ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

loss hollow core fiber, amenable to be filled with a gas sample. The high degree of light confinement together witha longer interaction length has led to the conception of a new experimental configuration to carry out high resolutionRaman spectroscopy without pulsed lasers.Finally, we have observed the first Raman signals with an spectralresolution better than 0.006 cm -1 and a remarkable signal to noise ratio in the ν 1 band of CO 2 at 100 kPa.THEORETICAL MOLECULAR PHYSICSMolecular Quantum Control. Molecular alignment and orientationWe have studied the control of alignment and orientation of polar molecules in optical lattices, using a combinationof static electric field and a pulse train of non-resonant laser pulses. Long-range dipolar interaction strongly affectsthe macroscopic properties of a quantum gas and this field is very active. The control of the orientation of moleculardipoles provides a handle to control these macroscopic properties.A very important application of this system is quantum computing. We have found that the inclusion of nonresonantlaser pulses allows controlling the entanglement of dipolar molecules in an optical lattice.For isolated molecules, we have carried on the study of cyclic states for potentials HCP (Half-Cycle Pulse). Thoseintrinsically asymmetric potentials allow for the direct orientation of dipolar molecules and the cyclic states can becreated and controlled adiabatically under appropriate evolution of the control field.Control of the torsional angles of nonrigid molecules is key for the development of emerging areas like molecularelectronics and nanotechnology. Based on a rigorous calculation of the rotation-torsion-Stark energy levels ofnonrigid biphenyl-like molecules, we have shown that, unlike previously believed, instantaneous rotation-torsion-Stark eigenstates of such molecules, interacting with a strong laser field, present a large degree of delocalization inthe torsional coordinate even for the lowest energy states. Thus, we have shown that adiabatic control of changes onthe planarity of this kind of molecule is essentially impossible unless the temperature is on the order of a few Kelvin.We have also continued the study of energy transfer in light-harvesting complexes (LHC) and the importance ofquantum coherence and the back-action of the molecular environment on the energy flow. We have used an excitonmodel for the energy transfer and calculated the energy-transfer efficiency and the trapping time for the Fenna-Matthews-Olson complex. We have used the model to interpret two-dimensional echo-spectra of this complex. Thiswork has been done in collaboration with the group of Tobias Kramer from the University of Regensburg.Ultracold Quantum gasesWe have studied the momentum generation in a system of atoms at rest in an optical lattice, modulating thelatticewith an unbiased time and spatially periodic laser field. . Generation of an asymptotic current at infinite timeis only possible when both time and spatial symmetry of the system are broken. Our work shows that by using atailored potential that does not break time-reversal symmetry it is still possible to maintain a relevant net averagecurrent in a time scale that can be fitted to the lifetime of actual experiments. Our model has proven to be bothhighly controllable and robust. We have studied the effect of particle interaction on this model, and found that apulsed modulation of the interaction parameter can create and control a persistent current.We have carried on the study of the use of atom counting as a tool to distinguish strongly correlated phasesofultracold atoms, both for bosons and fermions, in collaboration with the group of Prof. M. Lewenstein fromInstituto de Ciencias Fotónicas.2B.4 MACROMOLECULAR PHYSICS DEPARTMENTRESEARCH LINES:‣ Simulation of polymer reactions and of physical properties of polymers.‣ Physical properties and nanostructure of polymers.‣ Polymer Physics: Order and mobility in macromolecular systems.‣ Application of the synchrotron light to the study of polymers and nanostructured materials.‣ Interfaces.RESEARCH SUBLINES:71