OU Physicists First to Create New Molecule with Record-Setting Dipole Moment
Trilobite molecule with record dipole moment
Wavefunction amplitude of a highly excited Rydberg atom and a ground state atom
Jim Shaffer’s research group along with theorists Hossein Sadeghpour at ITAMP and Seth Rittenhouse at Western Washington University have created a new kind of molecule based on the interaction between a highly-excited Rydberg atom and a ground-state atom. A unique property of the molecule is the large permanent electric dipole moment, which reacts with an electric field much like a bar magnet reacts with a magnetic field. This molecule has the largest electric dipole moment ever observed in a molecule. A paper by the team on this research has been published in Science magazine at news.sciencemag.org, Science 348, 99-102 (2015). The work is also being highlighted in a News and Views article in Nature Physics in May.
“This is the largest electric dipole moment ever observed in a molecule,” says James Shaffer, professor in the Homer L. Dodge Department of Physics and Astronomy, OU College of Arts and Sciences. Shaffer and his team want to produce enough of these molecules to carry out future experiments on dipole interactions. Dipole interactions between particles are interesting for a number of reasons including their role in forming new states of matter and their possible use in constructing scalable quantum computers. One can readily envisage applications for these molecules ranging from ultracold chemistry to studying strongly correlated many-body physics.
Donald Booth, the lead graduate student on this project, says the molecule is formed when an electron from the Rydberg atom grabs onto the ground-state atom. The researchers excite the Rydberg atom using lasers in a cloud of ground-state atoms held at a millionth of a degree above absolute zero, so the Rydberg electron can collide with a ground-state atom and form the molecule.
These exotic states of matter are referred to as trilobite molecules because their electronic probability distributions resemble the fossilized marine creatures. Theoretically predicted by Chris Greene and co-workers in 2000, they are ultra-long range molecular Rydberg states where the Rydberg atom has a very large principal quantum number and high orbital angular momenta coupled to a ground state atom of the same species. Due to strong localization of the electron cloud these molecules are expected to possess huge permanent electric dipole moments, of the order of thousands of Debye which is quite surprising since homonuclear molecules are symmetric and therefore should not have a dipole moment in the first place.
Cesium atoms, due to peculiarities in their low orbital angular momentum energy states, can be bound in a hybrid state with a mixture of high and low orbital angular momentum states yielding permanent electric dipole moments of thousands of Debye. To put this into perspective the dipole moment of water is 1.85 Debye and even very polar molecules like sodium chloride have dipole moments of 9 Debye. Creating these molecules adds a new creature to the quantum world’s menagerie of exotic states.