JJ Thomson Avenue
Cambridge CB3 0HE
Magnetism in atomic gases – new quantum phases
The electron has the quantum mechanical property of spin, causing it to behave as a tiny bar magnet. The phenomenon of magnetism – so familiar to us from childhood – hinges upon the cooperative behavior of myriad spinning electrons.
Atoms also have spin, typically more than the electron. Can a gas of atoms display magnetism? This is one of the principal questions I have been addressing theoretically. The short answer is yes, but our idea of magnetism has to be broadened substantially beyond the simple ferromagnetism of (say) iron due to the high spin of the particles involved. Additionally, because spin is usually conserved in a gas during the lifetime of an experiment, many of the manifestations of magnetism that I have discovered are dynamical rather than static.
In a broader context, the interplay of magnetism and superfluidity lies at the heart of a diverse array of problems in modern condensed matter physics, perhaps most notably in the continuing mystery of high-temperature superconductivity. Eventually this syzygy may have technological applications, notably in magnetometry.
Extreme conditions: low dimensions; non-equilibrium
Cold atoms have proven to be a remarkably pliant experimental material, cheerfully accommodating almost every whim of the experimentalist. Atoms have been confined by laser light to lie flat in a plane, or single file in tubes, or in periodic arrays.
The influence of the (effective) spatial dimension on the properties of matter is one of the principal themes of condensed matter physics, and it appears several times in the work of my group. As an illustrative example, consider the motion of an impurity particle in a fluid. In three dimensions the impurity has some added mass from the fluid it drags with it. In one dimension, however, the particle will accelerate when subject to a force, but then come to a halt and reverse its motion, undergoing oscillations akin to Bloch oscillations in a periodic potential. Hopefully this counterintuitive prediction will be tested in upcoming experiments.
Ultracold systems are also promising arenas for the study of nonequilibrium phenomena. Bearing in mind that equilibrium systems are all alike, while every non-equilibrium system is out of equilibrium in its own way, I have tried to frame the most significant questions in a forthcoming book.