Abstract : The Bose-Einstein condensation (BEC) laboratory at the University of Arizona has built a program of research that focuses on two areas of BEC physics. First, we developed techniques necessary to experimentally investigate dynamic quasi-condensed states. With our system, we have instituted new directions of experimental BEC physics: studying spontaneous formation of topological defects during the BEC phase transition, and studying transitions to superfluid turbulent states. As phase transitions and turbulence occur throughout natural phenomena, this work is further relevant to a wide range of subjects in physics. Our first published results have been enabled using the support of ARO award DAAD19-03-1-0368; our research in these areas is also ongoing. Our second main efforts have revolved around refining capabilities for studying and manipulating vortices and ultra-cold gases in disc-shaped and annular potentials using optical potentials, with a particular eye towards quantum engineering of vortex and persistent current states. These efforts involve often separate areas of investigation: manipulating condensates with laser light, two-dimensional physics, fluid dynamics and turbulence, phase-transition dynamics, and vortices and persistent currents. Our efforts are collaborative, with theoretical work at multiple universities and experimental work in Arizona progressing in tandem.
Abstract : The Bose-Einstein condensation (BEC) laboratory at the University of Arizona has built a program of research that focuses on two areas of BEC physics. First, we developed techniques necessary to experimentally investigate dynamic quasi-condensed states. With our system, we have instituted new directions of experimental BEC physics: studying spontaneous formation of topological defects during the BEC phase transition, and studying transitions to superfluid turbulent states. As phase transitions and turbulence occur throughout natural phenomena, this work is further relevant to a wide range of subjects in physics. Our first published results have been enabled using the support of ARO award DAAD19-03-1-0368; our research in these areas is also ongoing. Our second main efforts have revolved around refining capabilities for studying and manipulating vortices and ultra-cold gases in disc-shaped and annular potentials using optical potentials, with a particular eye towards quantum engineering of vortex and persistent current states. These efforts involve often separate areas of investigation: manipulating condensates with laser light, two-dimensional physics, fluid dynamics and turbulence, phase-transition dynamics, and vortices and persistent currents. Our efforts are collaborative, with theoretical work at multiple universities and experimental work in Arizona progressing in tandem.
Phase transitions abound in the physical world, from the subatomic length scales of quark condensation to the decoupling forces in the early universe. In the Bose-Einstein condensation phase transition, a gas of trapped bosonic atoms is cooled to a critical temperature. Below this temperature, a macroscopic number of atoms suddenly starts to occupy a single quantum state; these atoms comprise the Bose-Einstein condensate (BEC). The dynamics of the BEC phase transition are the focus of this dissertation and the experiments described here have provided new information on the details of BEC formation. New theoretical developments are proving to be valuable tools for describing BEC phase transition dynamics and interpreting new experimental results. With their amenability to optical manipulation and probing along with the advent of new microscopic theories, BECs provide an important new avenue for gaining insight into the universal dynamics of phase transitions in general.Spontaneous symmetry breaking in the system's order parameter may be one result of cooling through a phase transition. A potential consequence of this is the spontaneous formation of topological defects, which in a BEC appear as vortices. We experimentally observed and characterized the spontaneous formation of vortices during BEC growth. We attribute vortex creation to coherence length limitations during the initial stages of the phase transition. Parallel to these experimental observations, theory collaborators have used the Stochastic Gross-Pitaevski Equation formalism to simulate the growth of a condensate from a thermal cloud. The experimental and theoretical statistical results of the spontaneous formation of vortex cores during the growth of the condensate are in good quantitative agreement with one another, supporting our understanding of the dynamics of the phase transition. We believe that our results are also qualitatively consistent with the Kibble-Zurek mechanism, a universal model for topological defect formation.Ultimately, our understanding of the dynamics of the BEC phase transition may lead to a broader understanding of phase transitions in general, and provide new insight into the development of coherence in numerous systems.
Under suitable experimental conditions, collective spin-wave excitations, magnons, form a Bose–Einstein condensate (BEC), where the spins precess with a globally coherent phase. Bose–Einstein condensation of magnons has been reported in a few systems, including superfluid phases of 3He, solid state systems, such as yttrium-iron-garnet films, and cold atomic gases. The superfluid phases of 3He provide a nearly ideal test bench for coherent magnon physics owing to experimentally proven spin superfluidity, the long lifetime of the magnon condensate, and the versatility of the accessible phenomena. We first briefly recap the properties of the different magnon BEC systems, with focus on superfluid 3He. The main body of this review summarizes recent advances in the application of magnon BEC as a laboratory to study basic physical phenomena connecting to diverse areas from particle physics and cosmology to vortex dynamics and new phases of condensed matter. This line of research complements the ongoing efforts to utilize magnon BECs as probes and components for potentially room-temperature quantum devices. In conclusion, we provide a roadmap for future directions in the field of applications of magnon BEC to fundamental research.
Since its realization in dilute bosonic atomic gases [], [], Bose-Einstein condensation of alkali atoms and hydrogen has been produced and studied extensively in the laboratory [], and has permitted an intriguing glimpse into the macroscopic quantum world. In view of potential applications [], [], [], the study of quantized vortices, which are well-known signatures of superfluidity, is one of the key issues. In fact, bulk superfluids are distinguished from normal fluids by their ability to support dissipationless flow. Such persistent currents are intimately related to the existence of quantized vortices, which are localized phase singularities with integer topological charge []. The superfluid vortex is an example of a topological defect that is well known in superconductors [] and in liquid helium []. The occurrence of quantized vortices in superfluids has been the focus of fundamental theoretical and experimental work []. Different research groups have obtained quantized vortices in Bose-Einstein condensates (BECs) experimentally, e.g., the JILA group [], [], the ENS group [] and the MIT group [], []. Currently, there are at least two typical ways to generate quantized vortices from a BEC ground state: (i) impose a laser beam rotating with an angular velocity on the magnetic trap holding the atoms to create a harmonic anisotropic potential [], [], []; or (ii) add to the stationary magnetic trap a narrow, moving Gaussian potential, representing a far-blue detuned laser [], [], [], [], [], [].
Turbulence in classical fluids has been the subject of scientific study for centuries, yet there is still no complete general theory of classical turbulence connecting microscopic physics to macroscopic fluid flows, and this remains one of the open problems in physics. In contrast, the phenomenon of quantum turbulence in superfluids has well-defined theoretical descriptions, based on first principles and microscopic physics, and represents a realm of physics that can connect the classical and quantum worlds. Studies of quantum turbulence may thus be viewed as a path for progress on the long-standing problem of turbulence.A dilute-gas Bose-Einstein condensate (BEC) is, in most cases, a superfluid that supports quantized vortices, the primary structural elements of quantum turbulence. BECs are particularly convenient systems for the study of vortices, as standard techniques allow the microscopic structure and dynamics of the vortices to be investigated. Vortices in BECs can be created and manipulated using a variety of techniques, hence BECs are potentially powerful systems for the microscopic study of quantum turbulence.This dissertation focuses on quantized vortices in BECs, specifically experimental and numerical studies of their formation, dynamics, and decay, in an effort to understand the microscopic nature of vortices as elements of quantum turbulence. Four main experiments were performed, and are described in the main chapters of this dissertation, after introductions to vortices, experimental methods, and turbulence are presented. These experiments were aimed at understanding various aspects of how vortices are created and behave in a superfluid system. They involved vortex dipole nucleation in the breakdown of superfluidity, persistent current generation from a turbulent state in the presence of energy dissipation, decay of angular momentum of a BEC due to trapping potential impurities, and exploration of the spontaneous formation of vortices during the BEC phase transition. These experiments represent progress towards enhanced understanding of the formation, dynamics, and decay of vortices in BECs and thus may be foundational to more general studies of quantum turbulence in superfluids.
Physics of ultra cold atoms and molecules is one of the most rapidly developing areas of the modern atomic, molecular, optical physics and quantum optics.This area covers several sub-areas of diverse importance, but definitely two trends can be easily identifies: i) fundamental research on properties of ultra cold atoms and molecules, and in particular atomic and molecular condensates trapped and lattice gases; here the fundamental questions of nature and form of phase transitions in degenerate systems are being posed and studied; ii) more applications oriented research on ultracold atoms and molecules, involving in particular applications in precision measurements, atomic clocks, frequency standards, atom and molecule interferometry, quantum information, quantum engineering, "super" chemistry etc.This thesis concerns both of these major trends.The applications, or more specifically quantum engineering aspect are discussed in the first four chapters of the thesis, which deal with optical manipulations of ultra cold gases, in particular optical generation of vortices in Bose condensates, quasi-solitons in Fermi gases, and retarded dipole-dipole interactions in Bose, or Fermi gases.This thesis consists of four main chapters.Chapter 2, "Optical generation of vortices in Bose Einstein Condensates".In this chapter we study theoretically the generation of vortices by phase imprinting in trapped Bose-Einstein condensates.Phase imprinting is achieved by passing a short off-resonance laser pulse through an appropriately designed absorption plate, and impinging it on a condensate.We answer the fundamental question of how the circulation and the vortex are introduced into the system, and discuss the creation of vortex arrays.We discuss vortex dynamics and interactions in such configurations.Various methods of vortex detection based on interference combined with Bragg scattering are also analyzed.In Chapter 3, "Fermionic 'Solitons'" we investigate in detail the concept of low energy excitations of ultra cold Fermi gases.This excitations are generated using the same idea of phase imprinting as that employed in the generation of vortices in BEC.We address in this chapter some questions concerning the generation (via phase imprinting) of soliton-like solutions in a single-component Fermi gas of neutral atoms at zero and finite temperatures.By using both numerical and analytical calculations, we find the conditions under which it is possible to find in non-interacting Fermi gases, quasisolitons which resemble the properties of solitons in non-linear integrable equations.We present the results for both spatially homogeneous and trapped cases, and emphasize the importance of Fermi statistics and the absence of interactions for the existence of such solutions.In Chapter 4, "Generating Dipole Condensate" we keep studying the possibilities of optical manipulations of ultracold gases.In particular, we study two different ways to laser-induce dipole-dipole interactions in trapped Bose-Einstein condensates.The first one employs the fact that those atoms in high Rydberg states posses a large dipolar moment.We first analyze the idea of imposing the dipole moment as a time average over short stroboscopic pulses.These pulses are coherently transporting the atoms from the ground atomic state to some high Rydberg state and back.The second idea is based on the observation that in strong static or oscillatory electric fields, atoms polarize and acquire dipole moment.We analyze the possibilities and limitations of inducing such a high electric field using lasers of low frequency.In Chapter 5, "Dipolar BCS", we continue our study of trapped fermionic gases, with the analysis of the BCS transition in trapped dipolar fermionic gases.We find that the critical strength of the dipole-dipole interaction to achieve BCS pairing, depends on the trap geometry.We find the particular form of this dependence, and present the solutions for the order parameter.This first chapter is meant as a general introduction to the thesis.This introduction is by no means exhaustive, and should be rather treated as a collection of basic facts concerning ultra cold gases, without rigorous derivations.The last subsection of the introductory chapter, discusses very briefly the most important achievements and trends in the field and the current state of the art.
From time to time in physics, single technical achievements have spawned an explosion of research activity and have led to the genesis of entirely new avenues of investigation. Precisely this occurred in the field of quantum gases - the topic of this Focus Issue - following the achievement of Bose-Einstein condensation in a dilute alkali gas in 1995. These experiments built on the foundational work on quantum fluids in dense systems, such as superfluid helium, and the technical achievements of laser cooling in atomic physics. Dilute quantum gases have already proved to be an incredibly fertile ground for exploring a wide range of macroscopic quantum phenomena. The rapid pace of experimental discovery and theoretical advance is evident and every year continues to bring significant achievements. A great advantage is that microscopic observations can be made directly and compared with the predictions of many-body theoretical formulations founded on interaction parameters which are completely determined - something which is not possible in their dense fluid counterparts. This Focus Issue brings together papers which cover many of the topical aspects of quantum gases: optical lattices, quantum degenerate fermions, quantum atom optics, molecular Bose-Einstein condensation, vorticity, and quantum fluctuations in systems of reduced dimensionality. One pervasive theme is the flexibility which arises from the ability to control the interactions, even dynamically if necessary. In quantum gases, this can be effected in two ways, either by changing the internal nature of the pairwise potentials by a Feshbach resonance, or by changing the nature of external potentials in which the atoms are confined and supported against gravity. The external potential may be used to spin gases to high vorticity, imprint on the system a periodic optical lattice potential, or even change the effective dimensionality. Optical lattices are particularly well represented in this Focus Issue. This is where there is the strongest connection with the physics of solids and strongly correlated fluids. Interest in optical lattices is partly due to the recent experimental demonstration that in these systems one can study the quantum phase transition from a Mott insulator, where the atoms are localized to individual sites of the optical potential, to a superfluid phase with long-range order. In contrast to a condensed matter system, the transition can be easily dynamically controlled since it is induced by simply varying the depth of the optical potential. Another area of focused interest is in fermionic gases where there is an ongoing effort, both experimentally and theoretically, to observe and characterize the high-temperature superfluid transition that should occur with enhanced pairwise interactions. If realized, this quantum system would allow experimental investigation of the crossover from Bose-Einstein condensation of dilute weakly-interacting composite bosons to the superconducting-like transition that occurs in a system of weakly interacting fermions. The topics of this Focus Issue represent well the building blocks of quantum gas studies which should allow the exploration of a wide range of macroscopic quantum phenomena in a highly controllable and clean system in which the effects of disorder may be completely absent. Given the recent progress, it will be intriguing to see where this field leads in the future. Focus on Quantum Gases Contents Anisotropic dissipation of superfluid flow in a periodically dressed Bose-Einstein condensate D M Stamper-Kurn Rapidly rotating Bose-Einstein condensates in anharmonic potentials G M Kavoulakis and Gordon Baym Feshbach resonances and collapsing Bose-Einstein condensates J N Milstein, C Menotti and M J Holland Three-body recombination of cold fermionic atoms H Suno, B D Esry and Chris H Greene Bogoliubov spectrum and Bragg spectroscopy of elongated Bose-Einstein condensates C Tozzo and F Dalfovo Quantum atom optics with Bose-Einstein condensates Klaus Mølmer Creation of effective magnetic fields in optical lattices: the Hofstadter butterfly for cold neutral atoms D Jaksch and P Zoller The Josephson frequency of resonantly coupled atomic and molecular condensates R A Duine and H T C Stoof Superfluid current disruption in a chain of weakly coupled Bose–Einstein condensates F S Cataliotti, L Fallani, F Ferlaino, C Fort, P Maddaloni and M Inguscio Bright matter wave solitons in Bose–Einstein condensates K E Strecker, G B Partridge, A G Truscott and R G Hulet Spin dynamics for bosons in an optical lattice Juan José García-Ripoll and Juan Ignacio Cirac Mean field ground state of a spin-1 condensate in a magnetic field Wenxian Zhang, Su Yi and Li You Atom resonant tunnelling through a moving barrier M L Chiofalo, M Artoni and G C La Rocca Local correlations in a strongly interacting one-dimensional Bose gas D M Gangardt and G V Shlyapnikov Shift of the molecular bound state threshold in dense ultracold Fermi gases with Feshbach resonance R Combescot Landau damping in trapped Bose condensed gases B Jackson and E Zaremba An exact reformulation of the Bose–Hubbard model in terms of a stochastic Gutzwiller ansatz Iacopo Carusotto and Yvan Castin Chemical potential standard for atomic Bose–Einstein condensates Sigmund Kohler and Fernando Sols The short-distance first-order correlation function of the interacting one-dimensional Bose gas Maxim Olshanii and Vanja Dunjko The relation between the Gross–Pitaevskii and Bogoliubov descriptions of a dilute Bose gas A J Leggett Superfluidity of Bose–Einstein condensate in an optical lattice: Landau–Zener tunnelling and dynamical instability B Wu and Q Niu Density-optimized efficiency for magneto-optical production of a stable molecular Bose–Einstein condensate Matt Mackie, Anssi Collin, Kalle-Antti Suominen and Juha Javanainen A two-atom picture of coherent atom–molecule quantum beats Bogdan Borca, D Blume and Chris H Greene Superfluid dynamics of a Bose–Einstein condensate in a periodic potential C Menotti, A Smerzi and A Trombettoni Phase diagram of two-component bosons on an optical lattice Ehud Altman, Walter Hofstetter, Eugene Demler and Mikhail D Lukin Murray J Holland University of Colorado at Boulder, USA