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Scientists at Stanford University have directly observed individual quantum jumps in sound, providing the clearest demonstration yet that mechanical vibrations can transition between discrete quantum energy states.
The experiment tracked a microscopic mechanical resonator as its vibrational energy changed between quantum states. The achievement extends a phenomenon first explored in the early days of quantum mechanics and could open new possibilities for quantum computing, sensing, and technologies that rely on precisely controlled sound.
Quantum jumps are sudden transitions between discrete energy states. Researchers first demonstrated them experimentally in trapped ions in 1986 and later observed similar behavior in photons, the fundamental particles of light. Sound presents a more complicated challenge because its quantum counterpart, the phonon, represents coordinated vibrations involving many atoms.
In everyday life, vibrations appear to change continuously. A ringing bell gradually becomes quieter, for example. At the quantum level, however, vibrational energy can change in discrete steps. The Stanford team, led by physicist Amir Safavi-Naeini, was able to observe those transitions directly rather than simply measuring their effects.
The researchers built a tiny mechanical resonator using chip fabrication techniques. The device behaves like a microscopic tuning fork and can continue vibrating for about two milliseconds. While that may seem brief, it is exceptionally long for a microscopic quantum system. The extended vibration time gave the researchers enough opportunity to perform hundreds of measurements.
A superconducting qubit was used as a quantum detector. Developed through work by co-first authors Takuma Makihara and Erik Szakiel, the system repeatedly checked the resonator without destroying its fragile quantum state. By monitoring whether the resonator contained one phonon or none, the researchers could identify the moment when it made the transition from the energy state 1 to 0.
Safavi-Naeini said the result demonstrates that vibrating objects can display quantum behavior, a prerequisite for several operations needed in quantum computing and sensing.
The technique could eventually help researchers detect quantum errors, since unwanted transitions can indicate that a quantum computation has been disrupted. The resonator-qubit system may also have applications in highly sensitive measurements, with the team exploring whether it could help detect proteins inside cells.
The researchers also believe precise control of mechanical vibrations could improve technologies that already rely on sound, potentially extending the impact of quantum acoustic research beyond specialized laboratory systems.
