Excitations, Rotational Dynamics, and Rotational Sensing in 2-Species Bose-Einstein Condensates

Our research involves the theoretical and experimental investigation of quantum many-body dynamics in systems of ultra-cold atoms, with the view of developing next-generation rotational sensors, and developing tools for and improving our general understanding of interacting many-body systems far from equilibrium. The central idea is based on using ultra-cold atoms with bosonic spin statistics, in contrast to e.g., electrons orbiting an atomic nucleus, where two electrons with the same spin cannot occupy exactly the same energy level or orbital (fermionic spin statistics). This means that at sufficiently low temperatures a dilute atomic gas composed of such bosonic atoms undergoes a particular kind of phase transition. A phase transition is a sudden, qualitative change of state, like and ordinary gas condensing to a liquid state as the temperature is lowered. The state of matter reached in the case of very dilute, low temperature bosonic atoms is called a Bose-Einstein condensate. This can be seen as the atomic/matter equivalent of a laser; a coherent, intense source of atoms, with consequent advantages to measurement science or metrology (which in the case of light are limited by the minimum wavelength for the light to be visible and controlled by conventional optics). Atom-atom interactions are, unfortunately, typically problematical, and tend to counteract the advantages of a coherent atomic source. We will build upon a proposal (suggested one of the investigators) where the issues associated with atom-atom interactions appear to be largely avoided due to an astutely chosen experimental geometry. In the process of investigating this proposed system as well as a number of closely related issues, we will deepen our understanding of nonequilibrium dynamics (due, for example, to the crucial importance of avoiding such things as flow instabilities in any functioning rotational senser), and develop broadly applicable theoretical tools accounting for the influence and production of complicated many-body effects. As such our research falls within the EPSRC Physics Grand Challenges "Emergence and Physics Far From Equilibrium" (motivated by the fact that "dramatic collective behaviour can emerge unexpectedly in large complicated systems" and "This fundamental work will be driven by the ever-present possibility that emergent states may provide the foundations for the technologies of the future") and "Quantum Physics for New Quantum Technologies" (motivated by "Next generation quantum technologies will rely on our understanding and exploitation of coherence and entanglement" and "Success requires a deeper understanding of quantum physics and a broad ranging development of the enabling tools and technologies").

Ultracold atoms are an ideal configuration in which to investigate dynamics far from equilibrium, due to a very high degree of flexibility in their experimental configurations (varying the experimental geometry, strength of interaction, and even whether the interactions are attractive or repulsive, by appropriate combinations of magnetic, laser and microwave fields), and atomic, molecular and optical (AMO) physics systems have a superlative record in terms of precision measurement, most notably in the form of atomic clocks, which, for example, underpin the functioning of the global positioning system (GPS).

This project will contribute to: Knowledge, directly through our research (which will develop general theoretical tools for the treatment of non-equilibrium dynamics in two-or-more component Bose-Einstein condensates, applying them and comparing with experiment in the specific case of rotational dynamics and rotational sensing), and via the planned Mini-Conference (where we will gather key members of the UK cold-atom and quantum optics communities to discuss problems and future directions associated with the EPSRC physics grand challenges "Emergence and Physics Far From Equilibrium" and "Quantum Physics for New Quantum Technologies", together with selected overseas participants and our Otago and Queens project partners); People, through our training of postgraduate and postdoctoral researchers (undertaken within the supportive Joint Quantum Centre (JQC) Durham-Newcastle environment), and involvement of undergraduate students (we have a very strong record in involving project, summer and exchange students in cutting-edge research, with a significant number of associated publications); Economy, through long-term potentialities of our research in producing next-generation high-precision rotational sensors, and by producing highly skilled people due to or our training; and Society, via our outreach (particularly our intention to produce and publicly post small web-movies on aspects of our research) and internationalisation (via the mini-conference, our involvement of project partners from New Zealand and Canada, which are all part of the International Matariki Network of Universities, as is Durham) efforts. Each of these aspects (Research, Training, Undergraduate Students, Outreach, Internationalisation, Mini-Conference), and our planned efforts to ensure their success, is addressed in more detail in our "Pathways to Impact" Document.