Noise thermometry and electron thermometry of a sample-on-cantilever system below 1 Kelvin

We have used two types of thermometry to study thermal fluctuations in a microcantilever-based system below 1 K. We measured the temperature of a cantilevers macroscopic degree-of-freedom (via the Brownian motion of its lowest flexural mode) and its microscopic degrees-of-freedom (via the electron temperature of a metal sample mounted on the cantilever). We also measured both temperatures response to a localized heat source. We find it possible to maintain thermal equilibrium between these two temperatures and a refrigerator down to at least 300 mK. These results are promising for ongoing experiments to probe quantum effects using micromechanical devices.

Spin-exchange collisions of submerged shell atoms below 1 Kelvin

Angular momentum changing collisions can be suppressed in atoms whose valence electrons are submerged beneath filled shells of higher principle quantum number. To determine whether spin-exchange collisions are suppressed in these submerged shell atoms, we measured spin-exchange collisions of six hyperfine states of Mn at temperatures below 1 K. Although the 3d valence electrons in Mn are submerged beneath a filled 4s orbital, we find that the spin exchange rate coefficients are similar to those of Na and H (which are non-submerged shell atoms).