When a singer belts out a tune while a guitar player strums along, sound waves travel through the air, driving collective oscillations of the molecules within. Meanwhile, at the quantum level, something similar is going on. Atoms inside materials, everything from our bodies to metals and more, naturally jiggle around, creating tiny vibrational waves that ripple across the material. These vibrations are known as phonons: the quantum version of sound waves. Now, physicists at Caltech and Stanford University have developed devices called nanoelectromechanical systems (NEMS) that allow phonons to exhibit their quantum behavior purely through the intrinsic properties of the material that makes up the device. Previously, it was not possible to observe such behavior without the help of an external quantum device, such as a superconducting qubit. This means that through this newly discovered mechanism a solitary NEMS device, can, for example, serve as a greatly simplified and very compact quantum sensor or qubit. More specifically, the goal of the work is to make the vibrations of the NEMS nonlinear. If you imagine the energy levels in a nonlinear system as steps in a ladder, it is as if the ladder steps are not evenly spaced. "You don't want linear systems for quantum applications, because then you can't tell what state the system is in—all the step changes that the system can make look the same," says Mert Yuksel (PhD '26), a Caltech postdoctoral scholar and co-lead author of the new study. "So, having nonlinearity is the goal, and now we can achieve this in the NEMS intrinsically." The new work, part of an emerging field called quantum acoustics, marks a next step toward creating quantum-sensing devices that use single phonons to precisely detect extremely small changes in materials. The findings, reported in Nature Physics, have applications in quantum