Stanford University researchers make first real-time measurement of quantum jumps in sound

Researchers at Stanford University have made the first real-time measurement of quantum jumps in sound, an achievement that opens new directions for scientific exploration and could have immediate applications in quantum computing and sensing. A quantum jump is a sudden transition between energy states in a quantum system. The concept of quantum jumps has existed for more than a century; theoretical physicist Niels Bohr first proposed the idea in 1913. It was not until 1986 that scientists first observed quantum jumps in trapped ions, followed in 2007 by observations of quantum jumps in photons, the fundamental particles of light.

First observation of quantum jumps in sound

Nearly two decades later, a team of scientists led by Stanford physicist Amir Safavi-Naeini observed quantum jumps in phonons, the fundamental units of sound. To explain their discovery, Safavi-Naeini offered the example of a struck bell, whose sound gradually fades over time rather than vanishing all at once. At the quantum scale, however, those diminutions occur as discrete jumps, which Safavi-Naeini's team measured in real time, an unprecedented feat. How did they do it? To carry out the measurement, the researchers built a mechanical resonator comparable in size to a computer chip.

The resonator's small size allows multiple units to be placed on a single chip. Like a tuning fork, the resonator rings out when struck, but the version designed by the researchers has a "ringing" time of just two milliseconds. Though that sounds tiny, at the microscopic scale at which the resonator operates, it is the equivalent of a tuning fork vibrating for hours. The resonator's long ringing time, or "decay time," therefore allows the researchers to take hundreds of readings and accurately mark the moments at which its vibrations transition from 1 to 0, or undergo a quantum jump.

Challenges and solutions

Challenges and solutions One of the main challenges in studying quantum systems is extracting a signal without disturbing their fragile states. The Stanford team found a way to pair the resonator with a superconducting qubit so that it could serve as a detector. The paired qubit enabled the researchers to detect in real time the exact moment a quantum jump occurred. Beyond enabling real-time detection of quantum jumps, the research lays the groundwork for many future quantum advances. In quantum computing, for example, fragile quantum states can cause errors to appear before a calculation is complete.

These quantum jumps are treated as errors, but pinpointing exactly when they occur has long been difficult. The ability to detect quantum jumps could soon change that. Pairing microscopic resonators with qubits could also be used for precision sensing; Safavi-Naeini and his team have already collaborated with researchers at Caltech to detect and identify proteins in cells. Because sound is central to many modern devices, including smartphones, potential applications in those areas could also emerge. Safavi-Naeini said in a press release: "We have seen that vibrating objects can exhibit quantum behavior, a prerequisite for many of the operations required in quantum computing and sensing.

What this work demonstrates will allow us to advance the development of new quantum technologies and applications related to sound." The findings were published in the journal Science.

Implications of quantum jump detection for technology

The detection of quantum jumps in sound is a major breakthrough for quantum technology, advancing the development of quantum computing and potentially transforming sensing applications. Using an innovatively designed resonator, the team successfully detected the moments of quantum jumps in real time without disturbing the quantum state, a capability that is critical for future quantum technology applications. As quantum technology advances, more sound-related applications are likely to emerge, further pushing the boundaries of what is technologically possible.