Theoretical progress in many-body physics with ultracold dipolar gases

Kaden R. A. Hazzard

Ryan Wilson

Today, sixteen years after the realization of the first Bose-Einstein condensate (BEC), the field of ultracold many-body physics is booming. In particular, much excitement has been generated by the prospect of creating a degenerate quantum gas of dipolar atoms or molecules. Already, some experimental groups have succeeded in Bose-condensing atomic 52Cr and 164Dy, while other groups have made significant progress towards achieving degeneracy of heteronuclear molecules, such as fermionic 40K87Rb and bosonic 87Rb133Cs, where the strength of the dipolar interaction promises to be much greater than that of the already rich 52Cr condensate. Just as the creation of BEC launched a whole new field of research, dipolar BECs are likely to do the same. However, such systems present a theoretical challenge due to the long-range, anisotropic nature of the dipolar interaction. In this thesis, I present a theoretical investigation of ultracold Bose gases with dipolar interactions.\nThe first part of this thesis is dedicated to the field theoretical treatment of a quantum Bose fluid with dipolar interactions in the ultracold, dilute regime, where the system is well-described by a classical condensate field with quasiparticle excitations. The set of nonlinear integrodifferential equations that describe these objects are derived and novel methods for solving them are presented that, in general, require intricate numerical treatment. Of particular importance is the emergence of a roton mode, reminiscent of that in superfluid 4He. In the second part of this thesis, I show how the roton plays a critical role in the ground state structure and dynamics of a dipolar BEC. Full numerical simulations show that the roton can, for example, be seen in the radial density profile of a quantized vortex state or in the angular collapse and explosion of a dipolar BEC. Additionally, I show the crucial role that this roton plays in determining the transition to superfluidity in these systems. Thus, a set of novel phenomena in ultracold dipolar Bose gases is explained by the presence of the roton, and experimental signatures of these phenomena are made clear.

M. A. Baranov, M. Dalmonte, Guido Pupillo +1 more

Recent experimental breakthroughs in trapping, cooling and controlling ultracold gases of polar molecules, magnetic and Rydberg atoms have paved the way toward the investigation of highly tunable quantum systems, where anisotropic, long-range dipolar interactions play a prominent role at the many-body level. In this article we review recent theoretical studies concerning the physics of such systems. Starting from a general discussion on interaction design techniques and microscopic Hamiltonians, we provide a summary of recent work focused on many-body properties of dipolar systems, including: weakly interacting Bose gases, weakly interacting Fermi gases, multilayer systems, strongly interacting dipolar gases and dipolar gases in 1D and quasi-1D geometries. Within each of these topics, purely dipolar effects and connections with experimental realizations are emphasized.

J. Bjerlin

Лев П. Питаевский, S. Stringari

Abstract This volume introduces the basic concepts of Bose–Einstein condensation and superfluidity. It makes special reference to the physics of ultracold atomic gases; an area in which enormous experimental and theoretical progress has been achieved in the last twenty years. Various theoretical approaches to describing the physics of interacting bosons and of interacting Fermi gases, giving rise to bosonic pairs and hence to condensation, are discussed in detail, both in uniform and harmonically trapped configurations. Special focus is given to the comparison between theory and experiment, concerning various equilibrium, dynamic, thermodynamic, and superfluid properties of these novel systems. The volume also includes discussions of ultracold gases in dimensions, quantum mixtures, and long-range dipolar interactions.

Javier von Stecher