The nonequilibrium spin-changing dynamics of an ultracold mixture of lithium and sodium atoms reveals the importance of spin fluctuations for key observables. The authors show that the experimental control of fluctuations can give access to the dynamics of a long-lived metastable state, an instability region with strong growth of fluctuations, and a regime with an early approach to thermal equilibrium.
The nonequilibrium spin-changing dynamics of an ultracold mixture of lithium and sodium atoms reveals the importance of spin fluctuations for key observables. The authors show that the experimental control of fluctuations can give access to the dynamics of a long-lived metastable state, an instability region with strong growth of fluctuations, and a regime with an early approach to thermal equilibrium.
This thesis presents the experimental implementations towards the investigations of coherent spin-changing collisions in ultracold mixtures of sodium and lithium gases. The control and understanding of such spin dynamics constitutes the first step towards implementing lattice gauge theories in this experiment. For that purpose, the performance of the experimental setup was examined and improved, considering the course of the forthcoming experimental realizations. \nTo improve the spatial overlap between the atomic clouds of sodium and lithium, the vertical confinement of the crossed optical dipole trap has been increased. In addition, a versatile blue-detuned one-dimensional optical lattice has been implemented to confine both species in the same lattice site. Its characteristics and the experimental setup is described. For spin-changing collision investigations, control over the internal degrees of freedom of the atoms is crucial. We have implemented and described an actively stabilized offset magnetic field. Further, the control over the relative population between two Zeeman states of the sodium ground state is presented.
This thesis presents the investigation of the two-body scattering properties of cold atoms in \nsodium and lithium-sodium mixtures and their effects on the many body dynamics. Since both \nspecies are alkali atoms, the combined spin of both unpaired electrons can be either zero or one, \nproviding two different scattering channels. \nThe coupling of bound molecular states in these channels with the free atoms asymptote \ngives rise to the rich field of Feshbach resonance physics, where the interaction between the \nparticles can be controlled as an easily accessible experimental parameter. We have investigated \nthe Feshbach spectrum in the bosonic 7LiNa mixture and could confirm predictions based on \n6LiNa measurements, with a shift of the predicted spectrum by about 50 G. Also, the prospects \nof interaction tuning via Feshbach resonances were examined. \nThe difference of the scattering lengths of the electronic potentials also causes a coupling \nof atomic collisional channels, which can enable a spin exchange between the atoms. In this \nthesis, spin exchange processes have been studied in coherent oscillations in a thermal gas and \na Bose-Einstein condensate of sodium, as well as the evolution of this spinor gas into its ground \nstate. Preliminary studies of the heteronuclear spin exchange process in both the bosonic 7LiNa \nand in the fermionic-bosonic mixture 6LiNa are presented as well.
The dynamics and thermalization of classical systems have been extensively studied in the past. However, the corresponding quantum phenomena remain, to a large extent, uncharted territory. Recent experiments with ultracold quantum gases have at last allowed exploration of the coherent dynamics of isolated quantum systems, as well as observation of non-equilibrium phenomena that challenge our current understanding of the dynamics of quantum many-body systems. These experiments have also posed many new questions. How can we control the dynamics to engineer new states of matter? Given that quantum dynamics is unitary, under which conditions can we expect observables of the system to reach equilibrium values that can be predicted by conventional statistical mechanics? And, how do the observables dynamically approach their statistical equilibrium values? Could the approach to equilibrium be hampered if the system is trapped in long-lived metastable states characterized, for example, by a certain distribution of topological defects? How does the dynamics depend on the way the system is perturbed, such as changing, as a function of time and at a given rate, a parameter across a quantum critical point? What if, conversely, after relaxing to a steady state, the observables cannot be described by the standard equilibrium ensembles of statistical mechanics? How would they depend on the initial conditions in addition to the other properties of the system, such as the existence of conserved quantities? The search for answers to questions like these is fundamental to a new research field that is only beginning to be explored, and to which researchers with different backgrounds, such as nuclear, atomic, and condensed-matter physics, as well as quantum optics, can make, and are making, important contributions. This body of knowledge has an immediate application to experiments in the field of ultracold atomic gases, but can also fundamentally change the way we approach and understand many-body quantum systems. This focus issue of New Journal Physics brings together both experimentalists and theoreticians working on these problems to provide a comprehensive picture of the state of the field. Focus on Dynamics and Thermalization in Isolated Quantum Many-Body Systems Contents Spin squeezing of high-spin, spatially extended quantum fields Jay D Sau, Sabrina R Leslie, Marvin L Cohen and Dan M Stamper-Kurn Thermodynamic entropy of a many-body energy eigenstate J M Deutsch Ground states and dynamics of population-imbalanced Fermi condensates in one dimension Masaki Tezuka and Masahito Ueda Relaxation dynamics in the gapped XXZ spin-1/2 chain Jorn Mossel and Jean-Sébastien Caux Canonical thermalization Peter Reimann Minimally entangled typical thermal state algorithms E M Stoudenmire and Steven R White Manipulation of the dynamics of many-body systems via quantum control methods Julie Dinerman and Lea F Santos Multimode analysis of non-classical correlations in double-well Bose–Einstein condensates Andrew J Ferris and Matthew J Davis Thermalization in a quasi-one-dimensional ultracold bosonic gas I E Mazets and J Schmiedmayer Two simple systems with cold atoms: quantum chaos tests and non-equilibrium dynamics Cavan Stone, Yassine Ait El Aoud, Vladimir A Yurovsky and Maxim Olshanii On the speed of fluctuations around thermodynamic equilibrium Noah Linden, Sandu Popescu, Anthony J Short and Andreas Winter A quantum central limit theorem for non-equilibrium systems: exact local relaxation of correlated states M Cramer and J Eisert Quantum quench dynamics of the sine-Gordon model in some solvable limits A Iucci and M A Cazalilla Nonequilibrium quantum dynamics of atomic dark solitons A D Martin and J Ruostekoski Quantum quenches in the anisotropic spin-1⁄2 Heisenberg chain: different approaches to many-body dynamics far from equilibrium Peter Barmettler, Matthias Punk, Vladimir Gritsev, Eugene Demler and Ehud Altman Crossover from adiabatic to sudden interaction quenches in the Hubbard model: prethermalization and non-equilibrium dynamics Michael Moeckel and Stefan Kehrein Quantum quenches in integrable field theories Davide Fioretto and Giuseppe Mussardo Dynamical delocalization of Majorana edge states by sweeping across a quantum critical point A Bermudez, L Amico and M A Martin-Delgado Thermometry with spin-dependent lattices D McKay and B DeMarco Near-adiabatic parameter changes in correlated systems: influence of the ramp protocol on the excitation energy Martin Eckstein and Marcus Kollar Sudden change of the thermal contact between two quantum systems J Restrepo and S Camalet Reflection of a Lieb–Liniger wave packet from the hard-wall potential D Jukić and H Buljan Probing interaction-induced ferromagnetism in optical superlattices J von Stecher, E Demler, M D Lukin and A M Rey Sudden interaction quench in the quantum sine-Gordon model Javier Sabio and Stefan Kehrein Dynamics of an inhomogeneous quantum phase transition Jacek Dziarmaga and Marek M Rams
Abstract We investigate nonequilibrium steady states in an isolated system of few ultracold cesium atoms (Cs). Numerically and experimentally, we study the dynamics and fluctuations of the extracted position distributions and find the formation of nonthermal steady states for absent interactions. Atomic collisions in the s-wave regime, however, ensue thermalization of the few-particle system. We present numerical simulations of the microscopic equations of motion with a simple representation of the s-wave scattering events. Based on these simulations, a parameter range is identified, where the interaction between few atoms is sufficiently strong to thermalize the nonequilibrium steady state on experimentally accessible time scales, which can be traced by monitoring the atomic position distribution. Furthermore, the total energy distribution, which is also accessible experimentally, is found to be a powerful tool to observe the emergence of a thermal state. Our work provides a pathway for future experiments investigating the effect interactions in few-particle systems and underlines the role of fluctuations in investigating few-particle systems.
The spin dynamics of a harmonically trapped Bose-Einstein condensed binary mixture of sodium atoms is experimentally investigated at finite temperature. In the collisional regime the motion of the thermal component is shown to be damped because of spin drag, while the two condensates exhibit a counterflow oscillation without friction, thereby providing direct evidence for spin superfluidity. Results are also reported in the collisionless regime where the spin components of both the condensate and thermal part oscillate without damping, their relative motion being driven by a mean-field effect. We also measure the static polarizability of the condensed and thermal parts and we find a large increase of the condensate polarizability with respect to the T=0 value, in agreement with the predictions of theory.
Utilizing ultracold spinor gases as large-scale, many-body quantum simulation platforms, we establish a toolbox for the precise control, characterization, and detection of nonequilibrium dynamics via internal spinor phases. We develop a method to extract the phase evolution from the observed spin population dynamics, allowing us to define an order parameter that sharply identifies dynamical phase transitions over a wide range of conditions. This work also demonstrates a technique for inferring spin-dependent interactions from a single experimental time trace, in contrast to the standard approach that requires mapping a cross section of the phase diagram, with immediate applications to systems experiencing complex time-dependent interactions. Additionally, we demonstrate experimental access to and control over non-ergodic relaxation dynamics, where states of similar energy in the (nominally) thermal region of the energy spectrum retain a dependence on the initial state, via the manipulation of spinor phases, enabling the study of non-ergodic thermalization dynamics connected to quantum scarring.