Calorimetry and Thermal Transport at the Quantum Limit

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w:\awards\awards96\num.doc 9705411 Roukes Calorimetry and Thermal Transport at the Quantum Limit. This new research program focuses on reduced-dimensional heat flow and thermal equilibration in nanostructures. The investigators have developed new techniques for the surface nanomachining of suspended semiconductor structures that enable the construction of miniature, thermally-isolated devices. These possess integral transducers permitting the local introduction of heat, and local temperature measurements. Coupling these with high sensitivity dc SQUID-based methods for electron thermometry at millikelvin temperatures is ultimately expected to yield sensitivity sufficient for exploration of energy exchange processes involving individual quanta. Single- phonon phenomena, with analogs in classical and quantum optics, should become observable. Intriguing possibilities include phonon shot noise, phonon bunching, anticorrelated electron- phonon relaxation, and the phonon-by-phonon energy decay of a quasi-isolated thermal reservoir. With this level of sensitivity, calorimetry experiments elucidating processes involving individual atoms and molecules are also possible. %%% Calorimetry and Thermal Transport at the Quantum Limit. This new research program focuses on the question of how heat flows in extremely small objects, i.e. nanostructures. Ultrasmall systems can behave as if they are reduced- dimensional (i.e., less than 3D). At low temperatures, for systems that are small enough, heat flow and thermal equilibration will ultimately occur by the exchange of individual energy quanta. This domain, where heat transfer is "granular" (delivered quanta-by-quanta rather than as a steady flow) remains completely unexplored. A complete understanding of these issues will become crucial with the continued miniaturi zation of devices leading to nanotechnology. These studies are now possible through new nanomachining techniques developed by the investigators, allowing the creation of suspended, ultrasmall semiconductor structures with three- dimensional relief -- with on-board electronic measurement circuitry. Among possible applications of this research, these experiments should enable direct observation of the heat evolved during chemical reactions involving *individual* atoms and molecules. The devices developed should also offer unprecedented sensitivity for measurement of optical and infrared radiation. ***