Mechanical resonators are attracting considerable interest as sensors, signal processors, and quantum systems. Key to their remarkable performances in such diverse contexts is the combination of low mass and high quality factor. Low mass makes resonators responsive to ultra-weak perturbation; high quality factor implies that energy losses are low.
Carbon nanotubes are so small that they make the lightest resonators fabricated thus far, and as such have drawn much attention recently. Unfortunately, the quality factor of nanotube resonators has so far been somewhat modest. The demonstration of high quality factor nanotube resonators is therefore of paramount importance.
In a recent paper published in Nature Nanotechnology, Joel Moser and ICFO colleagues of the group led byAdrian Bachtold, together with Marc Dykman (Michigan university), present a carbon nanotube mechanical resonator exhibiting quality factors of up to 5 million. This represents a 30 fold improvement over the best quality factors measured in nanotubes to date. Such high quality factors reveal interesting new physics and open up a whole new realm of possibilities for sensing applications. They also pave the way for using nanotube resonators in quantum experiments. The giant quality factors that ICFO researchers have measured have not been observed before in nanotube resonators, because they are associated with vibrational states that are extremely fragile and easily perturbed by the measurement. This work reveals a new strategy to improve the quality factor of mechanical resonators.
The demonstration of quality factors of 5 million for resonators with a transverse dimension of about 1 nm comes as a surprise. For many years, researchers observed that quality factors would decrease with the volume of the resonator, and because of this trend it was unthinkable that nanotubes could exhibit giant quality factors. In this study, the NanoOptoMechanics group at ICFO demonstrates that they indeed can.