Researchers at Stanford University have, for the first time, directly observed in real-time a quantum transition in a system of mechanical oscillations. The results of the experiment were published in the journal Science. The scientists studied phonons—quanta of mechanical oscillations that change energy at the quantum level not continuously, but in discrete amounts. During the study, physicists recorded the moment when the system transitioned from one energy level to another. Similar jumps had previously been observed in other quantum objects: trapped ions—as early as 1986, and photons—in 2007. For phonons, there had only been indirect evidence of such transitions.
For the experiment, the team created a microscopic mechanical resonator, functioning similarly to a small tuning fork. The device was created using technologies employed in the production of electronic chips. An important parameter was the prolonged damping time of oscillations—about 2 ms. Within this interval, scientists could conduct hundreds of measurements and determine the moment of energy transition of a phonon from the first level to the ground level. To register the state, the resonator was linked with a superconducting qubit. It served as a sensor and allowed for multiple checks of the system without destroying its state after each measurement. This approach enabled not only the detection of transitions but also tracking them directly over time.
Researchers primarily view the experiment as fundamental work, but the method developed could have several applications. One of them is related to quantum computers, where state instability leads to errors: correction requires identifying the moment of an unwanted transition. Real-time observation of phonons lays the foundation for such systems, although the work does not yet offer a ready error correction mechanism. Another possibility is ultra-sensitive sensors. The Stanford team, in collaboration with scientists from the California Institute of Technology, is exploring the potential use of the resonator-qubit link to detect proteins within cells. Additionally, the technology could potentially be applied in electronics, where mechanical oscillations are already used in smartphones and other devices.
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