Stanford researchers have directly observed quantum jumps of sound in a mechanical resonator for the first time, marking the latest milestone in a line of quantum physics research that stretches back more than a century. Quantum jumps -- sudden transitions from one energy state to another -- have been part of quantum theory since the early 1900s. Researchers first demonstrated them in trapped ions in 1986, followed by photons, the fundamental particles of light, in 2007.
Sound, however, remained a more difficult target. A team led by Stanford physicist Amir Safavi-Naeini has now recorded these jumps directly, with the findings published in Science. "What this study shows will allow us to move forward with developing new quantum technologies with sound," said Safavi-Naeini, associate professor of applied physics in the Stanford School of Humanities and Sciences.
"We have seen that vibrating objects can exhibit quantum behavior, which is the prerequisite for many of the operations needed by quantum computing and sensing." Watching Sound Behave Quantum Mechanically The smallest discrete unit of light is a photon. The quantum equivalent for sound is a phonon, which represents the coordinated motion of many atoms. In everyday life, vibration seems to fade smoothly.
A ringing bell, for example, gradually grows quieter until the sound disappears. At the quantum scale, the picture is very different. A resonator's vibrational energy changes in distinct steps rather than continuously, much like the behavior previously observed in ions and photons.
Earlier experiments had produced evidence that sound could undergo these transitions. The new study goes further by directly tracking individual phonons as they make quantum jumps in real time. A Microscopic Resonator With an Unusually Long Ring The mechanical resonator used in the experiment was built with chip fabrication techniques.
Its tiny size means that many such resonators could potentially be placed on a single chip to carry out complicated tasks. A critical feature was how long the device could continue vibrating. Acting somewhat like a microscopic tuning fork, the resonator can vibrate for two milliseconds.
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