localization

Quantum physics is a notorious rule-breaker. For example, it makes the classical laws of thermodynamics, which describe how heat and energy move around, look more like guidelines than ironclad natural laws. In some experiments, a quantum object can keep its cool despite sitting next to something hot that is steadily releasing energy. A new experiment led by David Weld, an associate professor of physics at the University of California, Santa Barbra (UCSB), in collaboration with JQI Fellow Victor Galitski, shows that several interacting quantum particles can also keep their cool—at least for a time.

The quantum world blatantly defies intuitions that we’ve developed while living among relatively large things, like cars, pennies and dust motes. The quantum behavior of dynamical localization bucks the assumption that a cold object will always steal heat from a warmer object. Until now, dynamical localization has only been observed for single quantum objects, which has prevented it from contributing to attempts to pin down where the changeover occurs. JQI researchers and colleagues have investigated mathematical models to see if dynamical localization can still arise when many quantum particles interact. To reveal the physics, they had to craft models to account for various temperatures, interaction strengths and lengths of times. The team’s results, published in Physical Review Letters, suggest that dynamical localization can occur even when strong interactions are part of the picture.

Two physical phenomena, localization and ergodicity-breaking, are conjoined in new experimental and theoretical work.  Before we consider possible implications for fundamental physics and for prospective quantum computing, let’s first look at these two topics in turn.  It will bear providing some specific examples before getting to the quantum details.
 LOCALIZATION
When electrons pass through a material they encounter various degrees of resistance, causing them to lose energy along their journey.  In the 1950s physicist Philip Anderson, predicted that in some disordered materials (such as a semiconductors) electrons---or more specifically the electrons viewed as a series of quantum waves---could get trapped.