Tomasz Świsłocki

Double Universality of a Quantum Phase Transition in Spinor Condensates: Modification of the Kibble-Żurek Mechanism by a Conservation Law

We consider a phase transition from an antiferromagnetic to a phase separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We demonstrate the occurrence of two scaling laws, for the number of spin domain seeds just after the phase transition, and for the number of spin domains in the final, stable configuration. Only the first scaling can be explained by the standard Kibble-Żurek mechanism. We explain the occurrence of two scaling laws by a model including postselection of spin domains due to the conservation of condensate magnetization.

Dynamics of the modified Kibble-Żurek mechanism in antiferromagnetic spin-1 condensates

We investigate the dynamics and outcome of a quantum phase transition from an antiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We explicitly demonstrate double universality in dynamics within experiments with various quench time. Furthermore, we show that spin domains created in the nonequilibrium transition constitute a set of mutually incoherent quasicondensates. The quasicondensates appear to be positioned in a semi-regular fashion, which is a result of the conservation of local magnetization during the post-selection dynamics.

Nonadiabatic quantum phase transition in a trapped spinor condensate

We study the effect of an external harmonic trapping potential on an outcome of the nonadiabatic quantum phase transition from an antiferromagnetic to a phase-separated state in a spin-1 atomic condensate. Previously, we demonstrated that the dynamics of an untrapped system exhibits double universality with two different scaling laws appearing due to the conservation of magnetization. We show that in the presence of a trap, double universality persists. However, the corresponding scaling exponents are strongly modified by the transfer of local magnetization across the system. The values of these exponents cannot be explained by the effect of causality alone, as in the spinless case. We derive the appropriate scaling laws based on a slow diffusive-drift relaxation process in the local density approximation.

Thermal fluctuations and quantum phase transition in antiferromagnetic Bose-Einstein condensates

We develop a method for investigating nonequilibrium dynamics of an ultracold system that is initially at thermal equilibrium. Our procedure is based on the classical fields approximation with appropriately prepared initial state. As an application of the method, we investigate the influence of thermal fluctuations on the quantum phase transition from an antiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We find that at temperatures significantly lower than the critical condensation temperature

Creation of topological states of a Bose-Einstein condensate in a square plaquette of four optical traps

T_c

Resonant dynamics of chromium condensates

the scaling law for the number of created spin defects remains intact.

Improving observability of the Einstein-de Haas effect in a rubidium condensate

We study a square plaquette of four optical microtraps containing ultracold {sup 87}Rb atoms in the F=1 hyperfine state. In the presence of an external resonant magnetic field, the dipolar interactions couple the initial m{sub F}=1 component to other Zeeman sublevels. This process is a generalization of the Einstein-de Haas effect to the case when the external potential has only C{sub 4} point symmetry. We observe that vortex structures appear in the initially empty m{sub F}=0 state. Topological properties of this state arise due to competition between the local axial symmetry of the individual trap and the discrete symmetry of the plaquette. For deep microtraps vortices are localized at individual sites, whereas for shallow traps only one discrete vortex appears in the plaquette. States created in these two opposite cases have different topological properties related to C{sub 4} point symmetry.

Spinor condensate of Rb 87 as a dipolar gas

We numerically study the dynamics of a spinor chromium condensate in low magnetic fields. We show that the condensate evolution has a resonant character revealing a rich structure of resonances similar to that already discussed in the case of alkali-metal-atom condensates. This indicates that dipolar resonances occur commonly in systems of cold atoms. In fact, they have already been observed experimentally. We further simulate two recent experiments with chromium condensates in which the threshold in spin relaxation and spontaneous demagnetization phenomena were observed. We demonstrate that both these effects originate in the resonant dynamics of chromium condensates. DOI: 10.1103/PhysRevA.89.023622

Elementary excitations of a two-component Fermi system using the atomic-orbital approach

The main obstacle in the experimental realization of the Einstein–de Haas effect in a Bose-Einstein condensate is the need for very precise control of the extremely small (of the order of tens of μG) external magnetic field. In this paper, we numerically study the response of a rubidium condensate to a magnetic field that is linearly dependent on time. We find a significant transfer of atoms from the initial maximally polarized state to the next Zeeman component at magnetic fields of the order of tens of milligauss. We propose an experiment in which such a time-dependent magnetic-field-based scheme could enable the observation of the Einstein–de Haas effect in a rubidium atom condensate.

Dynamic hysteresis from bistability in an antiferromagnetic spinor condensate

We consider a spinor condensate of