Stanford team observes first real-time quantum jump in sound

A Stanford team has directly observed individual phonons, the smallest units of vibrational energy, making real-time quantum jumps in a nanomechanical resonator. Led by physicist Amir Safavi-Naeini, the experiment tracked a mechanical system as it transitioned from an occupied vibrational state to an empty one. The findings, published in Science as “Quantum jumps of sound,” provide the first real-time demonstration that individual quanta of sound can make an abrupt, measurable transition. The result completes a scientific progression that began with quantum jumps being theorized in the early 1900s, followed by experimental observations in trapped ions in 1986 and photons in 2007.

Quantum jumps are sudden changes between discrete energy states, rather than the gradual fading normally associated with the vibration of a struck bell. A quantum of sound, called a phonon, differs from a photon in one important respect: rather than representing the smallest piece of a light field, it describes the coordinated movement of many atoms. Earlier experiments had provided evidence of discrete changes in mechanical energy, but the Stanford study is the first to demonstrate individual phonons making quantum jumps while they were being monitored in real time. The team recorded the moment when a resonator’s vibrational energy changed from state 1 to state 0, effectively catching the disappearance of its final phonon as a distinct event.

To make that transition observable, the researchers fabricated a mechanical resonator using techniques common to chipmaking. The structure is small enough that many such resonators could be packed onto a single chip to perform more complex functions. It behaves like a microscopic tuning fork, but its most important experimental property is how long it continues to vibrate after being excited. The resonator has a ringdown time of about two milliseconds. By comparison, the Stanford researchers said, a regular-sized tuning fork with the same capability would ring for several hours. This extended persistence provided a practical window for making repeated measurements of the resonator’s quantum state.

The experiment depended on collecting hundreds of readings during those two milliseconds of vibration. Each reading established whether a phonon was present, corresponding to an energy level of 1, or absent, corresponding to an energy level of 0. By repeatedly interrogating the resonator and determining the precise point at which the vibration was no longer present, the researchers resolved the transition from one state to the other. The study therefore did more than show that mechanical vibrations have discrete energy levels: it established when an individual quantum jump occurred during the system’s ongoing decay. That timing represents the central advance behind the team’s description of the result as a real-time observation of a quantum jump of sound.

A major engineering challenge was reading information from the resonator without disturbing the delicate quantum state being measured. Co-first authors Takuma Makihara and Erik Szakiel addressed that problem by coupling the microscopic mechanical resonator to a superconducting qubit, an electrical circuit that can store quantum information and serve as a detector. The qubit repeatedly checked the mechanical system during its two-millisecond ringdown to determine whether the phonon occupied energy level 1 or had disappeared to level 0. This sequence of readout operations provided the temporal resolution required to identify the jump, while linking a mechanical degree of freedom to an electronic quantum device capable of performing repeated measurements.

Integrating the two components also required the researchers to develop fabrication processes that preserved the performance of both subsystems. Makihara, a recent Stanford doctoral graduate, said the team continually refined methods for making the extremely long-lived vibrating object and integrating it with the qubit “without ruining either subsystem.” The resulting hybrid platform allowed a quantum circuit to interrogate a mechanical quantum state without prematurely terminating the resonator’s vibration. Beyond providing evidence for single-phonon transitions, the experiment demonstrates a working readout method for repeatedly monitoring a mechanical quantum state and determining when one quantum of energy is lost.

Safavi-Naeini, an associate professor of applied physics in Stanford’s School of Humanities and Sciences, said the study provides a foundation for developing new quantum technologies with sound. “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,” he said. The finding shows that a chip-fabricated mechanical structure can support, preserve and reveal single-phonon transitions. It also establishes a platform in which mechanical and electronic quantum systems can be coupled closely enough for one to serve as a detector for the other, an approach that may support further research on sound as a controlled carrier of quantum information.

One prospective use is improving error correction in quantum computing. In many quantum-computing architectures, a quantum jump represents an error, while identifying exactly when such a jump occurs has been difficult. Detecting discrete transitions in mechanical energy could therefore offer another means of tracking errors in systems where they occur. The experiment did not solve the broader quantum error-correction problem and did not demonstrate a complete error-correcting protocol. Instead, it showed that individual mechanical energy losses can be detected and timed, giving researchers a specific measurement capability that the team describes as a foundational first step toward error correction and other sound-based quantum technologies.

The small size and high sensitivity of the resonator-and-qubit combination also make it a candidate for precision sensing. Safavi-Naeini’s group is already working with physicist Michael Roukes’ group at the California Institute of Technology on using the platform to detect and identify proteins within cells. That application is an ongoing objective rather than an outcome established in this experiment. The technology could also contribute to more capable sound-based devices. Szakiel, a doctoral student in Safavi-Naeini’s laboratory, said the level of control demonstrated might improve devices in which sound is fundamental, including smartphones and other everyday technologies. These possibilities build on the measured single-phonon behavior rather than representing tested consumer applications or demonstrated clinical benefits.

The study brings a century-long line of inquiry to a distinct experimental endpoint. Stanford researchers showed that the energy of a vibrating mechanical structure can be read in discrete units, that an individual phonon can be followed as it moves from the occupied state to the empty state, and that the transition can be timed through repeated measurements by a superconducting qubit. The work was published in Science on September 17, 2026, under the title “Quantum jumps of sound,” with the canonical DOI 10.1126/science.aeh7535. Additional Stanford contributors included David Schuster, Shannon Harvey, Mihir Pendharkar, Rachel Gruenke-Freudenstein, Oliver Hitchcock, Matthew Maksymowych and Kaveh Pezeshki. The achievement does not change ordinary acoustics, but it makes an elusive transition in mechanical sound directly observable and supplies a practical platform for continued work in quantum computing, quantum sensing and hybrid mechanical-electronic devices.

Subject of Research: Real-time observation of single-phonon quantum jumps in a nanomechanical resonator

Article Title: Researchers observe first real-time quantum jump in sound

Article References: Researchers observe first real-time quantum jump in sound. Original publication (Bibliographic details unavailable.)

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Keywords: quantum acoustics, phonons, quantum jumps, mechanical resonators, superconducting qubits, quantum computing, quantum sensing, nanomechanics, Stanford University, Science, Researchers, observe