An Interaction-Mediated Double Well Potential for Ultracold Atoms

Since the development of laser cooling techniques in the 1980s, ultracold atoms are now utilised extensively as an ideal testing ground for quantum mechanics: they can be largely isolated from environmental disturbance and properties such as density, interaction strengths and temperature are freely tuneable. This ability to investigate behaviour spanning several orders of magnitude allows us to examine an enormous array of physical predictions. Perhaps most notable is that cooling a certain class of particle down to billionths of degrees above absolute zero leads to a phase transition, producing a distinct state of matter called a Bose-Einstein condensate (BEC). Since their experimental realisation in 1995, BECs have been widely used to investigate predictions of superfluidity, quantum vortices and several other macroscopic quantum mechanical effects. Ultracold atom research appears regularly in high-impact journals and experimental findings are of great interest to those in a wide range of research fields. Recently BECs have been used to simulate the Hubbard model, the leading description of high-temperature superconductors, and several groups are working towards realising laboratory analogues of cosmological effects such as Hawking radiation and pair production. As part of our proposed programme of research, we will study the interactions between two species of atom when they interact with oscillating magnetic fields. Light itself takes the form of an oscillating magnetic field that travels in space, so understanding the dynamics that arise when different atoms interact under the influence of such a field is of enormous importance in developing a complete description of the natural world. In addition to investigating how these interactions are dependent on the properties of the oscillatory magnetic field, we aim to utilise the spatial confinement, which arises when the atoms are irradiated, to probe atomic interactions. In the BCS Hamiltonian, which describes the pairing of electrons within a superconductor to form a frictionless flow of charge, a field of vibrations mediates inter-electron interactions. It is this field which causes a typically repulsive inter-electron interaction to become attractive, leading to the formation of Cooper pairs. The low energy excitation spectrum within a BEC is analogous to the BCS vibration field. We will combine our trapping potentials and ultracold quantum gas mixture in order to investigate how the interactions between two ultracold clouds of a single species of atom can be influenced by the presence of a mediating BEC of a different atomic species. This scheme will allow us to simulate Cooper pairing and investigate the effect of oscillating magnetic fields on the BCS mechanism, providing greater insight into the mechanism of superconductivity. Over recent years, the Ultracold Matter Group in Oxford have pioneered the 'multiple radio-frequency dressed potential' method of confining ultracold gases. The method provides a high level of versatility, which allows us to investigate the properties of ultracold gases when they are confined within single wells, double well or box-like potentials. Our experimental apparatus has a unique set of capabilities: we combine smooth, confining potentials for multiple species of atom with tightly-focussed optical probes, high-power microwave fields and multiple high-resolution imaging systems. This novel approach enables study of a wide-array of physical predictions and places us in a unique position to investigate interaction-mediated effects. The project falls under the EPSRC's research theme of 'physical science' and under the research areas of 'cold atoms and molecules' as well as 'light matter interaction and optical phenomena'. Adam was responsible for preparing and submitting a grant proposal to nVidia Corporation in August 2018. The application was successful and we have recently received a GPU, which will shortly be implemented.