We work out the theory and applications of a fast quasiadiabatic approach to speed up slow adiabatic manipulations of quantum systems by driving a control parameter as near to the adiabatic limit as possible over the entire protocol duration. We find characteristic time scales, such as the minimal time to achieve fidelity 1, and the optimality of the approach within the iterative superadiabatic sequence. Specifically, we show that the population inversion in a two-level system, the splitting and cotunneling of two-interacting bosons, and the stirring of a Tonks-Girardeau gas on a ring to achieve mesoscopic superpositions of many-body rotating and nonrotating states can be significantly speeded up

We report a model that makes it possible to analyze quantitatively the dipole blockade effect on the dynamical evolution of a two two-level atom system driven by an external laser field. The multiple excitations of the atomic sample are taken into account. We find very large concurrence in the dipole blockade regime. We further find that entanglement can be tuned by changing the intensity of the exciting laser. We also report a way to lift the dipole blockade paving the way to manipulate in a controllable way the blockade effects. We finally report how a continuous monitoring of the dipole blockade would be possible using photon-photon correlations of the scattered light in a regime where the spontaneous emission would dominate dissipation in the sample.

We consider an atomic Bose-Einstein condensate trapped in a symmetric one-dimensional double-well potential in the four-mode approximation and show that the semiclassical dynamics of the two ground-state modes can be strongly influenced by a macroscopic occupation of the two excited modes. In particular, the addition of the two excited modes already unveils features related to the effect of dissipation on the condensate. In general, we find a rich dynamics that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping, chaotic behavior, and the existence of fixed points. We investigate how the dynamics of the atoms in the excited modes can be manipulated by controlling the atomic populations of the ground states.

We formulate an entanglement criterion using Peres-Horodecki positive partial transpose operations combined with the Schrödinger-Robertson uncertainty relation. We show that any pure entangled bipartite and tripartite state can be detected by experimentally measuring mean values and variances of specific observables. Those observables must satisfy a specific condition in order to be used, and we show their general form in the 2 × 2 (two qubits) dimension case. The criterion is applied on a variety of physical systems including bipartite and multipartite mixed states and reveals itself to be stronger than the Bell inequalities and other criteria. The criterion also work on continuous variable cat states and angular momentum states of the radiation field.PACS numbers: 03.65. Ud, 03.67.Mn In the past few years, many criteria detecting entanglement in bipartite and multipartite systems have been developed [1]. The Peres-Horodecki positive partial transpose (PPT) criterion [2] has played a crucial role in the field and provides, in some cases, necessary and sufficient conditions to entanglement. That criteria is formulated in terms of the density operator and any practical application involves state tomography. Other criteria have been proposed so they could be tested experimentally in a direct manner, as the Bell inequalities [3,4] or the entanglement witnesses [5]. More recently, criteria based on variance measurements have been studied for continuous and discrete variable systems [6,7,8,9,10,11,12,13,14].In [11] the Heisenberg relation has been used along with the partial transpose operation to obtain a criterion detecting entanglement condition in bipartite nongaussian states. That idea was generalized in [13,14] with use of the Schrödinger-Robertson relation instead of the Heisenberg inequality. In this paper, we generalize completely those concepts and prove that the Schrödinger-Robertson type inequality is able to detect entanglement in any pure state of bipartite and tripartite systems. Experimentally, it can be realized by measuring mean values and variances of different observables; however we show that all observables are not suitable and we yield the general condition they must satisfy to be eligible. For 2 × 2 systems, we explicitly give their general form. The inequality has a wide application range : qubits, angular momentum states of harmonic oscillators, cat states, etc. For the mixed state case, the inequality detects entanglement of bipartite Werner states better than the Bell inequalities [3] and also leads to a good characterization of multipartite Werner states.For any observables A, B and any density operator ρ, the Schrödinger-Robertson uncertainty relation The Heisenberg uncertainty relation is obtained if the last term is not considered, which gives a weaker inequality.The PPT criterion [2] is a sufficient condition for entanglement, saying that if a bipartite state ρ is separable it can be written as ρ = i p i ρ 1 i ⊗ ρ 2 i with usual notations and its partial transpose ρ pt ≡ i p i ρ 1 ...