Kuroyanagi, Hiroki, Tsukamoto, Mitsuaki, Tsubota, Makoto
We study the effects of a random potential on Kosterlitz-Thouless (KT) transitions in two-dimensional Bose systems by means of quantum Monte Carlo simulation. We use the Bose-Hubbard model imposed on...
Quantum Kelvin-Helmholtz Instability (2009)
Takeuchi, Hiromitsu, Suzuki, Naoya, Kasamatsu, Kenichi, Saito, Hiroki, Tsubota, Makoto
We theoretically study the Kelvin-Helmholtz instability in phase-separated two-component Bose-Einstein condensates using the Gross-Pitaevskii and Bogoliubov-de Gennes models. A flat interface between...
Dynamics of Charged Quantized Vortices (2009)
Tsubota, Makoto, Adachi, Hiroyuki
We study theoretically the dynamics of charged quantized vortices (CQVs). CQVs (ion-vortex complexes) have been used as an important probe in the field of quantum hydrodynamics. Recent experimental...
Numerical Studies of Counterflow Turbulence, Velocity Distribution of Vortices (2009)
Adachi, Hiroyuki, Tsubota, Makoto
We performed the numerical simulation of quantum turbulence produced by thermal counterflow in superfluid $^{4}${\rm He} by using the vortex filament model. The pioneering work was made by Schwarz,...
Tsukamoto, Mitsuaki, Tsubota, Makoto
The hardcore-Bose-Hubbard model with random chemical potential is investigated using quantum Monte Carlo simulation. We consider two cases of random distribution of the chemical potential: a...
Quantum turbulence: From superfluid helium to atomic Bose-Einstein condensates (2009)
This article reviews recent developments in quantum fluid dynamics and quantum turbulence (QT) for superfluid helium and atomic Bose-Einstein condensates. Quantum turbulence was discovered in...
Vortex sheet in rotating two-component Bose-Einstein condensates (2008)
Kasamatsu, Kenichi, Tsubota, Makoto
We investigate vortex states of immiscible two-component Bose-Einstein condensates under rotation through numerical simulations of the coupled Gross-Pitaevskii equations. For strong intercomponent...
Takeuchi, Hiromitsu, Kasamatsu, Kenichi, Tsubota, Makoto
We propose a new type of Landau instability in trapped Bose-Einstein condensates by a helically moving environment. In the presence of quantized vortices, the instability can cause spontaneous...
Drag force on an oscillating object in quantum turbulence (2008)
Fujiyama, Shoji, Tsubota, Makoto
This paper reports results of the computation of the drag force exerted on an oscillating object in quantum turbulence in superfluid $^4$He. The drag force is calculated on the basis of numerical...
Spacetime analogue of Bose-Einstein condensates: Bogoliubov-de Gennes formulation (2008)
Kurita, Yasunari, Kobayashi, Michikazu, Morinari, Takao, Tsubota, Makoto, Ishihara, Hideki
We construct quantum field theory in an analogue curved spacetime in Bose-Einstein condensates based on the Bogoliubov-de Gennes equations, by exactly relating quantum particles in curved spacetime...
The present article reviews the recent developments in the physics of quantum turbulence. Quantum turbulence (QT) was discovered in superfluid $^4$He in the 1950s, and the research has tended toward...
Spin echo in spinor dipolar Bose-Einstein condensates (2008)
Yasunaga, Masashi, Tsubota, Makoto
We theoretically propose and numerically realize spin echo in a spinor Bose--Einstein condensate (BEC). We investigate the influence on the spin echo of phase separation of the condensate. The...
Zel'dovich-Starobinsky Effect in Atomic Bose-Einstein Condensates: Analogy to Kerr Black Hole (2007)
Takeuchi, Hiromitsu, Tsubota, Makoto, Volovik, Grigory E.
We consider circular motion of a heavy object in an atomic Bose-Einstein condensate (BEC) at $T=0{\rm K}$. Even if the linear velocity of the object is smaller than the Landau critical velocity, the...
Quantized vortices in atomic Bose-Einstein condensates (2007)
Kasamatsu, Kenichi, Tsubota, Makoto
In this review, we give an overview of the experimental and theoretical advances in the physics of quantized vortices in dilute atomic-gas Bose--Einstein condensates in a trapping potential,...
Quantum Turbulence in a Trapped Bose-Einstein Condensate (2007)
Kobayashi, Michikazu, Tsubota, Makoto
We study quantum turbulence in trapped Bose-Einstein condensates by numerically solving the Gross-Pitaevskii equation. Combining rotations around two axes, we successfully induce quantum turbulent...
Bosons in Disordered Optical Potentials (2006)
Louis, Pearl J. Y., Tsubota, Makoto
In this work we systematically investigate the condensate properties, superfluid properties and quantum phase transitions in interacting Bose gases trapped in disordered optical potentials. We...
Dynamical vortex phases in a Bose-Einstein condensate driven by a rotating optical lattice (2006)
Kasamatsu, Kenichi, Tsubota, Makoto
We present simulation results of the vortex dynamics in a trapped Bose-Einstein condensate in the presence of a rotating optical lattice. Changing the potential amplitude and the relative rotation...
Thermal dissipation in quantum turbulence (2006)
Kobayashi, Michikazu, Tsubota, Makoto
The microscopic mechanism of thermal dissipation in quantum turbulence has been numerically studied by solving the coupled system involving the Gross-Pitaevskii equation and the Bogoliubov-de Gennes...
Boojums in Rotating Two-Component Bose-Einstein Condensates (2006)
Takeuchi, Hiromitsu, Tsubota, Makoto
A boojum is a topological defect that can form only on the surface of an ordered medium such as superfluid $^3$He and liquid crystals. We study theoretically boojums appearing between two phases with...
Mitani, Akira, Tsubota, Makoto
The energy spectrum of quantum turbulence obeys Kolmogorov's law. The vortex length distribution (VLD), meaning the size distribution of the vortices, in Kolmogorov quantum turbulence also obeys a...
Modulation instability and solitary wave formation in two-component Bose-Einstein condensates (2006)
Kasamatsu, Kenichi, Tsubota, Makoto
We investigate nonlinear dynamics induced by the modulation instability of a two-component mixture in an atomic Bose-Einstein condensate. The nonlinear dynamics is examined using numerical...
Kobayashi, Michikazu, Tsubota, Makoto
We develop a model of a strongly correlated Bose fluid model in a confined potential for the purpose of analyzing the localization of Bose-Einstein condensation and the disappearance of...
Phase Separation of a Fast Rotating Boson-Fermion Mixture in the Lowest-Landau-Level Regime (2005)
Kanamoto, Rina, Tsubota, Makoto
By minimizing the coupled mean-field energy functionals, we investigate the ground-state properties of a rotating atomic boson-fermion mixture in a two-dimensional parabolic trap. At high angular...
Kolmogorov Spectrum of Quantum Turbulence (2005)
Kobayashi, Michikazu, Tsubota, Makoto
There is a growing interest in the relation between classical turbulence and quantum turbulence. Classical turbulence arises from complicated dynamics of eddies in a classical fluid. In contrast,...
Inertial Range and the Kolmogorov Spectrum of Quantum Turbulenc (2005)
Tsubota, Makoto, Kobayashi, Michikazu
Quantum turbulence is numerically studied by solving the Gross-Pitaevskii equation. Introducing both the energy dissipation at small scales and the energy injection at large scales, we succeed in...
Kobayashi, Michikazu, Tsubota, Makoto
We develop a Bose fluid model in a confined potential to consider the new quantum phase due to the localization of Bose-Einstein condensation and disappearance of superfluidity which is recently...
Vortices in multicomponent Bose-Einstein condensates (2005)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
We review the topic of quantized vortices in multicomponent Bose-Einstein condensates of dilute atomic gases, with an emphasis on that in two-component condensates. First, we review the fundamental...
Three-dimensional dynamics of vortex lattice formation in Bose-Einstein condensates (2005)
Kasamatsu, Kenichi, Machida, Masahiko, Sasa, Narimasa, Tsubota, Makoto
We numerically study the dynamics of vortex lattice formation in a rotating cigar-shaped Bose-Einstein condensate. The study is a three-dimensional simulation of the Gross-Pitaevskii equation with a...
Spin textures in rotating two-component Bose-Einstein condensates (2004)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
We investigate two kinds of coreless vortices with axisymmetric and nonaxisymmetric configurations in rotating two-component Bose-Einstein condensates. Starting from the Gross-Pitaevskii energy...
Vortex molecules in coherently coupled two-component Bose-Einstein condensates (2004)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
A vortex molecule is predicted in rotating two-component Bose-Einstein condensates whose internal hyperfine states are coupled coherently by an external field. A vortex in one component and that in...
Kasamatsu, Kenichi, Tsubota, Makoto
The dynamics of multiple domain formation caused by the modulation instability of two-component Bose-Einstein condensates in an axially symmetric trap are studied by numerically integrating the...
Nemirovskii, Sergey K., Tsubota, Makoto
We study the stochastic behavior of a set of chaotic vortex loops appeared in imperfect Bose gas. Dynamics of Bose-gas is supposed to obey Gross-Pitaevskii equation with additional noise satisfying...
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
We theoretically investigate quadrupolar collective excitations in two-component Bose-Einstein condensates and their nonlinear dynamics associated with harmonic generation and mode coupling. Under...
Dynamics of quantized vortices in superfluid helium and rotating Bose-Einstein condensates (2003)
Tsubota, Makoto, Kasamatsu, Kenichi, Araki, Tsunehiko
In this article, we review the research on the dynamics of quantized vortices in superfluid helium and rotating Bose-Einstein condensates. First, after briefly reviewing the earlier research and...
A Kelvin-wave cascade on a vortex in superfluid $^4$He at a very low temperature (2003)
Vinen, W. F., Tsubota, Makoto, Mitani, Akira
A study by computer simulation is reported of the behaviour of a quantized vortex line at a very low temperature when there is continuous excitation of low-frequency Kelvin waves. There is no...
Instability of vortex array and transitions to turbulent states in rotating helium II (2003)
Tsubota, Makoto, Araki, Tsunehiko, Barenghi, Carlo F.
We consider superfluid helium inside a container which rotates at constant angular velocity and investigate numerically the stability of the array of quantized vortices in the presence of an imposed...
Vortex phase diagram in rotating two-component Bose-Einstein condensates (2003)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
We investigate the structure of vortex states in rotating two-component Bose-Einstein condensates with equal intracomponent but varying intercomponent coupling constants. A phase diagram in the...
Rotating Superfluid Turbulence (2003)
Tsubota, Makoto, Araki, Tsunehiko, Barenghi, Carlo. F.
Almost all studies of vortex states in helium II have been concerned with either ordered vortex lattices or disordered vortex tangles. This work studies numerically what happens in the presence of...
Nonlinear dynamics for vortex lattice formation in a rotating Bose-Einstein condensate (2002)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
We study the response of a trapped Bose-Einstein condensate to a sudden turn-on of a rotating drive by solving the two-dimensional Gross-Pitaevskii equation. A weakly anisotropic rotating potential...
Competition between rotation and turbulence in superfluid He$^4$ (2002)
Araki, Tsunehiko, Tsubota, Makoto, Barenghi, Carlo F.
Two types of vortex states have been much studied in superfluid $^4$He. The first is the vortex array in a rotating container. The second is the vortex tangle in turbulent flow. An experiment attempt...
Diffusion of an Inhomogeneous Vortex Tangle (2002)
Tsubota, Makoto, Araki, Tsunehiko, Vinen, W. F.
The spatial diffusion of an inhomogeneous vortex tangle is studied numerically with the vortex filament model. A localized initial tangle is prepared by applying a counterflow, and the tangle is...
Bose-Einstein condensation and superfluidity of dilute Bose gas in a random potential (2002)
Kobayashi, Michikazu, Tsubota, Makoto
We develop the dilute Bose gas model with random potential in order to understand the Bose system in random media such as 4He in porous glass. Using the random potential taking account of the pore...
Giant hole and circular superflow in a fast rotating Bose-Einstein condensate (2002)
Kasamatsu, Kenichi, Tsubota, Makoto, Ueda, Masahito
A fast rotating Bose-Einstein condensate confined in a quadratic-plus-quartic potential is found to dynamically generate a "giant vortex" that absorbs all phase singularities into a central low...
Energy Spectrum of Superfluid Turbulence without Normal Fluid (2002)
Araki, Tsunehiko, Tsubota, Makoto, Nemirovskii, Sergey K.
The energy spectrum of the superfluid turbulence without the normal fluid is studied numerically under the vortex filament model. Time evolution of the Taylor-Green vortex is calculated under the...
Energy Spectrum of the Random Velocity Field Induced by a Gaussian Vortex Tangle in HeII (2001)
Nemirovskii, Sergey K., Tsubota, Makoto, Araki, Tsunehiko
Using the Gaussian model of the vortex tangle (VT) arising in the turbulent superfluid HeII, we calculate the energy spectrum $E(k)$ of the 3D random velocity field induced by that VT. If the VT is...
Vortex Nucleation and Array Formation in a Rotating Bose-Einstein Condensate (2001)
Tsubota, Makoto, Kasamatsu, Kenichi, Ueda, Masahito
We study the dynamics of vortex lattice formation of a rotating trapped Bose-Einstein condensate by numerically solving the two-dimensional Gross-Pitaevskii equation, and find that the condensate...
Energy Spectrum of Vortex Tangle (2001)
Araki, Tsunehiko, Tsubota, Makoto, Nemirovskii, Sergey K.
The energy spectrum of superfluid turbulence in the absence of the normal fluid is studied numerically. In order to discuss the statistical properties, we calculated the energy spectra of the 3D...
Vortex lattice formation in a rotating Bose-Einstein condensate (2001)
Tsubota, Makoto, Kasamatsu, Kenichi, Ueda, Masahito
We study the dynamics of vortex lattice formation of a rotating trapped Bose-Einstein condensate by numerically solving the two-dimensional Gross-Pitaevskii equation, and find that the condensate...
Macroscopic quantum tunneling of two-component Bose-Einstein condensates (2001)
Kasamatsu, Kenichi, Yasui, Yukinori, Tsubota, Makoto
We show theoretically the existence of a metastable state and the possibility of decay to the ground state through macroscopic quantum tunneling in two-component Bose-Einstein condensates with...
Stochastic Dynamics of a Vortex Loop. Thermal Equilibrium (2000)
Nemirovskii, Sergey K., Kondaurova, Luiza P., Tsubota, Makoto
We study stochastic behavior of a single vortex loop appeared in imperfect Bose gas. Dynamics of Bose-condensate is supposed to obey Gross-Pitaevskii equation with additional noise satisfying...
Cascade process of vortex tangle dynamics in superfluid $^4$He without mutual friction (2000)
Araki, Tsunehiko, Tsubota, Makoto
Recently the Kelvin wave cascade process in superfluid $^4$He at very low temperatures was discussed. In this mechanism, the dynamics of the waves on the vortex lines plays an important role. In...
Dynamics of vortex tangle without mutual friction in superfluid $^4$He (2000)
Tsubota, Makoto, Araki, Tsunehiko, Nemirovskii, Sergey K.
A recent experiment has shown that a tangle of quantized vortices in superfluid $^4$He decayed even at mK temperatures where the normal fluid was negligible and no mutual friction worked. Motivated...
Josephson Current Flowing in Cyclically Coupled Bose-Einstein Condensates (1999)
Tsubota, Makoto, Kasamatsu, Kenichi
The Josephson effect in cyclically coupled Bose-Einstein condensates is studied theoretically. We analyze the simultaneous Gross-Pitaevskii equations with coupling terms between adjacent condensates....