Researchers at Harvard University have achieved a groundbreaking milestone: the first-ever demonstration of a direct interaction between a single quantum of sound (a phonon) and a single atomic spin qubit.
“When we listen to music, it takes countless phonons working together to move our eardrums and maybe even get us spinning on the dance floor. But qubits are far more sensitive: a single phonon can be enough to change their quantum state — to excite them, or, as in our experiment, to help them relax.”, Professor Marko Lončar said.
The team, led by Professor Marko Lončar, successfully engineered a nanoscale mechanical resonator around a single color-center defect in diamond. These atomic-scale defects serve as robust quantum memories. Their system now enables strong enough coupling between the spin qubit and mechanical vibrations to support quantum information storage and processing — a long-standing challenge in the field.
Mechanical resonators offer key advantages for quantum technologies: they can maintain vibrations for relatively long periods while occupying a much smaller physical space compared to electromagnetic cavities of similar frequency. This makes phonons highly promising as carriers of quantum information or as compact interconnects linking quantum processors, memories, and sensors on future chips.
Beyond information processing, the strong spin-phonon interaction allows the atomic qubit to act as an ultra-sensitive detector of its mechanical environment. It could be used to measure tiny forces, stresses, or temperature variations by “listening” to quantum-level vibrations, opening doors to advanced quantum sensing applications.
This work represents significant progress toward achieving full quantum control over spin-mechanical systems and brings practical quantum acoustic devices closer to reality.
