Stanford physicists observe quantum jump in sound for first time

A team of Stanford physicists has documented the first direct observation of a quantum jump in sound, capturing the instant a single unit of vibration — known as a phonon — dropped from one energy level to another inside a chip-sized crystal bar. The findings, published in the journal Science, complete a line of inquiry stretching back more than a century and open new paths for quantum computing and sensing.science

A Century-Old Prediction, Finally Confirmed in Sound

Quantum jumps — sudden, discrete transitions between energy states — were first theorized in the early 1900s. Scientists demonstrated them in trapped ions in 1986 and in photons in 2007, but sound had remained out of reach. The Stanford team, led by applied physics associate professor Amir Safavi-Naeini, built a microscopic mechanical resonator from lithium niobate crystal paired with a superconducting qubit that could check the phonon's energy state hundreds of times within a two-millisecond window.humsci.stanford

"What this study shows will allow us to move forward with developing new quantum technologies with sound," Safavi-Naeini said. "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."humsci.stanford

The resonator vibrates for about 2.1 milliseconds — long enough, the team noted, that a regular-sized tuning fork with the same capability would ring for hours. Co-first authors Takuma Makihara and Erik Szakiel developed a fabrication method that places the crystal bar just 75 nanometers above a superconducting circuit, close enough to read the phonon state without destroying it. "We had to continually develop new processes to make this extremely long-lived, vibrating object and then integrate it with the qubit, which is our little electrical detector — without ruining either subsystem," Makihara said.earth+1

From Observation to Error Correction

The practical stakes are immediate. In many quantum computing architectures, a quantum jump represents an error — information leaking away mid-calculation. Detecting when such errors occur has been a persistent obstacle for the field. The Stanford device not only spots the loss but leaves the remaining quantum state intact, a prerequisite for real-time error correction.earth+1

The team is already applying the platform beyond computing. In collaboration with physicist Michael Roukes's group at Caltech, the researchers are using the resonator to try to detect and identify proteins within cells. "This shows we can have incredibly fine-tuned control of sound, which might mean that devices that use sound as a fundamental technology can get much better," Szakiel said.humsci.stanford

Next, the lab plans to build a device with two resonator bars on a shared qubit, where losing a phonon from either bar would register as a flagged error rather than a silent corruption — a step closer to the architecture error correction demands.earth