Three-level atom optics is introduced as a simple, efficient, and robust method to coherently manipulate and transport neutral atoms. The tunneling interaction among three trapped states allows us to realize the spatial analog of the stimulated Raman adiabatic passage, coherent population trapping, and electromagnetically induced transparency techniques and offers a wide range of possible applications. We investigate an implementation in optical microtrap arrays and show that under realistic parameters the coherent manipulation and transfer of neutral atoms among dipole traps could be realized in the millisecond range.

Abstract. Bohmian mechanics provides an explanation of quantum phenomena in terms of point-like particles guided by wave functions. This review focuses on the use of nonrelativistic Bohmian mechanics to address practical problems, rather than on its interpretation. Although the Bohmian and standard quantum theories have different formalisms, both give exactly the same predictions for all phenomena. Fifteen years ago, the quantum chemistry community began to study the practical usefulness of Bohmian mechanics. Since then, the scientific community has mainly applied it to study the (unitary) evolution of single-particle wave functions, either by developing efficient quantum trajectory algorithms or by providing a trajectorybased explanation of complicated quantum phenomena. Here we present a large list of examples showing how the Bohmian formalism provides a useful solution in different forefront research fields for this kind of problems (where the Bohmian and the quantum hydrodynamic formalisms coincide). In addition, this work also emphasizes that the Bohmian formalism can be a useful tool in other types of (nonunitary and nonlinear) quantum problems where the influence of the environment or the nonsimulated degrees of freedom are relevant. This review contains also examples on the use of the Bohmian formalism for the many-body problem, decoherence and measurement processes. The ability of the Bohmian formalism to analyze this last type of problems for (open) quantum systems remains mainly unexplored by the scientific community. The authors of this review are convinced that the final status of the Bohmian theory among the scientific community will be greatly influenced by its potential success in those types of problems that present nonunitary and/or nonlinear quantum evolutions. A brief introduction of the Bohmian formalism and some of its extensions are presented in the last part of this review.

This review paper is devoted to amplification and lasing without population inversion involving atomic transitions in gas media. We start by discussing the main motivation in inversionless lasing research, namely, the generation of short-wavelength laser light. Then, we review the basic physics of inversionless lasing in two-level and, eventually, in three-and multilevel atomic configurations. Finally, we summarize the current state of the art of LWI experiments and indicate the main difficulties with respect to short-wavelength laser generation.

Light beams carrying orbital angular momentum, such as Laguerre-Gaussian beams, give rise to the violation of the standard dipolar selection rules during the interaction with matter yielding, in general, an exchange of angular momentum larger thanh per absorbed photon. By means of ab initio 3D numerical simulations, we investigate in detail the interaction of a hydrogen atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the dependence of the angular momentum exchange with the polarization, the orbital angular momentum, and the carrier-envelope phase of light, as well as with the relative position between the atom and the light vortex. In addition, a quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum mechanics is used to gain physical insight into the absorption of angular momentum by the hydrogen atom.

We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multi-qubit highly entangled states can be created in this scheme.PACS . Some remarkable characteristics of optical microtraps are the possibility to scale, miniaturize and parallelize the required atom optics devices. In addition, they offer two fundamental advantages over optical lattices: (i) the possibility of individually addressing single traps due to the large separation of the microlenses foci, e.g., ∼ 125µm; and (ii) the independent displacement of rows and columns of microtraps and, eventually, of single microtraps. Single atoms in dipole traps [3] and the Mott insulator transition with one atom per trap in optical lattices [4] have been reported, and, therefore, the achievement of 1D and 2D arrays of optical microtraps containing none or one atom per trap in a deterministic way can be foreseen for the near future. We will make use of all these features of optical microtraps to propose a novel implementation for quantum information processing.In our scheme, each qubit consists of two traps separated by a distance 2a and one single atom. Per definition, the detection of the atom in the ground state of the left trap represents |0 and in the right trap |1 , i.e., |0 = |0 L and |1 = |0 R , where |0 L,R are the vibrational ground states of the left and right trap, respectively. Throughout the paper we will call this implementation the spatially delocalized qubit (SDQ), since | 0| r|0 − 1| r|1 | = 2a with r the position operator. To implement the SDQ we will assume that we are able to deterministically store none or one single atom per trap and cool it to the vibrational ground state in 3D.Single and two-qubit gate operations will be performed by adiabatically approaching two traps which will be modeled as follows: The initial separation of the traps is 2a max . The process of approaching them to the minimum separation 2a min takes a raising time t r . The temporal evolution of the distance a is described by the first half of a period of a cosine. The two wells remain at the minimum separation for an interaction time t i and, finally, are adiabatically separated to the initial distance.To simplify the numerical analysis we will assume piecewise harmonic trapping potentials as in ref.[5] and, eventually, consider realistic Gaussian potentials as they are present in the experiment [2,6].Single-qubit operations, e.g., a Hadamard gate, are performed by adiabatically approaching the traps and allowing tunneling to take place. In order to illustrate this operation, it is convenient to consider the two lowest energy eigenstates of the double well potential. These ...