Periodically-driven quantum systems: Effective Hamiltonians and engineered gauge fields

Driving a quantum system periodically in time can profoundly alter its long-time dynamics and trigger topological order. Such schemes are particularly promising for generating non-trivial energy bands and gauge structures in quantum-matter systems. Here, we develop a general formalism that captures the essential features ruling the dynamics: the effective Hamiltonian, but also the effects related to the initial phase of the modulation and the micro-motion. This framework allows for the identification of driving schemes, based on general N-step modulations, which lead to configurations relevant for quantum simulation. In particular, we explore methods to generate synthetic spin-orbit couplings and magnetic fields in cold-atom setups.Comment: 25 pages, 6 figures, includes Appendices (A-K). An erroneous factor of two has been corrected in the last term of Eq. C10 (Appendix C); this typo had no impact on the rest of the articl

All-optical production of 7Li Bose-Einstein condensation using Feshbach resonances

We show an all-optical method of making 7Li condensate using tunability of the scattering length in the proximity of a Feshbach resonance. We report the observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow (broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G). Position of the scattering length zero crossing between the resonances is found at 836 +- 4 G. The broad resonance is shown to be favorable for run away evaporation which we perform in a crossed-beam optical dipole trap. Starting directly form the phase space density of a magneto-optical trap we observe a Bose-Einstein condensation threshold in less than 3 s of forced evaporation.Comment: 5 pages, 5 figure

Spontaneous excitation of an accelerated hydrogen atom coupled with electromagnetic vacuum fluctuations

We consider a multilevel hydrogen atom in interaction with the quantum electromagnetic field and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy of the atom for uniform acceleration. It is found that the acceleration disturbs the vacuum fluctuations in such a way that the delicate balance between the contributions of vacuum fluctuation and radiation reaction that exists for inertial atoms is broken, so that the transitions to higher-lying states from ground state are possible even in vacuum. In contrast to the case of an atom interacting with a scalar field, the contributions of both electromagnetic vacuum fluctuations and radiation reaction to the spontaneous emission rate are affected by the acceleration, and furthermore the contribution of the vacuum fluctuations contains a non-thermal acceleration-dependent correction, which is possibly observable.Comment: 8 pages, Revtex4, accepted for publication in PR

Modification of energy shifts of atoms by the presence of a boundary in a thermal bath and the Casimir-Polder force

We study the modification by the presence of a plane wall of energy level shifts of two-level atoms which are in multipolar coupling with quantized electromagnetic fields in a thermal bath in a formalism which separates the contributions of thermal fluctuations and radiation reaction and allows a distinct treatment to atoms in the ground and excited states. The position dependent energy shifts give rise to an induced force acting on the atoms. We are able to identify three different regimes where the force shows distinct features and examine, in all regimes, the behaviors of this force in both the low temperature limit and the high temperature limit for both the ground state and excited state atoms, thus providing some physical insights into the atom-wall interaction at finite temperature. In particular, we show that both the magnitude and the direction of the force acting on an atom may have a clear dependence on atomic the polarization directions. In certain cases, a change of relative ratio of polarizations in different directions may result in a change of direction of the force.Comment: 29 pages, 3 figure

Spontaneous excitation of an accelerated multilevel atom in dipole coupling to the derivative of a scalar field

We study the spontaneous excitation of an accelerated multilevel atom in dipole coupling to the derivative of a massless quantum scalar field and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy of the atom. It is found that, in contrast to the case where a monopole like interaction between the atom and the field is assumed, there appear extra corrections proportional to the acceleration squared, in addition to corrections which can be viewed as a result of an ambient thermal bath at the Unruh temperature, as compared with the inertial case, and the acceleration induced correction terms show anisotropy with the contribution from longitudinal polarization being four times that from the transverse polarization for isotropically polarized accelerated atoms. Our results suggest that the effect of acceleration on the rate of change of the mean atomic energy is dependent not only on the quantum field to which the atom is coupled, but also on the type of the interaction even if the same quantum scalar field is considered.Comment: 11 pages, no figure

Vortex formation in a stirred Bose-Einstein condensate

Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb confined in a magnetic trap and observe the formation of a vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to four vortices are simultaneously present. We have also measured the lifetime of the single vortex state after turning off the stirring laser beam.Comment: 4 pages, 3 figure

Spontaneous absorption of an accelerated hydrogen atom near a conducting plane in vacuum

We study, in the multipolar coupling scheme, a uniformly accelerated multilevel hydrogen atom in interaction with the quantum electromagnetic field near a conducting boundary and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy. It is found that the perfect balance between the contributions of vacuum fluctuations and radiation reaction that ensures the stability of ground-state atoms is disturbed, making spontaneous transition of ground-state atoms to excited states possible in vacuum with a conducting boundary. The boundary-induced contribution is effectively a nonthermal correction, which enhances or weakens the nonthermal effect already present in the unbounded case, thus possibly making the effect easier to observe. An interesting feature worth being noted is that the nonthermal corrections may vanish for atoms on some particular trajectories.Comment: 19 pages, no figures, Revtex