Abstract:
The He-McKellar-Wilkens phase acquired when an electric dipole completes a circuit in a radial magnetic field, and its dual, the Aharonov-Casher Phase acquired when a magnetic dipole completes a circuit in a radial electric field, are topological phases only for specific field configurations, and even then only for configurations which cannot be exactly realised experimentally. Therefore the early work on these phases concentrated on defining the conditions under which the phases are topological and building. A major step towards the experimental realisation of the HMW phase was the observation that the electric field needed to induce the electric dipole completely changed the conditions under which the phase was topological. This led to the experimental observation of the topological HMW phase in an atomic beam, and subsequently the first atomic beam observation of the topological AC phase. I review the physics of these phases and their experimental realization.
More recently the possibility of using these phases to drive persistent current in Bose-Einstein Condensates has been pointed out. It turns out that the HWM phase can be used in this way with achievable electric and magnetic fields, but the AC phase requires unachievable fields. As I demonstrate, in this case the late-comer comes out first!
Brief Bio:
Bruce McKellar received his PhD from the University of Sydney in 1965, and was immediately appointed to the Faculty. After two years as a Member of the Institute for Advanced Study in Princeton, and a brief time in Sydney, he was appointed as Professor of Theoretical Physics at the University of Melbourne in 1972. He retired from that position in 2007 and is now an Honorary Professorial Fellow at the Centre of Excellence for Particle Physics at the Terrascale (CoEPP) in the School of Physics at the University of Melbourne. In November 2014 he became President of the International Union of Pure and Applied Physics (IUPAP), the first-ever Australian to take on this role.
His PhD was in theoretical nuclear physics. He moved to using methods of particle physics, especially current algebra, to calculate the effects of weak interactions between nucleons, and many body nucleon forces. His work on weak interactions led to calculation of the electric dipole moments expected for the nucleon and atoms in various models of these interactions. This work then evolved into studies of related CP violating effects in the B meson system.
McKellar and his students also did foundational work on the behaviour of neutrinos propagating through a dense background of neutrinos as one finds in the early universe. He Xiao-Gang of NTU and Bruce McKellar in 1993 proposed the topological phase now known as “He McKellar Wilkens” phase, independently predicted by Wilkens 1994. This phase is the subject of today’s colloquium.
In 2014, Bruce McKellar was appointed a Companion of the Order of Australia (AC),for his service to science, particularly theoretical physics, as an academic, educator and researcher, through seminal contributions to scientific development organisations, and as an author and mentor. The AC is Australia’s highest civilian honour.