the first time they’ve connected a sound wave to an atom.
The experiment may seem unusual, but the result could lead to the long-term goal of building quantum computers that can harness the power of sound to make electrical circuits and faster data processors.
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The team started by first making an artificial atom. Next, they charged it with energy. Normally, atoms release energy in the form of light, called a photon. However, in this experiment, the atom was designed to both emit and absorb energy in the form of sound, called a phonon.
“When we make artificial atoms, we can tailor them to our purposes,” Gustafsson said. “We designed them so they will couple to acoustic waves on the surface of a microchip. We also have a little structure that works as both a loudspeaker and a microphone. So we can send a soundwave from the loudspeaker, reflect against the atom, come back to the same microphone/loudspeaker and use it to communicate with the atom.”
The emitted sound was, in theory, a stream of quantum particles, the weakest whisper physically possible. In fact, it was about the same frequency of radio waves of a mobile phone or wireless network.
“It’s a D-note, but 20 octaves higher than highest note on grand piano,” said Martin Gustafsson, a post-doctoral researcher at Columbia University and lead author on the study. “It’s much too high pitched for anyone to hear.”
“We are bouncing energy off the atom,” Gustafsson said. “What’s new is that its sound bouncing off the atom instead of light. It’s a new type of interaction.”
The experiments were done at Sweden’s Chalmers University of Technology while Gustafsson was a post-doc there. The results are published online today in the journal Science Express.
In this experiment, the artificial atom becomes a superconducting circuit that can be used as a qubit, which is the name for the building block of a quantum computer.
Since sound moves 100,000 times more slowly than light, scientists have more time to control sound particles, or phonons, while they travel, according to Gustafsson. The researchers cooled their experiments to near absolute zero, or 20 millikelvin, to make sure any heat energy would not disturb the atom.
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Steve Rolston, co-director of the University of Maryland’s Joint Quantum Institute, says the work is an interesting step toward using sound energy in quantum computing.
“Whether it has implications for quantum computing may be too early to tell, but it expands the toolbox for technologies to work with,” Rolston said.
Using slow-moving sound to carry information for such a computer may be a good idea, he added.
“Normally slow is bad, but if it’s slow enough you could switch something while (the phonon particle) is propagating. It gives you more possibilities.”