Researchers split phonons in step toward new type of linear mechanical quantum computer
A University of Chicago team led by Prof. Andrew Cleland used an acoustic beamsplitter to put a single phonon into quantum superposition and to make two phonons interfere like photons, research published in Science on June 8, 2023.
A team at the University of Chicago's Pritzker School of Molecular Engineering, led by Prof. Andrew Cleland, used a device called an acoustic beamsplitter to "split" phonons — the quantum particles that carry sound — demonstrating a step toward a new type of quantum computer built from mechanical vibrations rather than light. The findings were published in the journal Science on June 8, 2023, according to reporting from SciTechDaily.
The lead author was graduate student Hong Qiao, with co-authors Chris Conner, Rhys Povey, Jacob Miller, Yash Joshi, Haoxiong Yan and Xuntao Wu, plus postdoctoral researcher Gustav Andersson, per SciTechDaily's account. The team also has a joint affiliation with Argonne National Laboratory, which separately reported on the work.
Cleland described the result as confirmation of viability rather than a finished computer: "The outcome confirmed we have the technology we need to build a linear mechanical quantum computer," he said, according to SciTechDaily. The next step, per the same report, is building a functioning quantum logic gate from phonons — the basic operation any computer, quantum or otherwise, needs to perform calculations.
What the beamsplitter demonstrated
The experiment used surface acoustic wave phonons traveling through a lithium niobate material at extremely low temperatures, run through an acoustic beamsplitter analogous to the beamsplitters used in photonic quantum optics, SciTechDaily reported. In the first test, a single phonon entering the beamsplitter existed in a quantum superposition state — reflected and transmitted at once, rather than physically splitting in two — and that superposition was then transferred to two qubits.
In a second test, two phonons entered the beamsplitter from opposite directions and exhibited the Hong-Ou-Mandel effect, traveling together in the same output direction — the same interference behavior long established for photons. SciTechDaily's report frames this as establishing that phonons behave as the functional equivalent of photons for the purposes of linear quantum computing, a platform that has so far been built almost exclusively from light.
The framing
Cleland also addressed the broader implication of demonstrating quantum behavior in a mechanical system built from a vast number of atoms: "The bizarre aspects of quantum mechanics are not limited by size," he said, as reported by SciTechDaily, noting that an individual phonon represents the collective motion of trillions of atoms rather than a single subatomic particle.
SciTechDaily's report describes the appeal of a phonon-based platform as its direct integration with qubits — unlike photon-based linear optical quantum computing, which typically requires converting information between light and matter. That integration, the report states, could allow a hybrid quantum computer combining linear mechanical computing with qubit-based computing, though the retrieved coverage does not specify a timeline for when a working logic gate, let alone a full computer, might be achieved.
US In News compiled this archived account from contemporaneous coverage by SciTechDaily. It restores a story originally published on this site in June 2023; figures are as reported at the time.