We study a rotating Bose-Einstein Condensate (BEC) trapped in a shifted harmonic oscillator and Mexican Hat trap, which approximates the potential of a bubble trap potential in some situations. We determined the vortices configurations that appears in this system by varying the interaction and angular momentum of the atomic cloud. The system phase diagram has the macrovortex configurations for small values of the interaction parameter. The charge of the central vortex increases with increasing rotation. Higher values of the atomic interaction turns the macrovortex unstable. It decays into multiple single-charged vortices that arrange themselves in a lattice. Since the vortices are not always visible in the absorption images, we look for alternative methods to characterize the vortex configuration. More specifically, we search for experimental signatures to determine the transitions in the phase diagram. For that, we study how the BECs velocity field affects the collective modes of the condensate. The splitting of the modes degenerescence and the increase in the mode frequency with angular velocity, which can be traced to a reduction in the gas compressibility, can be seen as an indirect signature of the presence of the vortices in the trapped BEC.
We study a rotating Bose-Einstein Condensate (BEC) trapped in a shifted harmonic oscillator and Mexican Hat trap, which approximates the potential of a bubble trap potential in some situations. We determined the vortices configurations that appears in this system by varying the interaction and angular momentum of the atomic cloud. The system phase diagram has the macrovortex configurations for small values of the interaction parameter. The charge of the central vortex increases with increasing rotation. Higher values of the atomic interaction turns the macrovortex unstable. It decays into multiple single-charged vortices that arrange themselves in a lattice. Since the vortices are not always visible in the absorption images, we look for alternative methods to characterize the vortex configuration. More specifically, we search for experimental signatures to determine the transitions in the phase diagram. For that, we study how the BECs velocity field affects the collective modes of the condensate. The splitting of the modes degenerescence and the increase in the mode frequency with angular velocity, which can be traced to a reduction in the gas compressibility, can be seen as an indirect signature of the presence of the vortices in the trapped BEC.
We study a rotating Bose-Einstein Condensate (BEC) trapped in a shifted harmonic oscillator and Mexican Hat trap, which approximates the potential of a bubble trap potential in some situations.We determined the vortices configurations that appears in this system by varying the interaction and angular momentum of the atomic cloud.The system phase diagram has the macrovortex configurations for small values of the interaction parameter.The charge of the central vortex increases with increasing rotation.Higher values of the atomic interaction turns the macrovortex unstable.It decays into multiple single-charged vortices that arrange themselves in a lattice.Since the vortices are not always visible in the absorption images, we look for alternative methods to characterize the vortex configuration.More specifically, we search for experimental signatures to determine the transitions in the phase diagram.For that, we study how the BEC's velocity field affects the collective modes of the condensate.The splitting of the modes degenerescence and the increase in the mode frequency with angular velocity, which can be traced to a reduction in the gas compressibility, can be seen as an indirect signature of the presence of the vortices in the trapped BEC.
We studied a rotating Bose–Einstein condensate confined in ring trap configurations that can be produced starting with a bubble trap confinement, approximated by a Mexican hat and shift harmonic oscillator potentials. Using a variational technique and perturbation theory, we determined the vortex configurations in this system by varying the interparticle interaction and the angular velocity of the atomic cloud. We found that the phase diagram of the system has macrovortex structures for small positive values of the interaction parameter, and the charge of the central vortex increases with rotation. Strengthening the atomic interaction makes the macrovortex unstable, and it decays into multiple singly charged vortices that arrange themselves in a lattice configuration. We also look for experimentally realizable methods to determine the vortex configuration without relying upon absorption imaging since the structures are not always visible in the latter. More specifically, we study how the vortex distribution affects the collective modes of the condensate by solving the Gross–Pitaevskii equation numerically and by analytical predictions using the sum-rule approach for the frequencies of the modes. These results reveal important signatures to characterize the macrovortices and vortex lattice transitions in the experiments.
Abstract In a harmonically-trapped rotating Bose–Einstein condensate (BEC), a vortex of large angular momentum decays to multiple vortices of unit angular momentum from an energetic consideration. We demonstrate the formation of a robust and dynamically stable giant vortex of large angular momentum in a harmonically trapped rotating BEC with a potential hill at the center, thus forming a Mexican hat like trapping potential. For a small inter-atomic interaction strength, a highly controllable stable giant vortex appears, whose angular momentum slowly increases as the angular frequency of rotation is increased. As the inter-atomic interaction strength is increased beyond a critical value, only vortices of unit angular momentum are formed, unless the strength of the potential hill at the center is also increased: for a stronger potential hill at the center a giant vortex is again formed. The dynamical stability of the giant vortex is demonstrated by real-time propagation numerically. These giant vortices of large angular momentum can be observed and studied experimentally in a highly controlled fashion.
We consider a Bose-Einstein condensate confined in a 'Mexican hat' or sombrero potential, with a quartic minus quadratic radial dependence. We find conditions under which the ground state is annular in shape, with a hole in the center of the condensate. Rotation leads to the appearance of stable multiply quantized vortices, giving rise to a superfluid flow around the ring. The collective modes of the system are explored both numerically and analytically using the Gross-Pitaevskii and hydrodynamic equations. Potential experimental schemes to detect vorticity are proposed and evaluated, which include measuring the splitting of collective-mode frequencies, observing expansion following release from the trap, and probing the momentum distribution of the condensate.
The extension of quantum phenomena into macroscopic scales is responsible for a whole class of effects such as superconductivity, superfluidity, and Bose-Einstein condensation, which played central roles in physics throughout the last century.The production of the first Bose-Einstein condensates made possible the realization of experiments involving macroscopic quantum phenomena with an unprecedented level of control of the external parameters.The persistent currents in condensates are intimately related to the nucleation of quantized vortices, which are topological defects as response to transference of quanta of angular momentum.A conventional method for generation of such defects consists in confining the condensed atomic cloud into a rotating trap.It turns out that, for angular velocities higher than a critical value, vortex states become energetically favorable, thus inducing the creation of quantized vortices.Experimental realizations of condensed alkali-metal atoms confined by more general time-dependent potentials allowed the observation not only of vortex lattices but also of quantum turbulence.Since quantum turbulence is characterized by the presence of a self-interacting tangle of quantized vortices, the correct understanding of dynamics, formation, and stability of vortices has shown to be of paramount importance being the subject of many theoretical works.In particular, the role of acoustic excitations generated by decaying multi-charged vortices in the development of turbulence is still an open question.This work aims to provide a set of tools that helps to identify the presence as well as the charge of vortices in non-turbulent clouds observed using time-of-flight pictures.We have done a detailed study of condensates containing multi-charged vortices placed at its center where time-of-flight dynamics is only one point of our interest.Due to the control that this system provides experimentally, the collective modes become an important description since they can be excited using well stablished experimental methods as such as modulation of the s-wave scattering length, and they can also be responsible to vortex decaying.For such purposes we have used the semi-analytical variational method, and the fully numerical calculation of Gross-Pitaevskii equation.Thus we have describes the collective modes that couples dynamics of vortex with the oscillation of external components of condensed atomic cloud as well as the effects in time-of-flight.The angular momentum acts increasing the kinetic energy around the vortex core, which results in a faster expansion of perpendicular direction to it.This situation shifts the frequencies of collective oscillations of a vortex-free state, and generates richer collective modes due the coupling.Now there are four possible modes, being two types of monopole mode and two types of quadrupole modes.The difference among these types is the phase of vortex oscillation.When one considers fluctuations without polar symmetry, their collective modes result in the vortex decaying.In order to control and prevent these processes we have proposed three dynamical mechanisms such as modulation of s-wave scattering length, modulation of frequencies of harmonic trap, and modulation of the amplitude of Laguerre-Gauss potential.The last one has proven to be more effective.
We consider a Bose-Einstein condensate confined in a ``Mexican hat'' or sombrero potential, with a quartic minus quadratic radial dependence. We find conditions under which the ground state is annular in shape, with a hole in the center of the condensate. Rotation leads to the appearance of stable multiply quantized vortices, giving rise to a superfluid flow around the ring. The collective modes of the system are explored both numerically and analytically using the Gross-Pitaevskii and hydrodynamic equations. Potential experimental schemes to detect vorticity are proposed and evaluated, which include measuring the splitting of collective-mode frequencies, observing expansion following release from the trap, and probing the momentum distribution of the condensate.