Scientists observed a quantum jump in sound in real time by tracking tiny energy changes hundreds of times in milliseconds |
Stanford physicists have recorded what they describe as the first direct observation of quantum jumps of sound in a mechanical resonator. According to the Stanford Report, the team, led by Amir Safavi-Naeini, published its findings in the journal Science on 17 September 2026. Quantum jumps were first demonstrated in trapped ions in 1986 and in photons in 2007. The resonator can vibrate for two milliseconds, and the device took hundreds of readings within that time to pinpoint the moment a phonon moved from an energy state of 1 to 0. The Science abstract reports 85% fidelity for heralded single-phonon states.
How did scientists observe a quantum jump in sound in real time
Quantum jumps have been theorised since the early 1900s. Scientists first demonstrated them in trapped ions in 1986 and later in photons, the fundamental particles of light, in 2007. The report states that observing quantum jumps of sound had remained elusive until the team led by Safavi-Naeini recorded them. It describes the result as completing an arc of scientific exploration that started over a hundred years ago.Stanford Report explains that the smallest possible discrete piece of light is a photon, while a quantum unit of sound, called a phonon, represents the coordinated movement of a large group of atoms. The report notes that, to human senses, the vibration of a struck bell appears to decline gradually rather than stop abruptly. At the quantum level, it says, a resonator’s vibrational energy changes in discrete steps, similar to the quantum behaviour of ions and photons. Earlier experiments had found evidence of these jumps, but the Stanford Report says this study is the first to demonstrate individual phonons making quantum jumps in real time.
Microscopic mechanical resonator helps scientists detect quantum jumps in sound
The mechanical resonator was fabricated using chipmaking techniques. The report says it is so small that many resonators could be packed onto a chip to perform complex functions. It describes the device as working like a microscopic tuning fork that can vibrate for two milliseconds. Stanford Report adds that if a regular-sized tuning fork had the same capability, it would ring for several hours.The length of time the resonator can ring is what made the breakthrough possible. This long “ringdown time” allowed hundreds of readings to be taken to determine the moment the vibration was no longer present and the sound jumped, moving from an energy state of 1 to 0. According to the study published in Science titled ‘Quantum jumps of sound’, the team coupled a lithium niobate mechanical resonator with a superconducting qubit and measured the predicted quantum jumps in phonon number.
How did a superconducting qubit measure phonon energy levels in real time
The researchers had to overcome an ongoing challenge in quantum engineering: how to get a signal out of a quantum system without disturbing its fragile state. Developed a way to pair the microscopic mechanical resonator with a superconducting qubit. The qubit as an electrical circuit that can store quantum information and serve as a detector. Makihara, a recent Stanford doctoral graduate, said the team had to keep developing new processes to make the long-lived vibrating object and integrate it with the qubit without ruining either subsystem.The qubit reads out what is happening in the resonator, checking over and over during the two milliseconds of vibration whether the phonon inside is at an energy level of 1 or 0. This is how the researchers record the moment a quantum jump occurs. The abstract in Science states that quantum mechanics predicts a vibrating object’s energy comes in discrete packets, yet no measurement of its position reveals this. It says that resolving individual energy levels requires a measurement coupled to the resonator’s energy rather than its displacement. The team used a superconducting qubit dispersively coupled to a nanomechanical resonator to perform repeated quantum nondemolition measurements of the phonon number.
Researchers achieve 85% fidelity when creating single-phonon states
An aligned transfer-print technique was used to integrate the qubit and the resonator. The researchers heralded single-phonon states with 85% fidelity and observed quantum jumps between the resonator’s first excited state and ground state. Such behaviour could be of practical use in quantum information processing based on mechanical quantum systems.The ability to detect quantum jumps of sound could help with the error correction problem in quantum computing. In many quantum computing architectures, a quantum jump represents an error, but identifying when these occur has been difficult. The report adds that Safavi-Naeini’s team, working with physicist Michael Roukes’ team at Caltech, is already pursuing use of the platform to detect and identify proteins within cells. Szakiel, a current doctoral student in Safavi-Naeini’s lab, said the work shows “incredibly fine-tuned control of sound”, which the report links to devices such as smartphones.
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