Credit: © 2006 Nature

As researchers continue to develop nanomechanical systems for a variety of applications, they are also following a profitable sideline in fundamental explorations of quantum mechanics. In the latest example of this, Keith Schwab of the University of Maryland and co-workers have discovered that making measurements on a nanobeam can actually lead to the structure becoming cooler1.

The beam, which is made of silicon nitride and aluminium, is 8.7 µm long, 200 nm wide and 140 nm thick. It is clamped at both ends and vibrates with a natural resonance frequency of about 21 MHz. Schwab and co-workers use a superconducting single-electron transistor (SSET) to measure the motion of the beam with a sensitivity of better than 1 femtometre. The SSET is coupled to the beam electrostatically and converts the vibrations into electrical signals.

However, the movement of the charge carriers in the SSET — both single electrons and Cooper pairs of electrons — also influences the motion of the beam. Indeed, under certain conditions this quantum ‘back-action’ can cool the beam, similar to the way that lasers can cool atomic gases.