Sound of an atom



photo credit: Philip Krantz, Krantz NanoArt. An artificial atom (right) generates sound waves consisting of a stream of quantum particles picked up on the left by a "microphone" of metal fingers.

It’s been only a day since an “artificial atom” was used to do extraordinary things with light, but now it’s the turn of sound. In a new paper published in Sciencelead author Martin Gustafasson describes how an artificial atom and “the weakest sound that can be detected” form a tool for studying quantum behavior.
An artificial atom is a material made to behave electronically like a single atom. They can be formed from millions of billions of atoms, but share the atomic trait that they absorb certain quantities of energy and may then release this energy as light.

In a preparatory paper published in a July issue of Physical Review A, a sub-group of theScience authors note that an important feature of atoms is that they are much smaller than the wavelength of optical light, making them appear like a point. To achieve the same effect with formations made from multiple atoms, it is necessary to use the longer wavelengths of microwave radiation.

The authors considered the possibility of using sound waves instead of the electromagnetic spectrum and discussed what would be expected if these were coupled to artificial atoms.

Less than two months later, their theory has become a reality with a superconducting artificial atom 0.01mm long coupled to phonons, or “quanta of vibrations"—the smallest possible units of sound waves. “Our results highlight the similarities between phonons and photons but also point to new opportunities arising from the unique features of quantum mechanical sound,” the authors write.

“Due to the slow speed of sound, we will have time to control the quantum particles while they travel," says Gustafsson of Sweden's Chalmers University of Technology. "This is difficult to achieve with light, which moves 100,000 times more quickly." 

Co-author Per Delsing claims, “We have opened a new door into the quantum world by talking and listening to atoms.” However, if the idea of conversing with the building blocks of matter appeals to you, you'll need a squeaky voice; the team used a frequency of 4.8GHz, 20 octaves above the highest note on a piano.

The team hope they can use this new information to learn how to control quantum behavior better, including the quest for electrical circuits—and therefore computers—that operate on quantum principles.

“The low propagation speed of phonons should enable new dynamic schemes for processing quantum information, the authors conclude, “and the short wavelength allows regimes of atomic physics to be explored that cannot be reached in photonic systems.”

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