World’s first: US scientists capture quantum jump in sound in real time

Researchers at the Stanford University in the US have achieved a global first by measuring a quantum jump in sound in real time. The measurement opens up a new line of scientific exploration with potential applications in quantum computing and sensing that could be applied right away. Quantum jumps are sudden transitions in energy states of a quantum system. The concept of a quantum jump has been around for more than a 100 years, with theoretical physicist Niels Bohr being the first to propose it in 1913. It was only in 1986 that scientists first observed the jump in trapped ions, which was then followed by an observation in photons, the fundamental particles of light, in 2007. Nearly two decades later, a team of scientists led by Amir Safavi-Naeini, a physicist at Stanford University, has observed a quantum jump in phonons, the fundamental unit of sound. To explain their discovery, Safavi-Naeini cited the example of sound from a struck bell, which declines gradually over time rather than all at once. At a quantum level, though, these reductions are happening in jumps, and Safavi-Naeini’s team measured them in real time, a first-of-its-kind achievement. How did they measure it? To make this measurement, the researchers built a mechanical resonator at the scale of computer chips. The small size of the resonator allowed multiple units to be placed on a single chip. Much like a tuning fork, the resonator also rings when struck. However, the researchers built the resonator to have a ‘ring’ time of just two milliseconds. While this might sound extremely small, at the microscopic scale at which the resonator works, it is similar to a tuning fork vibrating for hours. Thus, the long resonance, or ‘ringdown time,’ of the resonator allowed the researchers to take hundreds of readings and exactly spot when its vibrations turned from 1 to 0 or made its quantum jump. Challenges and solutions A major challenge for the researchers working with a quantum system is to get the signal out of the system without disturbing its fragile state. A Stanford research team found a way to pair a resonator with a superconducting qubit so it could act as a detector. The paired qubit is how researchers were able to detect the precise moment in real time when the quantum jump occurred. More than detecting the quantum jump in real time, the research sets up the foundation stone for many quantum developments in the near future. For instance, in quantum computing, a fragile quantum state can cause errors before computations are completed. These quantum jumps are considered errors, but determining when exactly they occurred has proven difficult. The ability to detect a quantum jump could soon change. The microscopic resonator and qubit pairing can also be used for precise sensing, something Safavi-Naeini and his team are already working on with researchers at Caltech to detect and identify proteins in cells. Since sound is integral to a large number of modern devices like smartphones, potential applications could also evolve in these fields. “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,” said Safavi-Naeini in a press release. “What this study shows will allow us to move forward with developing new quantum technologies with sound,” concluded the researcher. The research findings were published in the journal Science. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.