Calorimetry and Thermal Transport at the Quantum Limit

w:\awards\ wards96\num.doc 9705411量子极限下的Roukes量热法和热输运。这个新的研究项目侧重于纳米结构中的降维热流和热平衡。研究人员开发了悬浮半导体结构表面纳米加工的新技术，使微型热隔离器件的构建成为可能。这些具有完整的换能器，允许局部引入热量和局部温度测量。将这些方法与高灵敏度的基于直流squid的电子测温方法相结合，最终有望产生足够的灵敏度，用于探索涉及单个量子的能量交换过程。与经典光学和量子光学类似的单声子现象应该是可以观察到的。有趣的可能性包括声子散粒噪声、声子聚束、反相关电子-声子弛豫，以及准孤立热储的声子-声子能量衰减。有了这种灵敏度，量热法实验阐明涉及单个原子和分子的过程也是可能的。量热法和量子极限下的热输运。这个新的研究项目关注的是热量如何在极小的物体中流动，比如纳米结构。超小型系统可以表现得好像它们是降维的（即小于3D）。在低温下，对于足够小的系统，热流和热平衡最终将通过单个能量量子的交换而发生。在这个领域，热量传递是“粒状的”（一个量子一个量子地传递，而不是一个稳定的流动），仍然完全没有被探索过。随着纳米技术设备的不断小型化，对这些问题的全面理解将变得至关重要。通过研究人员开发的新型纳米加工技术，这些研究现在成为可能，允许创建具有三维浮雕的悬浮，超小型半导体结构-带有板载电子测量电路。在这项研究的可能应用中，这些实验应该能够直接观察涉及单个原子和分子的化学反应过程中产生的热量。所开发的设备还应该为光学和红外辐射的测量提供前所未有的灵敏度。*＊*

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. ***