Atomic Motion at the Edge of Stability

L. Morales-Molina, E. Arévalo

We study the superfluid behavior motion of interacting particles in a periodic potential subject to an external ac force. We observe a dynamical stabilization of the superfluid motion in the presence of ac forces around the boundary of the Brillouin zone. We analyze relevant nonlinear Floquet-Bloch states within the mean field approximation that display loops in the energy spectrum. In particular, we investigate with some detail the transport properties of these states at the edge of the Brillouin zone, showing the existence of a nonvanishing motion of particles. These findings are corroborated by a nonlinear generalization of the Hellmann-Feynman expression for the group velocity. Our results shed new light on the observation of stable persistent motion of particles in periodic potentials.

Gunther K. Wertheim

He Zhang-Ming, Dexun ZHAI, Qianquan ZHU +1 more

Kapitza’s pendulum is an inverted pendulum that is dynamically stabilized by rapidly driving its pivot point. Many applications of Kapitza stabilization in quantum systems have been proposed, such as optical molasses, the stability of optical resonators, preparation of molecular ions, the breaking of translation symmetry, the periodically driven sine-Gordon model, polariton Rabi oscillation, and the stabilization of bright solitons in a Bose-Einstein condensate. In particular, Kapitza stabilization can be used to trap particles. The most notable example of such an application is the Paul trap. Recently, the Kapitza trap was created by superimposing time-tuned focused laser beams to produce a periodically driven harmonic potential for ultracold atomic gases. This work opens up new possibilities to study Floquet systems of ultracold atomic gases. So we consider the periodically driven harmonic potential, and investigate the properties of soliton in ultracold atomic gases by numerical simulations. It is found interestingly that when a soliton is located at the center of the harmonic potential, a resonance phenomenon of soliton amplitude oscillation occurs at a specific driven frequency. In addition, the oscillation amplitude increases with the increase of the trapping frequency of the harmonic potential, and the resonance frequency increases with theaugment of soliton initial amplitude. The change of driven frequency and initial phase has a significant effect on soliton motion when the soliton is located at the edge of the harmonic potential. When the initial phase is zero, there is a characteristic driven frequency. For the case where the driven frequency is equal to the characteristic frequency, soliton motion exhibits periodic oscillations. For the case where the driven frequency is slightly lower than the characteristic frequency, the resonance of soliton oscillation can be found. When the driven frequency is slightly higher than the characteristic frequency, the anti-resonance of soliton oscillation can be found. In addition, it is found that the characteristic driven frequency increases linearly with the increase of the trapping frequency of the harmonic potential. When the initial phase is not equal to zero, the irregular oscillation, quasi-periodic oscillation, and periodic oscillation can be observed with the increase of driven frequency. When the driven frequency is equal to a specific value, the resonance of soliton oscillation can also obtained. Furthermore, the fast driving has no effect on the motion trajectory of solitons. These results can help to precisely control ultracold atomic gases.

Patricia Daukantas

Sinisa Coh

Takahiro Orito, Yoshihito Kuno, Ikuo Ichinose

In this work, we construct an exact projector Hamiltonian with interactions, which is given by a sum of mutually commuting operators called stabilizers. The model is based on the recently studied Creutz ladder of fermions, in which flat-band structure and strong localization are realized. These stabilizers are local integrals of motion from which many-body localization (MBL) is realized. All energy eigenstates are explicitly obtained even in the presence of local disorders. All states are MBL states, that is, this system is a full many-body localized (FMBL) system. We show that this system has a topological order and stable gapless edge modes exist under the open boundary condition. By the numerical study, we investigate stability of the FMBL and topological order.