I. Danshita

Publications (4)10.82 Total impact

• Article: Quantum phase transition of ultracold bosons in double-well optical lattices

  I. Danshita, J. E. Williams, C. A. R. Sá de Melo, C. W. Clark
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  ABSTRACT: We study the superfluid-to-Mott insulator transition of bosons in a two-legged ladder optical lattice of a type accessible in current experiments on double-well optical lattices. The zero-temperature phase diagram is mapped out, with a focus on its dependence upon interchain hopping and the tilt between double wells. We find that the unit-filling Mott phase exhibits a nonmonotonic behavior as a function of the tilt parameter, producing a reentrant phase transition between the Mott insulator and superfluid phases. PACS numbers03.75.Hh–03.75.Lm–05.30.Jp–73.43.Nq
  Laser Physics 04/2012; 18(3):318-321. · 3.61 Impact Factor
• Article: Stability of Bose-Einstein condensates in a double-well potential

  R. Ichihara, I. Danshita, K. Egawa, T. Nikuni
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  ABSTRACT: We investigate the stability of the first excited state, the so-called “π-state,” of Bose-Einstein condensates in a double-well potential. From the condition of complex excitation energies, we determine the critical barrier height, above which the π-state is dynamically unstable. We find that the critical barrier height decreases monotonically as the number of condensate atoms increases. We also simulate the dynamics of the π-state by solving the time-dependent Gross-Pitaevskii equation. Our simulation results show that the π-state in the dynamically unstable region exhibits distinctively different behavior from that in the dynamically stable region. PACS numbers03.75.Hh–03.75.Lm–05.30.Jp–73.43.Nq
  Laser Physics 04/2012; 18(3):314-317. · 3.61 Impact Factor
• Article: Quantum phases of bosons in double-well optical lattices

  I. Danshita, J. E. Williams, C. A. R. Sá de Melo, C. W. Clark
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  ABSTRACT: We study the superfluid and insulating phases of bosons in double-well optical lattices, and focus on the specific example of a two-legged ladder, which is currently accessible in experiments. We obtain the zero-temperature phase diagram using both mean-field and time-evolving block decimation techniques. We find that the mean-field approach describes the correct phase boundaries only when the intrachain hopping is sufficiently small in comparison to the on-site repulsion. We show the dependence of the phase diagram on the interchain hopping or tilt between double wells. We find that the Mott-insulator phase at unit filling exhibits a nonmonotonic behavior as a function of the tilt parameter, producing a reentrant phase transition between Mott insulator and superfluid phases. Finally, we determine the critical point separating the insulating and superfluid phases at commensurate fillings, where the Berezinskii-Kosterlitz-Thouless transition occurs.
  Phys. Rev. A. 10/2007; 76(4).
• Article: Instability of Bose-Einstein condensates moving in optical lattices

  K. Iigaya, S. Konabe, I. Danshita, T. Nikuni
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  ABSTRACT: We investigate the Landau damping of Bogoliubov excitations in a dilute Bose gas moving in an optical lattice at a finite temperature. Using a 1D tight-binding model, we explicitly obtain the Landau damping rate, the sign of which determines the stability of the condensate. We find that the sign changes at a certain velocity, which is exactly the same as the critical velocity determined by the Landau criterion of superfluidity. This coincidence reveals the microscopic mechanism of the Landau instability.
  Laser Physics 01/2007; 17(2):215-220. · 3.61 Impact Factor