Stanford University physicists have recorded the first direct observation of quantum jumps of sound in a mechanical resonator, capturing individual phonons making sudden energy-state transitions in real time. The breakthrough, published in the journal Science, bridges a century of scientific theory and offers a new pathway toward quantum computing error correction.
A Century of Theory Meets Real-Time Observation
Quantum jumps—sudden transitions from one energy state to another—have been theorized since the early 1900s, according to reporting by Phys.org. While scientists first demonstrated these discrete jumps in trapped ions in 1986 and later in photons in 2007, observing the phenomenon in sound had remained elusive until now.
A research team led by Stanford physicist Amir Safavi-Naeini has finally recorded quantum jumps of sound, documenting their findings in the journal Science. At the quantum level, a mechanical resonator’s vibrational energy changes in discrete steps rather than declining gradually like a struck bell. Although earlier experiments found evidence of these jumps, the Stanford study marks the first time individual phonons have been observed making quantum jumps in real time.
Engineering the Microscopic Tuning Fork
To capture the phenomenon, the researchers built a mechanical resonator using chipmaking techniques. Small enough to be viewed with a microscope, the device functions like a microscopic tuning fork. Its physical size makes it a strong candidate for packing numerous resonators onto a single chip to execute complex functions.
The critical factor enabling the breakthrough is the resonator’s exceptionally long resonance, or ringdown, time. The device can vibrate for two milliseconds—a duration that, scaled to a regular-sized tuning fork, would equate to ringing for several hours. This prolonged ringdown allowed researchers to take hundreds of readings to spot the exact moment vibrational energy jumped from an energy state of 1 to 0.
Pairing Resonators with Superconducting Qubits
Extracting a signal from a quantum system without disrupting its fragile state has long challenged quantum engineers. To solve this, co-first authors Takuma Makihara and Erik Szakiel paired the microscopic mechanical resonator with a superconducting qubit—an electrical circuit capable of storing quantum information and acting as a detector.
We had to continually develop new processes to make this extremely long-lived, vibrating object and then integrate it with the qubit, which is our little electrical detector—without ruining either subsystem.
Takuma Makihara, recent Stanford doctoral graduate
The qubit repeatedly checks the mechanical resonator during its two-millisecond vibration to determine whether the phonon is in an energy state of 1 or 0, enabling the team to record the jump as it happens.
Implications for Quantum Computing and Cellular Sensing
This foundational advance addresses a major hurdle in quantum computing. Fragile quantum states often trigger errors before calculations finish, and quantum jumps frequently represent those errors. Detecting when these jumps occur is a vital step toward solving the quantum error-correction problem.
Beyond computing, the high sensitivity and small size of the resonator-qubit combination open doors for precise sensing applications. Safavi-Naeini’s team is already collaborating with physicist Michael Roukes and researchers at Caltech to utilize the platform for detecting and identifying proteins within cells.
This shows we can have incredibly fine-tuned control of sound, which might mean that devices that use sound as a fundamental technology can get much better.
Erik Szakiel, current doctoral student in Safavi-Naeini’s lab