Tightening the guitar strings generates faster vibrations, making the pitch go up. But when strigs are nano-sized, increased tension also reduces, or ‘dilutes,’ the loss of the string’s vibrational modes.
Crystal oscillators are ubiquitously used in electronic devices. They are known to possess extremely small mechanical energy loss at low temperatures.
By observing crystal oscillators, EPFL scientists proved that if a crystalline material with nanoscale thickness is stretched with high tension and retains its atomic order, it would be a good candidate for making strings with long-lived acoustic vibrations.
Scientists selected silicon films because of their efficiency in improving the performance of transistors. Plus, strained silicon films are commercially available in extremely small thicknesses of about 10 nanometers.
Scientists engineer nanoscale guitar strings that vibrate tens of billions of times when plucked at cryogenic temperatures using the films.
Extreme aspect ratio is a significant challenge in creating the nanostrings. In this study, the nanomechanical devices are 12 nanometers thick and 6 millimeters long.
Alberto Beccari, a Ph.D. student in Kippenberg’s lab and the paper’s first author, said, “These structures become fragile and susceptible to tiny perturbations during the last steps of their microfabrication. We had to completely revamp our fabrication protocol to be able to suspend them without catastrophic collapse.”
“The strained silicon nanostrings are particularly interesting for quantum-mechanical experiments, where their low dissipation rate provides excellent isolation from environmental disturbance, enabling the creation of high-purity quantum states.”
“A long-standing quest in fundamental physics is to study and extend the size and mass scales of objects that exhibit quantum mechanical behavior before the ever-increasing random ‘kicks’ and fluctuations from the hot, noisy environment force them to behave according to the laws of Newton mechanics. Quantum-mechanical effects have already been observed with mechanical resonators of the same size and mass, at temperatures close to the absolute zero.”
“In addition, these nano strings could be used as precision force-sensors, being subject to all sorts of interactions – for example to the minuscule radiation pressure of light beams, to weak interactions with dark matter particles and magnetic fields produced by subatomic particles.”
- A. Beccari et al. Strained crystalline nanomechanical resonators with ultralow dissipation. Nature Physics 28 February 2022. DOI: 10.1038/s41567-021-01498-4