arXiv subjects

T. Mizushima

Publications and source records attributed to T. Mizushima.

27 records · Page 2Linked to original sources

arXiv2006

Vortex structure in spinor F=2 Bose-Einstein condensates

Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a harmonic trap are solved both numerically and variationally using trial functions for each component of the wave function. Axially-symmetric vortex solutions are analyzed and energies of polar and cyclic states are calculated. The equilibrium transitions between different phases with changing of the magnetization are studied. We show that at high magnetization the ground state of the system is determined by interaction in "density" channel, and at low magnetization spin interactions play a dominant role. Although there are five hyperfine states, all the particles are always condensed in one, two or three states. Two novel types of vortex structures are also discussed.

cond-mat.other↗

arXiv2005

Topological Structure of a Vortex in Fulde-Ferrell-Larkin-Ovchinnikov State

We find theoretically that the vortex core in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is quite different from the ordinary core by a simple topological reason. The intersection point of a vortex and nodal plane of the FFLO state empties the excess spins. This leads to observable consequences in the spatial structure of the spontaneous magnetization. We analyze this topological structure based on the low lying excitation spectrum by solving microscopic Bogoliubov-de Gennes equation to clarify its physical origin.

cond-mat.supr-con↗

arXiv2005

Direct Imaging of Spatially Modulated Superfluid Phases in Atomic Fermion Systems

It is proposed that the spatially modulated superfluid phase, or the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state could be observed in resonant Fermion atomic condensates which are realized recently. We examine optimal experimental setups to achieve it by solving Bogoliubov-de Gennes equation both for idealized one-dimensional and realistic three-dimensional cases. The spontaneous modulation of this superfluid is shown to be directly imaged as the density profiles either by optical absorption or by Stern-Gerlach experiments.

cond-mat.supr-con↗

arXiv2003

Collective Oscillations of Vortex Lattices in Rotating Bose-Einstein Condensates

The complete low-energy collective-excitation spectrum of vortex lattices is discussed for rotating Bose-Einstein condensates (BEC) by solving the Bogoliubov-de Gennes (BdG) equation, yielding, e.g., the Tkachenko mode recently observed at JILA. The totally symmetric subset of these modes includes the transverse shear, common longitudinal, and differential longitudinal modes. We also solve the time-dependent Gross-Pitaevskii (TDGP) equation to simulate the actual JILA experiment, obtaining the Tkachenko mode and identifying a pair of breathing modes. Combining both the BdG and TDGP approaches allows one to unambiguously identify every observed mode.

cond-mat.soft↗

arXiv2003

Splitting of a doubly quantized vortex through intertwining in Bose-Einstein condensates

The stability of doubly quantized vortices in dilute Bose-Einstein condensates of 23Na is examined at zero temperature. The eigenmode spectrum of the Bogoliubov equations for a harmonically trapped cigar-shaped condensate is computed and it is found that the doubly quantized vortex is spectrally unstable towards dissection into two singly quantized vortices. By numerically solving the full three-dimensional time-dependent Gross-Pitaevskii equation, it is found that the two singly quantized vortices intertwine before decaying. This work provides an interpretation of recent experiments [A. E. Leanhardt et al. Phys. Rev. Lett. 89, 190403 (2002)].

cond-mat.soft↗

arXiv2002

Beliaev Damping and Kelvin Mode Spectroscopy of a Condensate in the Presence of a Vortex Line

It is demonstrated theoretically that the counter-rotating quadrupole mode in a vortex of Bose-Einstein condensates can decay into a pair of Kelvin modes via Beliaev process. We calculate the spectral weight of density-response function within Bogoliubov framework, taking account of both Beliaev and Landau processes. Good agreement with experiment on $^{87}$Rb by Bretin et al. [cond-mat/0211101] allows us to unambigiously identify the decayed mode as the Kelvin wave propagating along a vortex line.

cond-mat.soft↗

arXiv2002

Axisymmetric versus Non-axisymmetric Vortices in Spinor Bose-Einstein Condensates

The structure and stability of various vortices in F=1 spinor Bose-Einstein condensates are investigated by solving the extended Gross-Pitaevskii equation under rotation. We perform an extensive search for stable vortices, considering both axisymmetric and non-axisymmetric vortices and covering a wide range of ferromagnetic and antiferromagnetic interactions. The topological defect called Mermin-Ho (Anderson-Toulouse) vortex is shown to be stable for ferromagnetic case. The phase diagram is established in a plane of external rotation Omega vs total magnetization M by comparing the free energies of possible vortices. It is shown that there are qualitative differences between axisymmetric and non-axisymmetric vortices which are manifested in the Omega- and M-dependences.

cond-mat.soft↗

arXiv2002

Spinor Bose-Einstein Condensates with Many Vortices

Vortex-lattice structures of antiferromagnetic spinor Bose-Einstein condensates with hyperfine spin F=1 are investigated theoretically based on the Ginzburg-Pitaevskii equations near $T_{c}$. The Abrikosov lattice with clear core regions are found {\em never stable} at any rotation drive $Ω$. Instead, each component $Ψ_{i}$ $(i=0,\pm 1)$ prefers to shift the core locations from the others to realize almost uniform order-parameter amplitude with complicated magnetic-moment configurations. This system is characterized by many competing metastable structures so that quite a variety of vortices may be realized with a small change in external parameters.

cond-mat.stat-mech↗

arXiv2002

Mermin-Ho vortex in ferromagnetic spinor Bose-Einstein condensates

The Mermin-Ho and Anderson-Toulouse coreless non-singular vortices are demonstrated to be thermodynamically stable in ferromagnetic spinor Bose-Einstein condensates with the hyperfine state F=1. The phase diagram is established in a plane of the rotation drive vs the total magnetization by comparing the energies for other competing non-axis-symmetric or singular vortices. Their stability is also checked by evaluating collective modes.

cond-mat.soft↗