From Strongly Interacting Bose Fermi Mixtures To Ultracold Molecules
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From Strongly Interacting Bose Fermi Mixtures To Ultracold Molecules
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Author : Zoe Ziyue Yan
language : en
Publisher:
Release Date : 2020
From Strongly Interacting Bose Fermi Mixtures To Ultracold Molecules written by Zoe Ziyue Yan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
This thesis describes experiments on ultracold quantum gases. First, I discuss quantum simulation involving mixtures of bosonic and fermionic atoms. Second, I present work on creating and controlling ultracold dipolar molecules of 23Na40K. The rich phase diagram of Bose-Fermi mixtures was studied with our system of bosonic 23Na and fermionic 40K atoms. When the fermions were immersed as a minority species within a Bose-Einstein condensate, the system realized the canonical Bose polaron quasiparticle, which is an important paradigm in condensed matter physics. We investigated the strongly-coupled Bose polaron as it approached the quantum critical regime of the Bose-Fermi mixture. Using radiofrequency spectroscopy, we probed the binding energy and decay rate as a function of temperature. In particular, the decay rate was found to scale linearly with temperature near the Planckian rate k[subscript B]T/h− in the unitarity-limited regime, a hallmark of quantum critical behavior. Bose-Fermi mixtures host a complex spectrum of collective excitations, which can shed light on their properties such as collisional relaxation rates, equilibrium equations of state, and kinetic coefficients. We probed the low-lying collective modes of a Bose-Fermi mixture across different interaction strengths and temperatures. The spin-polarized fermions were observed to transition from ballistic to hydrodynamic flow induced by interactions with the bosonic excitations. Our measurements establish Bose-Fermi mixtures as a fruitful arena to understand hydrodynamics of fermions, with important connections to electron hydrodynamics in strongly-correlated 2D materials. The second part of this thesis describes the creation and manipulation of ultracold molecules in their ground state. Molecules have more tunable degrees of freedom compared to atoms, paving the way for studies of quantum state-controlled chemistry, quantum information, and exotic phases of matter. We created loosely-bound Feshbach molecules from ultracold atoms, then transferred those molecules to their absolute electronic, vibrational, rotational, and hyperfine ground state by stimulated Raman adiabatic passage. The rotational level structure, sample lifetimes, and coherence properties were studied, culminating in a demonstration of second-scale nuclear spin coherence times in an ensemble of NaK. Controlling the intermolecular interactions - which can be tunable, anisotropic, and long range - is an outstanding challenge for our field. We induced strong dipolar interactions via the technique of microwave dressing, an alternative to using static electric fields to polarize the molecules. The origin of these dipolar collisions was the resonant alignment of the approaching molecules' dipoles along their intermolecular axis, resulting in strong attraction. Our observations were explained by a conceptually simple two-state picture based on the Condon approximation.
Strongly Interacting Quantum Mixtures Of Ultracold Atoms
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Author : Cheng-Hsun Wu (Ph. D.)
language : en
Publisher:
Release Date : 2013
Strongly Interacting Quantum Mixtures Of Ultracold Atoms written by Cheng-Hsun Wu (Ph. D.) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
This thesis describes the construction of a new apparatus for ultracold quantum gases as well as the scientific results this machine has produced so far. This new apparatus is capable of simultaneously cooling and trapping lithium, sodium, and potassium. It therefore provides a platform to study a large variety of quantum mixtures. Three main experimental results are presented. Firstly, the direct cooling of "K to Bose-Einstein condensation is presented. Then the 41K atoms provide the coolant for 6Li and 40K, achieving a triply degenerate gas of 6Li -40K -41K. In particular, a broad interspecies Feshbach resonance between 40K -41K is observed, opening a new pathway to study a strongly interacting isotopic Bose-Fermi mixture of 40K -41K. Secondly, a new Bose-Fermi mixture of 23Na -40K is introduced. We show that 23Na is a very efficient coolant for 40K by sympathetically cooling 40K to quantum degeneracy with the help of a 23Na condensate. Moreover, over thirty interspecies Feshbach resonances are identified, paving the way to study strongly interacting Bose- Fermi problems, in particular the Bose polaron problem. Thirdly, we report on the first formation of ultracold fermionic Feshbach molecules of 23Na40K by radio-frequency association. The lifetime of the nearly degenerate molecular gas exceeds 100 ms in the vicinity of the Feshbach resonance. The NaK molecule features chemical stability in its ground state in contrast to the case of the KRb molecule. Therefore, our work opens up the prospect of creating chemically stable, fermionic ground state molecules of 23Na40K where strong, long-range dipolar interactions will set the dominant energy scale. Finally, the thesis concludes with an outlook on future topics in polaron physics and quantum dipolar gases, which can be studied using the new apparatus.
Ultracold Molecules From Ultracold Atoms
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Author : Caleb A. Christensen
language : en
Publisher:
Release Date : 2011
Ultracold Molecules From Ultracold Atoms written by Caleb A. Christensen and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
The thesis presents results from experiments in which ultracold Sodium-6 and Lithium-23 atomic gases were studied near a Feshbach resonance at high magnetic fields. The enhanced interactions between atoms in the presence of a molecular state enhance collisions, leading to inelastic decay and loss, many-body dynamics, novel quantum phases, and molecule formation. Experimental data is presented alongside relevant theory and numerical models. Results are presented for both homonuclear Na 2 and Li 2 molecules, as well as heteronuclear NaLi resonances, although we were unable to isolate and measure NaLi molecules. Furthermore, experiments and theories related to strongly-correlated quantum phases such as Stoner model ferromagnetism, Bose mediated Fermi interactions, and Bose-Fermi mixtures are presented as applicable to Na and Li gases. Conclusions are presented regarding the feasibility of producing deeply bound, dipolar NaLi molecules, as well as future prospects for strongly interacting atomic gases of Na and Li.
Ultracold Bosonic And Fermionic Gases
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Author : Kathryn Levin
language : en
Publisher: Elsevier
Release Date : 2012-07-30
Ultracold Bosonic And Fermionic Gases written by Kathryn Levin and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-07-30 with Science categories.
The rapidly developing topic of ultracold atoms has many actual and potential applications for condensed-matter science, and the contributions to this book emphasize these connections. Ultracold Bose and Fermi quantum gases are introduced at a level appropriate for first-year graduate students and non-specialists such as more mature general physicists. The reader will find answers to questions like: how are experiments conducted and how are the results interpreted? What are the advantages and limitations of ultracold atoms in studying many-body physics? How do experiments on ultracold atoms facilitate novel scientific opportunities relevant to the condensed-matted community? This volume seeks to be comprehensible rather than comprehensive; it aims at the level of a colloquium, accessible to outside readers, containing only minimal equations and limited references. In large part, it relies on many beautiful experiments from the past fifteen years and their very fruitful interplay with basic theoretical ideas. In this particular context, phenomena most relevant to condensed-matter science have been emphasized. Introduces ultracold Bose and Fermi quantum gases at a level appropriate for non-specialists Discusses landmark experiments and their fruitful interplay with basic theoretical ideas Comprehensible rather than comprehensive, containing only minimal equations
Interactions In Ultracold Gases
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Author : Matthias Weidemüller
language : en
Publisher: John Wiley & Sons
Release Date : 2011-02-10
Interactions In Ultracold Gases written by Matthias Weidemüller and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-02-10 with Science categories.
Arising from a workshop, this book surveys the physics of ultracold atoms and molecules taking into consideration the latest research on ultracold phenomena, such as Bose Einstein condensation and quantum computing. Several reputed authors provide an introduction to the field, covering recent experimental results on atom and molecule cooling as well as the theoretical treatment.
Quantum Matter At Ultralow Temperatures
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Author : M. Inguscio
language : en
Publisher: IOS Press
Release Date : 2016-09-27
Quantum Matter At Ultralow Temperatures written by M. Inguscio and has been published by IOS Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-09-27 with Science categories.
The Enrico Fermi summer school on Quantum Matter at Ultralow Temperatures held on 7-15 July 2014 at Varenna, Italy, featured important frontiers in the field of ultracold atoms. For the last 25 years, this field has undergone dramatic developments, which were chronicled by several Varenna summer schools, in 1991 on Laser Manipulation of Atoms, in 1998 on Bose-Einstein Condensation in Atomic Gases, and in 2006 on Ultra-cold Fermi Gases. The theme of the 2014 school demonstrates that the field has now branched out into many different directions, where the tools and precision of atomic physics are used to realise new quantum systems, or in other words, to quantum-engineer interesting Hamiltonians. The topics of the school identify major new directions: Quantum gases with long range interactions, either due to strong magnetic dipole forces, due to Rydberg excitations, or, for polar molecules, due to electric dipole interactions; quantum gases in lower dimensions; quantum gases with disorder; atoms in optical lattices, now with single-site optical resolution; systems with non-trivial topological properties, e.g. with spin-orbit coupling or in artificial gauge fields; quantum impurity problems (Bose and Fermi polarons); quantum magnetism. Fermi gases with strong interactions, spinor Bose-Einstein condensates and coupled multi-component Bose gases or Bose-Fermi mixtures continue to be active areas. The current status of several of these areas is systematically summarized in this volume.
Ultra Cold Fermi Gases
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Author : M. Inguscio
language : en
Publisher: IOS Press
Release Date : 2008-04-18
Ultra Cold Fermi Gases written by M. Inguscio and has been published by IOS Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008-04-18 with Science categories.
The field of cold atomic gases faced a revolution in 1995 when Bose-Einstein condensation was achieved. Since then, there has been an impressive progress, both experimental and theoretical. The quest for ultra-cold Fermi gases started shortly after the 1995 discovery, and quantum degeneracy in a gas of fermionic atoms was obtained in 1999. The Pauli exclusion principle plays a crucial role in many aspects of ultra-cold Fermi gases, including inhibited interactions with applications to precision measurements, and strong correlations. The path towards strong interactions and pairing of fermions opened up with the discovery in 2003 that molecules formed by fermions near a Feshbach resonance were surprisingly stable against inelastic decay, but featured strong elastic interactions. This remarkable combination was explained by the Pauli exclusion principle and the fact that only inelastic collisions require three fermions to come close to each other. The unexpected stability of strongly interacting fermions and fermion pairs triggered most of the research which was presented at this summer school. It is remarkable foresight (or good luck) that the first steps to organize this summer school were already taken before this discovery. It speaks for the dynamics of the field how dramatically it can change course when new insight is obtained. The contributions in this volume provide a detailed coverage of the experimental techniques for the creation and study of Fermi quantum gases, as well as the theoretical foundation for understanding the properties of these novel systems.
High Temperature Superfluidity In An Ultracold Fermi Gas
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Author : Martin W. Zwierlein
language : en
Publisher:
Release Date : 2006
High Temperature Superfluidity In An Ultracold Fermi Gas written by Martin W. Zwierlein and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
This thesis presents experiments in which a strongly interacting gas of fermions was brought into the superfluid regime. The strong interactions are induced by a Feshbach scattering resonance that allows to tune the interfermion scattering length via an external magnetic field. When a Fermi mixture was cooled on the molecular side of such a Feshbach resonance, Bose-Einstein condensation of up to 107 molecules was observed. Subsequently, the crossover region interpolating between such a Bose-Einstein condensate (BEC) of molecules and a Bardeen-Cooper-Schrieffer superfluid of long-range Cooper pairs was studied. Condensates of fermion pairs were detected in a regime where pairing is purely a many-body effect, the pairs being stabilized by the presence of the surrounding particles. Superfluidity and phase coherence in these systems was directly demonstrated throughout the crossover via the observation of long-lived, ordered vortex lattices in a rotating Fermi mixture. Finally, superfluidity in imbalanced Fermi mixtures was established, and its Clogston limit was observed for high imbalance. The gas was found to separate into a region of equal densities, surrounded by a shell at unequal densities.
Quantum Phase Transitions In The Bose Hubbard Model And In A Bose Fermi Mixture
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Author : Eric Nicholas Duchon
language : en
Publisher:
Release Date : 2013
Quantum Phase Transitions In The Bose Hubbard Model And In A Bose Fermi Mixture written by Eric Nicholas Duchon and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
Abstract: Ultracold atomic gases may be the ultimate quantum simulator. These isolated systems have the lowest temperatures in the observable universe, and their properties and interactions can be precisely and accurately tuned across a full spectrum of behaviors, from few-body physics to highly-correlated many-body effects. The ability to impose potentials on and tune interactions within ultracold gases to mimic complex systems mean they could become a theorist's playground. One of their great strengths, however, is also one of the largest obstacles to this dream: isolation. This thesis touches on both of these themes. First, methods to characterize phases and quantum critical points, and to construct finite temperature phase diagrams using experimentally accessible observables in the Bose Hubbard model are discussed. Then, the transition from a weakly to a strongly interacting Bose-Fermi mixture in the continuum is analyzed using zero temperature numerical techniques. Real materials can be emulated by ultracold atomic gases loaded into optical lattice potentials. We discuss the characteristics of a single boson species trapped in an optical lattice (described by the Bose Hubbard model) and the hallmarks of the quantum critical region that separates the superfluid and the Mott insulator ground states. We propose a method to map the quantum critical region using the single, experimentally accessible, local quantity R, the ratio of compressibility to local number fluctuations. The procedure to map a phase diagram with R is easily generalized to inhomogeneous systems and generic many-body Hamiltonians. We illustrate it here using quantum Monte Carlo simulations of the 2D Bose Hubbard model. Secondly, we investigate the transition from a degenerate Fermi gas weakly coupled to a Bose Einstein condensate to the strong coupling limit of composite boson-fermion molecules. We propose a variational wave function to investigate the ground state properties of such a Bose-Fermi mixture with equal population, as a function of increasing attraction between bosons and fermions. The variational wave function captures the weak and the strong coupling limits and at intermediate coupling we make two predictions using zero temperature quantum Monte Carlo methods: (I) a complete destruction of the atomic Fermi surface and emergence of a molecular Fermi sea that coexists with a remnant of the Bose-Einstein condensate, and (II) evidence for enhanced short-ranged fermion-fermion correlations mediated by bosons.
Pairing And Superfluidity In Strongly Interacting Fermi Gases
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Author : Christian Heinrich Schunck
language : en
Publisher:
Release Date : 2008
Pairing And Superfluidity In Strongly Interacting Fermi Gases written by Christian Heinrich Schunck and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
This thesis describes experiments with superfluid spin mixtures of ultracold fermionic 6Li atoms. The properties of the strongly interacting gas are studied in the crossover regime between Bose-Einstein condensation (BEC) of two-body bound molecules and a Bardeen-Cooper-Schrieffer (BCS) superfluid of pairs bound by many-body interactions. We obtain the homogeneous phase diagram of the two -component gas with resonant interactions. As a function of temperature and spin polarization the phase diagram shows first and second order phase transitions that merge at a tricritical point. At zero temperature a first order phase transition from a superfluid with equal spin populations to a mixed normal phase is observed at a critical spin polarization known as the Chandrasekhar-Clogston limit of superfluidity. Pairing correlations in the superfluid and normal phase are studied with radio-frequency (rf) spectroscopy. A signature of strong correlations is observed above the critical temperature but also at spin polarizations where superfluidity is quenched even at zero temperature. Significant limitations for the interpretation of these experiments due to final state interactions are overcome by the creation of new superfluid spin mixtures. The asymmetric rf dissociation spectra of the new mixture allow us to determine the spectroscopic pair size in the crossover regime. The size of the resonantly interacting pairs is found to be on the order of, but smaller than the interparticle spacing. Rf spectra of the majority component in an imbalanced system show a signature of thermally excited quasiparticles and by comparison to the minority spectra reveal changes in the nature of the binding as a function of spin polarization.
