Stanford physicists have recorded the first direct, real-time observation of quantum jumps in phonons, the quantum units of sound, completing a scientific arc that began over a century ago.
Quantum jumps, sudden transitions between discrete energy states, were first seen in trapped ions in 1986 and in photons in 2007, but capturing them in mechanical sound had remained elusive. The team, led by Amir Safavi-Naeini, fabricated a chip-scale mechanical resonator so finely engineered that it rings for two milliseconds (equivalent to a macroscopic tuning fork ringing for hours), allowing hundreds of measurements to pinpoint the exact moment a phonon jumps from energy state 1 to 0.
The result, published in Science, proves that macroscopic vibrating objects exhibit quantum behavior, a prerequisite for phonon-based quantum computing and next-generation sensing technologies. "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. The resonators are small enough to pack by the thousands onto a single chip, bringing sound-based quantum circuits closer to practical deployment in everyday devices, from smartphones to quantum sensors.