Cottrell College Science Awards - 2015
Thermal Conductivity on the Nanoscale: Measuring Quantum Heat Transport with Chains of Trapped Ions
Electronic devices continue to shrink in size and consume less power; but regardless of how small and energy efficient our devices become there will always be the problem of dealing with excess heat. That’s because heat is a byproduct of activity, even at the incredibly tiny nanoscale and below, in the realm of atoms and electrons.
On the atomic scale, thermal conduction is a ballistic process, meaning that heat propagates without scattering. In contrast, on macroscopic scales conduction is diffusive, and heat “wanders” down gradients from warm to cool, as with the warming of a spoon in a hot cup of coffee.
“This regime at the crossover between ballistic and diffusive heat transport resists theoretical study,” says Stephen C. Doret, a Williams College physicist. He notes that nanoscale systems – which would include tomorrow’s shrinking electronics -- “are still too large for practical first principles atomic-scale calculations.”
Knowing precisely how heat behaves at the atomic and nano-scales is something Doret is working to achieve. To pursue that knowledge he has received a Cottrell College Science Award from Research Corporation for Science Advancement (RCSA).
The funding will support his experiments with linear chains of atomic ions trapped and isolated in a vacuum through the use of static and oscillating electric fields in a so-called Paul trap. An ion is an atom in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.
He and his students will use lasers to both heat and cool trapped calcium ions. Though often associated with heating, lasers can also be used to cool atoms through a delicate process involving repeatedly zapping the atom in just the right way to excite it into giving up more energy than it absorbs from the brief exposure to the laser.
Their goal is to measure and understand the quantum-to-classical transition from ballistic to diffusive heat transport. Specifically, they want to understand under what conditions heat transfer begins to obey Fourier’s Law of conduction – that is, when it enters the realm of classical physics, as opposed to the quantum realm of individual atoms.
“These measurements will provide insights for thermal engineering in new mesoscopic [the realm of groups of atoms to the nanoscale] devices and also guide laser cooling of ion chains for quantum information processing and quantum logic spectroscopy,” Doret said.