An Interaction-Mediated Double Well Potential for Ultracold Atoms

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

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.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1964306 Studentship EP/N509711/1 01/10/2016 30/09/2019 Adam James Barker
 
Description We have optimised our experiment using machine learning methods. The results of this study, including benchmarks of performance, have been published in a recent paper in collaboration with Google DeepMind ().

Furthermore, we have used our method of confining atomic gases to demonstrate that we can selectively manipulate the components of a mixture. We have also measure the (collisional) stability of this mixture of atoms.
Exploitation Route The machine learning methods can be used by others to guide optimisation of their own experiments.

Many others are pursuing atomic gas mixtures as a means of probing significant physical phenomena. Our methods of manipulating the individual constituents can be used to investigate turbulence and boundary instabilities between mixture constituents.
Sectors Education

URL https://arxiv.org/abs/1908.08495
 
Description To enhance our understanding of evaporative cooling towards Bose-Einstein condensation in our experimental apparatus, we have developed a 3D virtual reality simulation/game. This has been used at several outreach and offer holders events within the Department of Physics in Oxford and has been a valuable educational tool. Our ambition is to use this at other science fairs in the future.
First Year Of Impact 2018
Sector Education
Impact Types Societal

 
Description Experiment and theory collaboration between Oxford and Durham 
Organisation Durham University
Department Durham University Business School
Country United Kingdom 
Sector Academic/University 
PI Contribution We have collected experimental data on the collisional properties of two isotopes of rubidium when illuminated with high-intensity radio waves. We have used this data to determine the exact nature of the collision and associated parameters and constants.
Collaborator Contribution Our partners have provided supporting data, generated from rigorous, quantum mechanical simulations of colliding atoms. Their simulations elucidate some of the more complex features of the collision process and corroborate our approximate model. Both parties are involved in writing a research paper, which will be submitted for review to a leading journal shortly.
Impact This collaboration is multi-disciplinary, as our partners work within the field of Physical Chemistry. A research paper is current in preparation and will be submitted for publication shortly.
Start Year 2018
 
Description Virtual Reality Simulation of Atomic Cooling 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact We created and developed a virtual reality simulation/video game which has been used at several outreach events to demonstrate the principles of atomic cooling. At least 50 people have used the game at offer holders events and an evening in the physics deparment of demonstrations aimed at the local community. Many discussions were sparked and a huge number of students stopped to ask questions and take part in the game.
Year(s) Of Engagement Activity 2018,2019