Physicists at Stanford University have, for the first time, directly observed quantum jumps of sound in real-time. The results of the experiment were published in the journal Science. Researchers created a microscopic mechanical resonator that allowed them to see the moment when the system abruptly transitioned from one energy level to another. The scientists worked with phonons – quanta of mechanical vibrations. In the ordinary world, sound fades gradually, but at the quantum level, energy changes in discrete packets.
Quantum jumps were predicted as early as the beginning of the 20th century. In 1986, they were first observed in trapped ions, and in 2007 – in photons. For phonons, previous experiments provided indirect evidence, but individual transitions in real-time had not been recorded until now.
For the experiment, the team developed a resonator using chip technologies, which allowed for a long decay time of vibrations – about 2 ms. During this time frame, the scientists managed to conduct hundreds of measurements and determine when the energy of a phonon transitioned from level 1 to 0. The resonator was connected to a superconducting qubit, which served as a sensor and repeatedly checked the state of the system without destroying it with each measurement. The study's lead researcher, Amir Safavi-Naeini, noted: “We saw that vibrating objects can demonstrate quantum behavior. This is a necessary condition for many operations in quantum computing and sensors.”
One possible application is related to error correction in quantum computers: quantum states are unstable, and the transition of the system between levels in some architectures indicates an error, and to correct it, one must first determine the moment of occurrence. The ability to track such changes in real-time lays the foundation for systems based on mechanical resonators. However, the current experiment is a fundamental work, not a ready-made error correction method.
Another direction is ultra-sensitive sensors. The Stanford team, together with scientists from the California Institute of Technology, is already exploring the possibility of using the resonator and qubit combination to detect and identify proteins inside cells. The authors also consider the application of the technology in electronics: mechanical vibrations are used in smartphones and other devices, and more precise control over them could potentially lead to the creation of new acoustic components.
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