Dynamics of ultracold quantum gases in the dissipative Fermi–Hubbard model
Koen Sponselee, Lukas Freystatzky, B. Abeln, M Diem, Bastian Hundt, André Kochanke, Thomas Georg Ponath, Bodhaditya Santra, Ludwig Mathey, K. Sengstock, C Becker
Abstract We employ metastable ultracold 173 Yb atoms to study dynamics in the 1D dissipative Fermi–Hubbard model experimentally and theoretically, and observe a complete inhibition of two-body losses after initial fast transient dynamics. We attribute the suppression of particle loss to the dynamical generation of a highly entangled Dicke state. For several lattice depths and for two- and six-spin component mixtures we find very similar dynamics, showing that the creation of strongly correlated states is a robust and universal phenomenon. This offers interesting opportunities for precision measurements.
Abstract We employ metastable ultracold 173 Yb atoms to study dynamics in the 1D dissipative Fermi–Hubbard model experimentally and theoretically, and observe a complete inhibition of two-body losses after initial fast transient dynamics. We attribute the suppression of particle loss to the dynamical generation of a highly entangled Dicke state. For several lattice depths and for two- and six-spin component mixtures we find very similar dynamics, showing that the creation of strongly correlated states is a robust and universal phenomenon. This offers interesting opportunities for precision measurements.
We report an experimental study of dynamics of the metastable 3P2 state of bosonic ytterbium atoms in an optical lattice. The dissipative Bose-Hubbard system with on-site two-body atom loss is realized via its intrinsic strong inelastic collision of the metastable 3P2 atoms. We investigate the atom loss behavior with the unit-filling Mott insulator as the initial state and find that the atom loss is suppressed by the strong correlation between atoms, which is attributed to both the on-site interaction and the inelastic loss. Also, as we decrease the potential depth of the lattice, we observe the growth of the phase coherence and find its suppression owing to the dissipation.
Two-body inelastic collisions arising from chemical reactions are prevalent in ultracold fermionic and bosonic molecular gases. Although recent advancements have achieved quantum degeneracy in these systems, loss dynamics are typically modeled phenomenologically using rate equations that often assume thermalization during chemical reactions. In this study, we employ the inelastic quantum Boltzmann equation to analyze particle loss, temperature evolution, and momentum distributions in single-component Fermi gases from first principles. Our results demonstrate that the conventional particle-number rate equation accurately describes the dynamics in trapped systems but fails to capture the behavior in homogeneous systems. Notably, under pure p-wave inelastic collisions and zero elastic collisions, we find that systems prepared near or above quantum degeneracy remain in a thermal state, whereas systems initialized deep within degeneracy exhibit nonequilibrium dynamics. Our theoretical predictions align well with recent experimental observations in trapped systems, and our claim can be further verified in atomic systems with induced two-body loss in box potentials.
Atomic quantum gases in the strong-correlation regime offer unique possibilities to explore a variety of many-body quantum phenomena. Reaching this regime has usually required both strong elastic and weak inelastic interactions because the latter produce losses. We show that strong inelastic collisions can actually inhibit particle losses and drive a system into a strongly correlated regime. Studying the dynamics of ultracold molecules in an optical lattice confined to one dimension, we show that the particle loss rate is reduced by a factor of 10. Adding a lattice along the one dimension increases the reduction to a factor of 2000. Our results open the possibility to observe exotic quantum many-body phenomena with systems that suffer from strong inelastic collisions.
Ultracold atomic gases provide a fantastic platform to implement quantum simulators and investigate a variety of models initially introduced in condensed matter physics or other areas. One of the most promising applications of quantum simulation is the study of strongly correlated Fermi gases, for which exact theoretical results are not always possible with state-of-the-art approaches. Here, we review recent progress of the quantum simulation of the emblematic Fermi–Hubbard model with ultracold atoms. After introducing the Fermi–Hubbard model in the context of condensed matter, its implementation in ultracold atom systems, and its phase diagram, we review landmark experimental achievements, from the early observation of the onset of quantum degeneracy and superfluidity to the demonstration of the Mott insulator regime and the emergence of long-range anti-ferromagnetic order. We conclude by discussing future challenges, including the possible observation of high- T c superconductivity, transport properties, and the interplay of strong correlations and disorder or topology.
Ultracold quantum gases of alkaline-earth-like metals are a versatile tool to investigate interacting many-body physics by realizing clean and controllable experimental model systems. Their intriguing properties range from energetically low-lying clock transitions, which allow for high-resolution spectroscopy, over meta-stable states, which can be regarded as a second species with orbital degree of freedom, to SU(N) symmetry, allowing novel magnetic phases. These open up new possibilities for quantum simulators. Using them in combination with optical lattices dissipative Fermi-Hubbard models and the Kondo-lattice-model can be realized, two promising examples for probing strongly correlated systems.
This thesis presents an experimental apparatus for producing ultracold samples of fermionic 173Yb (N≤6). A new bicolor dipole trap was implemented with a final, average trap frequency of 36Hz. Using optical, resonant pumping and an Optical-Stern-Gerlach scheme,
the spin mixture can arbitrarily be changed from a six- to a one-component gas. Typically the degenerate Fermi gases consist of 87000 atoms at 17.5%TF (N=6) and of 47000 atoms at 19.4%TF (N=1).
The lowest lying meta-stable state 3P0 (578nm) is coherently controlled using a clock-laser setup with a linewidth of FWHM=1Hz by means of Rabi oscillations or rapid adiabatic passage. By conducting spectroscopic measurements in a 3D magic lattice (759nm) we demonstrate interband transitions and observe the 1S0⇔3P0 excitation with a resolution of FWHM=50(2)Hz. Applying these techniques to a two-component spin mixture reveals a shift of the clock-transition caused by spin-exchange interaction between the orbital symmetric |eg>(+)|↑↓>(-) and the orbital antisymmetric |eg>(-)|↑↓>(+) state.
Using the inelastic properties of the 3P0 state a dissipative Fermi-Hubbard model is realized. The dynamics in this system can not be described by a simple two-body loss model. We identify two relevant time scales and observe a spin dependence of the g(2) correlation function. The here presented apparatus and experimental results constitute an important step towards a profound understanding of strongly correlated many-body systems and for bridging the gap between quantum gases and condensed matter physics.
Ultrakalte Quantengase mit erdalkali-ahnlichen Metallen stellen ein vielseitiges Werkzeug dar, um Vielteilchensysteme mit Wechselwirkung zu untersuchen. Dabei ist man in der Lage, diese experimentellen Modellsysteme in einer sauberen und kontrollierbaren Weise umzusetzen. Durch ihre faszinierenden Eigenschaften, z.B. energetisch niedrig liegende Uhrenubergange, welche hochauflosende Spektroskopie ermoglichen, metastabile Zustande, die als unabhangige Teilchensorte mit orbitalem Freiheitsgrad betrachtet werden konnen oder SU(N)-Symmetrie, welche neuartige magnetische Phasen hervorbringen kann, konnen neue Arten von Quantensimulatoren ermoglicht werden. Im Zusammenspiel mit optischen Gittern konnen diese Metalle dissipative Fermi-Hubbard-Modelle und das Kondo-Gitter-Modell realisieren, zwei vielversprechende Beispiele fur stark korrelierte Systeme.
Diese Abschlussarbeit prasentiert einen experimentellen Aufbau zur Herstellung von ultrakalten Gasen mit 173Yb (N≤6). Eine neue, zweifarbige Dipolfalle wurde aufgebaut und erreicht eine Endfallenfrequenz von 36Hz. Durch Benutzung von resonantem, optischem Pumpen und einem Optischen-Stern-Gerlach System kann eine beliebige Spinmischung zwischen einer und sechs Komponenten erzeugt werden. Typischerweise besteht ein entartetes Fermigas aus 87000 Atomen bei 17.5%TF (N=6) und aus 47000 Atomen bei 19.4%TF (N=1).
Der niedrigst liegende metastabile Zustande 3P0 (578nm) kann mithilfe eines Uhrenlasers, dieser hat eine Linienbreite von FWHM=1Hz, durch Rabioszillationen oder einer rapiden-adiabatischen-Passage populiert werden. Durch spektroskopische Messungen in einem magischen 3D Gitter (759nm) demonstrieren wir Ubergange zwischen verschiedenen Bandern und beobachten die 1S0⇔3P0 Anregung mit einer Auflosung von FWHM=50(2)Hz. Unter Anwendung dieser Technik bei einer zweikomponentigen Mischung ergibt sich ein Frequenzversatz des Uhrenubergangs durch Spinwechselwirkung zwischen dem orbital symmetrischen |eg>(+)|↑↓>(-) und orbital antisymmetrischen |eg>(-)|↑↓>(+) Zustand.
Unter Ausnutzung der inelastischen Wechselwirkung des 3P0 Zustands wird ein dissipatives Fermi-Hubbard Modell realisiert. Die Dynamik in diesem System kann nicht mit einem einfachen Zweikorperverlust-Modell beschrieben werden. Wir identifizieren zwei relevante Zeitskalen und beobachten eine Spinabhangigkeit der g(2) Korrelationsfunktion.
Der hier vorgestelle Aufbau und die experimentellen Ergebnisse stellen einen wichtigen Schritt zum Verstandnis von stark korrelierten Vielteilchensystemen dar und verbinden die Forschungsfelder von Quantengasen und kondensierter Materie.
Ultracold bosonic gases in optical lattices are strongly correlated quantum systems similar to solids. The strong correlation between the electrons in a solid on the one hand, and the bosonic atoms in optical lattice on the other, exhibit various quantum phenomena like insulation, conductivity, localization of electrons and atoms, respectively. Controlled by the intensity of the lattice laser, the ultracold bosonic gas can be transferred from a regime with superfluid character for shallow lattices into a regime of strong correlations, the Mott insulator. As an additional external parameter besides the lattice depth, one can generate spatial inhomogeneities by superimposing an additional standing wave (so-called two-color superlattices), which gives rise to localization effects or the formation of a Bose-glass phase. In the present work, numerical simulations are employed in order to investigate characteristic signatures of the quantum phases in the low-energy excitation spectrum of one-dimensional systems. We simulate temporal small amplitude modulations of the optical lattice in analogy to experiments, and evaluate the response of the system from the time-evolved initial state. The lattice systems are described in the framework of the Bose-Hubbard model. For the evaluation of the time-evolved state, we employ several numerical methods. We analyze systems of small size (6 particles on 6 sites) using an exact time-evolution by integration of the time-dependent Schrödinger equation. The formulation of an importance truncation scheme enables us to retain only the relevant components of the model space in the strongly correlated regime and, thus, allows for the investigation of systems with 10 particles on 10 sites using exact time-evolution. Based on this method, we present results of the Mott-insulating regime as well as for the Bose-glass phase. Furthermore, we employ particle-hole methods, which allow for the treatment of systems with experimental lattice sizes and particle numbers. Starting from the equation of motion method we adapt the Tamm-Dancoff approximation as well as the random-phase approximation for the occupation number representation of the Bose-Hubbard model. We present results of simulations of up to 50 particles on 50 sites and discuss the impact of the lattice depth on the low-energy excitations (U-resonance). Moreover, the impact of a two-color superlattice and the variation of its amplitude is investigated.