A team of researchers from Stanford University has made a groundbreaking observation in quantum science by directly detecting quantum jumps in sound within a mechanical resonator. This achievement, detailed in the journal Science, marks the first time such quantum jumps—sudden changes in energy levels—have been seen in sound waves. Previously, these jumps had only been observed in systems like trapped ions and photons. The study was led by Amir Safavi-Naeini, an associate professor of applied physics at Stanford. Quantum jumps in sound involve the movement of atoms, represented as phonons, which are the quantum particles of sound. Although sound vibrations seem to fade gradually to human ears, at the quantum level, these transitions occur in discrete, step-like changes. While earlier experiments hinted at the existence of these jumps, this study is the first to observe individual phonons undergoing these quantum transitions in real time. The experiment used a specially designed mechanical resonator, which is tiny and can be manufactured using techniques similar to those used in chipmaking. This resonator can "ring" for two milliseconds—far longer than a standard tuning fork, which rings for only a fraction of a second. This longer ringing time allowed the researchers to take multiple readings and detect the precise moment when vibrational energy transitioned from one energy state to another. To observe these quantum jumps, the team combined the mechanical resonator with a superconducting qubit, an electrical circuit capable of storing and detecting quantum information. This integration allowed the researchers to repeatedly monitor the resonator’s vibrational state during its two-millisecond vibration period, identifying the exact moment a quantum jump took place. The ability to detect quantum jumps in sound could have important implications for quantum computing, especially in error correction. Quantum computers rely on maintaining delicate quantum states, and being able to detect when these states change is essential for identifying and correcting errors. Additionally, the combination of a mechanical resonator and a qubit could be used in highly sensitive sensing technologies, such as detecting proteins inside cells. The researchers, including co-first authors Takuma Makihara and Erik Szakiel, emphasized the need to develop new methods to integrate the resonator and qubit without disrupting either system. Their findings may also lead to improvements in everyday technologies that rely on sound, such as smartphones.