Quantum jumps of sound

Amazing stuff! Looks like a clever experiment!

"... Phonons are much larger than photons or electrons, each representing a coordinated group of atoms. Imagine the last note of a piano sonata being held until it naturally fades. While you may hear the sound gradually decline to silence, phonons are actually changing vibrational energy in discrete quantum jumps—like going from a “1 state” (sound) to a “0 state” (no sound). But despite trying for a century, researchers had never been able to observe these jumps.

To make the breakthrough, a team designed a microscopic mechanical resonator that vibrates at a specific frequency when energy is applied, much like a tuning fork. But despite its tiny size, the resonator could vibrate for two milliseconds—a length that, if the resonator were scaled up to the size of a regular tuning fork, would last hours.

As the resonator faded to silence, the team took hundreds of measurements to see when the sound jumped between energy states. To get the readings, they paired the resonator with an electrical detector called a superconducting qubit, which could read out the quantum measurement of the phonon’s energy state (whether it was “0” or “1”). ..."

"In brief: 

• Stanford scientists have confirmed the long-predicted ability of quantum units of sound, or “phonons,” to suddenly change energy levels. 
• The team created a device that takes hundreds of measurements within two milliseconds to pinpoint the moment of a quantum jump.
• The advance has implications for quantum computing and sensing as well as improving everyday technologies, such as smartphones.

..."

From the editor's summary and abstract:

"Editor’s summary

Quantum mechanics predict quantized mechanical energy, but conventional measurements of resonator motion cannot reveal that discreteness. Repeated quantum nondemolition measurements that couple to the discrete energy levels (phonon number) rather than position are required to reveal the quantized jumps in sound. Makihara et al. coupled a lithium niobate mechanical resonator with a superconducting qubit and measured the predicted quantum jumps in phonon number. In addition to the foundational observation, such behavior could be of practical use in quantum information processing based on mechanical quantum systems. ...

Abstract

Quantum mechanics predicts that a vibrating object’s energy comes in discrete packets, yet no measurement of its position reveals this discreteness. Resolving individual energy levels requires a qualitatively different measurement, one coupling to the resonator’s energy rather than its displacement.

We use a superconducting qubit dispersively coupled to a nanomechanical resonator to perform repeated quantum nondemolition measurements of the phonon number. An aligned transfer-print technique integrating the qubit and resonator yields a mechanical lifetime of  milliseconds and a dispersive shift of χπ

 kilohertz per phonon. We heralded single-phonon states with 85% fidelity and observed quantum jumps between the resonator’s first excited state and ground state. These discontinuous transitions are a striking manifestation of quantum mechanics in a massive, vibrating object."

ScienceAdviser

Scientists Catch Sound Making a Quantum Jump With a Microscopic Tuning Fork "Learn how physicists overcame obstacles to watch phonons quantum jump in real-time."

Researchers observe first real-time quantum jump in sound (original news release) "In an experiment, Stanford physicists demonstrated that tiny units of sound can suddenly change energy states, making a quantum jump. This is a long-anticipated breakthrough with the potential to advance a range of technologies."

Quantum jumps of sound

This mechanical resonator, depicted in an illustration (left) and in an image taken by a scanning electron microscope (right), allowed researchers to detect quantum jumps of sound.