The short version
- Vibration, like light, comes in tiny indivisible packets called phonons, and a Stanford team has now watched one disappear in real time.
- They did it by making a crystal resonator that keeps ringing for about 2 milliseconds, far longer than earlier versions.
- Quantum jumps were seen in atoms in 1986 and in light in 2007, and sound was the holdout.
Quantum physics says a vibrating object’s energy comes in fixed steps, but as the team’s paper puts it, “no measurement of its position reveals this discreteness.” Physicists at Stanford, led by Amir Safavi-Naeini, have now seen those steps directly. In a paper published in Science on September 17, they report watching a microscopic resonator drop from one phonon, a single quantum of the same kind of vibration that carries sound, to none.
The resonator, a sliver of thin-film lithium niobate made with chip-fabrication methods, keeps vibrating for about 2 milliseconds. A superconducting qubit measured it again and again in that window and caught the instant the energy left, a “quantum jump.” The paper reports 85% fidelity for the single-phonon state. Getting there meant stretching the resonator’s lifetime by four to five orders of magnitude, mostly by cleaning up surface defects. “There were probably three generations of students” on that part alone, Safavi-Naeini told Physics World, which revisited the result this week.
Quantum jumps were first seen in trapped ions in 1986 and in light in 2007. The team names sound-based quantum error correction and very sensitive force and mass sensors as next uses. The vibrations here live inside a chip, far from anything an ear could hear.
