University of Chicago researchers have made significant progress in the field of quantum sound by demonstrating high-fidelity entanglement between two acoustic wave resonators. This breakthrough, led by Professor Andrew Cleland's lab at the Pritzker School of Molecular Engineering, represents a major advancement in the science of quantum mechanics. The findings were published in Nature Communications.
Co-first author Ming-Han Chou explained, “A lot of research groups have demonstrated that they can entangle very, very small things down to the single electron. But here we can demonstrate entanglement between two massive objects.” He further noted that their platform is scalable and could serve as a unit cell for building larger quantum processors.
The entanglement achieved is not between molecules or atoms but between "phonons," which are nanoscale mechanical vibrations akin to sound. Hong Qiao, another co-first author and postdoctoral researcher in Cleland’s lab, described phonons as "quantum particles of sound" and highlighted their macroscopic nature compared to other quantum systems.
Cleland's team has been focused on this area for some time. They were pioneers in creating and detecting single phonons and were the first to entangle two phonons. Recently, Cleland was named a 2024 Vannevar Bush Faculty Fellow by the Department of Defense to continue exploring phonon-based quantum computing.
Cleland remarked on the implications of their work: "The conventional wisdom has been that quantum mechanics rules physics at the smallest scale while classical physics rules the human scale. But our ability to entangle massive objects by entangling their collective motion pushes that boundary."
The device developed by Cleland’s group involves two surface acoustic wave resonators, each with its own superconducting qubit for generating and detecting entangled phonon states. This setup allowed them to achieve high-fidelity quantum entanglement even when physically separate.
Qiao pointed out that previous demonstrations had limited fidelity but emphasized their achievement: “What we have shown here is we can go one step further to prepare more complicated entangled states.”
One challenge remains—the relatively short lifetime of the mechanical resonator limits performance. Chou identified extending this lifetime as a clear next step: “Our mechanical resonator has a relatively short lifetime... The next step is very clear: We will try to improve the mechanical resonator lifetime.”
By extending the current lifetime from about 300 nanoseconds to over 100 microseconds, researchers aim for more powerful communication or distributed quantum computing capabilities. Chou mentioned existing strategies could achieve this increase but were not utilized in initial experiments for simplicity.
The study was funded by several organizations including the U.S. Air Force Office of Scientific Research, DARPA, U.S. Army Research Office, U.S. Department of Energy Office of Science National Quantum Information Science Research Center, and National Science Foundation.
Citation: “Deterministic multi-phonon entanglement between two mechanical resonators on separate substrates.” Chou et al., Nature Communications, Feb. 7, 2025.
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