%0 Journal Article
%J Nature Photonics
%D 2019
%T Knotting fractional-order knots with the polarization state of light
%A E. Pisanty
%A G. J. Machado
%A V. Vicuña-Hernández
%A A. Picón
%A A. Celi
%A J. P. Torres
%A M. Lewenstein
%X The fundamental polarization singularities of monochromatic light are normally associated with invariance under coordinated rotations: symmetry operations that rotate the spatial dependence of an electromagnetic field by an angle *θ* and its polarization by a multiple *γθ* of that angle. These symmetries are generated by mixed angular momenta of the form *J*_{γ} = *L* + *γS*, and they generally induce Möbius-strip topologies, with the coordination parameter *γ* restricted to integer and half-integer values. In this work we construct beams of light that are invariant under coordinated rotations for arbitrary rational *γ*, by exploiting the higher internal symmetry of ‘bicircular’ superpositions of counter-rotating circularly polarized beams at different frequencies. We show that these beams have the topology of a torus knot, which reflects the subgroup generated by the torus-knot angular momentum *J*_{γ}, and we characterize the resulting optical polarization singularity using third- and higher-order field moment tensors, which we experimentally observe using nonlinear polarization tomography.

%B Nature Photonics
%V 13
%U https://www.nature.com/articles/s41566-019-0450-2
%& 569
%R https://doi.org/10.5281/zenodo.2649391
%0 Journal Article
%J New Journal of Physics
%D 2015
%T Stimulated Raman adiabatic passage with two-color x-ray pulses
%A A. Picón
%A J. Mompart
%A S. H Southworth
%X Recent techniques in x-ray free electron lasers allow the generation of highly coherent, intense x-ray pulses with time lengths on the order of femtoseconds. Here we explore the possibilities of using such x-ray pulses to control matter based on coherence. In particular we propose a theoretical scheme to perform stimulated Raman adiabatic passage in the x-ray regime by using inner-hole excited states. Numerical results in two well-known systems, the neon atom and the carbon monoxide molecule, show a robust control of population transfer. In the molecule, vibrational selectivity is achieved with femtosecond x-ray pulses. This work supports the possibility of using two-color x-ray pulses for coherent control.
%B New Journal of Physics
%V 17
%P 083038
%U http://stacks.iop.org/1367-2630/17/i=8/a=083038
%0 Journal Article
%J Journal of Optics
%D 2011
%T Spin and orbital angular momentum propagation in anisotropic media: theory
%A A. Picón
%A A. Benseny
%A J. Mompart
%A G F Calvo
%X This paper is devoted to a study of the propagation of light beams carrying orbital angular momentum in optically anisotropic media. We first review some properties of homogeneous anisotropic media, and describe how the paraxial formalism is modified in order to proceed with a new approach dealing with the general setting of paraxial propagation along uniaxial inhomogeneous media. This approach is suitable for describing space-variant optical-axis phase plates.
%B Journal of Optics
%V 13
%P 064019
%U http://stacks.iop.org/2040-8986/13/i=6/a=064019
%0 Journal Article
%J Phys. Rev. A
%D 2010
%T Atomtronics with holes: Coherent transport of an empty site in a triple-well potential
%A A. Benseny
%A S. Fernández-Vidal
%A J. Bagudà
%A R. Corbalán
%A A. Picón
%A L. Roso
%A G. Birkl
%A J. Mompart
%X We investigate arrays of three traps with two fermionic or bosonic atoms. The tunneling interaction between neighboring sites is used to prepare multisite dark states for the empty site (i.e., the hole) which allows for the coherent manipulation of its external degrees of freedom. By means of an ab initio integration of the Schrödinger equation, we investigate the adiabatic transport of a hole between the two extreme traps of a triple-well potential. Furthermore, a quantum-trajectory approach based on the de Broglie–Bohm formulation of quantum mechanics is used to get physical insight into the transport process. Finally, we discuss the use of the hole for the construction of a coherent single hole diode and a coherent single hole transistor.
%B Phys. Rev. A
%I American Physical Society
%V 82
%P 013604
%8 Jul
%U http://link.aps.org/doi/10.1103/PhysRevA.82.013604
%R 10.1103/PhysRevA.82.013604
%0 Journal Article
%J Phys. Rev. A
%D 2010
%T Dipole spectrum structure of nonresonant nonpertubative driven two-level atoms
%A A. Picón
%A L. Roso
%A J. Mompart
%A O. Varela
%A V. Ahufinger
%A R. Corbalán
%A L. Plaja
%X We analyze the dipole spectrum of a two-level atom excited by a nonresonant intense monochromatic field under the electric dipole approximation and beyond the rotating wave approximation. We show that the apparently complex spectral structure can be completely described by two families: harmonic frequencies of the driving field and field-induced nonlinear fluorescence. Our formulation of the problem provides quantitative laws for the most relevant spectral features: harmonic ratios and phases, nonperturbative Stark shift, and frequency limits of the harmonic plateau. In particular, we demonstrate the locking of the harmonic phases at the wings of the plateau opening the possibility of ultrashort pulse generation through harmonic filtering.
%B Phys. Rev. A
%I American Physical Society
%V 81
%P 033420
%8 Mar
%U http://link.aps.org/doi/10.1103/PhysRevA.81.033420
%R 10.1103/PhysRevA.81.033420
%0 Journal Article
%J New Journal of Physics
%D 2010
%T Transferring orbital and spin angular momenta of light to atoms
%A A. Picón
%A A. Benseny
%A J. Mompart
%A J R Vázquez de Aldana
%A L. Plaja
%A G F Calvo
%A L. Roso
%X Light beams carrying orbital angular momentum (OAM), such as Laguerre–Gaussian (LG) beams, give rise to the violation of the standard dipolar selection rules during interaction with matter, yielding, in general, an exchange of angular momentum larger than ##IMG## [http://ej.iop.org/icons/Entities/planck.gif] {planck} per absorbed photon. By means of ab initio three-dimensional (3D) numerical simulations, we investigate in detail the interaction of a hydrogen atom with intense Gaussian and LG light pulses. We analyze the dependence of the angular momentum exchange with the polarization, the OAM 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.
%B New Journal of Physics
%V 12
%P 083053
%U http://stacks.iop.org/1367-2630/12/i=8/a=083053