Physicists at Caltech and Stanford University have engineered nanoelectromechanical systems (NEMS) capable of exhibiting quantum behavior through the intrinsic properties of their materials, a feat previously requiring an external quantum device like a superconducting qubit. This advancement simplifies the design of compact quantum sensors and qubits, opening new avenues for quantum computing and biophysics. The team achieved this by creating nonlinearity within the NEMS device; evenly spaced energy levels in linear systems hinder the ability to determine a system’s state. “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. The findings, reported in Nature Physics, represent a step toward sensors that use single phonons, the quantum version of sound waves, to detect extremely small changes in materials. NEMS Devices Enable Intrinsic Single-Phonon Quantum Behavior The ability to observe quantum behavior in the vibrations of materials, known as phonons, has significantly advanced with the development of nanoelectromechanical systems (NEMS) capable of exhibiting these properties intrinsically. This simplification promises to accelerate progress in compact quantum sensors and computing architectures. This nonlinearity is achieved by leveraging naturally occurring two-level systems, atomic-scale defects within the materials comprising the NEMS device. These defects, previously considered detrimental to quantum systems, are now harnessed to induce the desired nonlinear effects. By carefully tuning the device’s temperature and applying electromagnetic forces, the researchers resonated the NEMS with these defects, creating the conditions for single-phonon sensitivity. “It’s like a radio station, and you can tune it around to listen to the different defects,” Yuksel adds, illustrating the precision of the technique. Amir Safavi-Naeini (PhD ‘26), now an applied physics professor at Stanford