Stanford team observes quantum jumps of sound for first time
Stanford University researchers have directly recorded real-time quantum jumps of sound in a mechanical resonator.
Stanford University physicists have directly observed quantum jumps of sound for the first time. The team watched single phonons, the quantum particles of sound, vanish abruptly from one energy state to another in a microscopic mechanical resonator.
Quantum jumps are sudden transitions between discrete energy levels. They are a foundational concept in quantum theory, first proposed in the early 1900s. Researchers first demonstrated these jumps in trapped ions in 1986 and later in photons in 2007. Observing the phenomenon in sound, however, had remained a significant challenge until now. The findings, led by Stanford physicist Amir Safavi-Naeini, are published in the journal Science.
"What this study shows will allow us to move forward with developing new quantum technologies with sound," said Safavi-Naeini, an associate professor of applied physics. He noted that demonstrating quantum behavior in vibrating objects is a prerequisite for many quantum computing and sensing operations.
Watching Sound Behave Quantum Mechanically
In the macroscopic world, vibrations appear to fade smoothly. A ringing bell grows gradually quieter. At the quantum scale, the behavior is starkly different. Energy changes in distinct steps. The smallest discrete unit of sound is a phonon, which represents the coordinated motion of many atoms. The Stanford experiment directly tracked individual phonons as they made quantum jumps in real time.
A Microscopic Resonator With an Unusually Long Ring
The team built a tiny mechanical resonator using chip fabrication techniques. Its small size means many such devices could potentially be integrated onto a single chip for complex tasks. A critical feature was the resonator's exceptionally long vibration lifetime. It could vibrate, or "ring,"for two milliseconds. If a normal-sized tuning fork had a comparable ability to sustain vibrations, it would continue ringing for several hours."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,said Makihara, a recent Stanford doctoral graduate.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," said Szakiel, a current doctoral student in the lab. The work was supported by Amazon Web Services Inc., the Air Force Office of Scientific Research, the Office of Naval Research, the National Science Foundation, and other agencies.
