Facultades y Escuela Politécnica Superior
http://hdl.handle.net/10486/129087
2019-08-24T02:29:15ZStrong coupling between weakly guided semiconductor nanowire modes and an organic dye
http://hdl.handle.net/10486/688404
Strong coupling between weakly guided semiconductor nanowire modes and an organic dye
Abujetas, Diego R.; Feist, Johannes; García-Vidal, Francisco J.; Rivas, Jaime Gómez; Sánchez-Gil, José A.
The light-matter coupling between electromagnetic modes guided by a semiconductor nanowire and excitonic states of molecules localized in its surrounding media is studied from both classical and quantum perspectives, with the aim of describing the strong-coupling regime. Weakly guided modes (bare photonic modes) are found through a classical analysis, identifying those lowest-order modes presenting large electromagnetic fields spreading outside the nanowire while preserving their robust guided behavior. Experimental fits of the dielectric permittivity of an organic dye that exhibits excitonic states are used for realistic scenarios. A quantum model properly confirms through an avoided mode crossing that the strong-coupling regime can be achieved for this configuration, leading to Rabi splitting values above 100 meV. In addition, it is shown that the coupling strength depends on the fraction of energy spread outside the nanowire, rather than on the mode field localization. These results open up a new avenue towards strong-coupling phenomenology involving propagating modes in nonabsorbing media.
2019-05-09T00:00:00ZPolarization tagging of two-photon double ionization by elliptically polarized XUV pulses
http://hdl.handle.net/10486/688403
Polarization tagging of two-photon double ionization by elliptically polarized XUV pulses
Donsa, Stefan; Březinová, Iva; Ni, Hongcheng; Feist, Johannes; Burgdörfer, Joachim
We explore the influence of elliptical polarization on the (non)sequential two-photon double ionization of atomic helium with ultrashort extreme ultraviolet (XUV) light fields using time-dependent full ab initio simulations. The energy and angular distributions of photoelectrons are found to be strongly dependent on the ellipticity. The correlation minimum in the joint angular distribution becomes more prominently visible with increasing ellipticity. In a pump-probe sequence of two subsequent XUV pulses with varying ellipticities, polarization tagging allows us to discriminate between sequential and nonsequential photoionization. This clear separation demonstrates the potential of elliptically polarized XUV fields for improved control of electronic emission processes.
2019-02-11T00:00:00ZFiltered gradient algorithms for inverse design problems of one-dimensional burgers equation
http://hdl.handle.net/10486/688402
Filtered gradient algorithms for inverse design problems of one-dimensional burgers equation
Gosse, Laurent; Zuazua, Enrique
Gosse, Laurent; Natalini, Roberto
Inverse design for hyperbolic conservation laws is exemplified through the 1D Burgers equation which is motivated by aircraft’s sonic-boom minimization issues. In particular, we prove that, as soon as the target function (usually a Nwave) isn’t continuous, there is a whole convex set of possible initial data, the backward entropy solution being possibly its centroid. Further, an iterative strategy based on a gradient algorithm involving “reversible solutions” solving the linear adjoint problem is set up. In order to be able to recover initial profiles different from the backward entropy solution, a filtering step of the backward adjoint solution is inserted, mostly relying on scale-limited (wavelet) subspaces. Numerical illustrations, along with profiles similar to F-functions, are presented
The final publication is available at Springer via https://doi.org/10.1007/978-3-319-49262-9_7
2017-03-09T00:00:00ZCavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity
http://hdl.handle.net/10486/688401
Cavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity
Galego, Javier; Climent, Clàudia; Garcia-Vidal, Francisco J.; Feist, Johannes
Here, we present a fundamental study on how the ground-state chemical reactivity of a single molecule can be modified in a QED scenario, i.e., when it is placed inside a nanoscale cavity and there is strong coupling between the cavity field and vibrational modes within the molecule. We work with a model system for the molecule (Shin-Metiu model) in which nuclear, electronic, and photonic degrees of freedom are treated on the same footing. This simplified model allows the comparison of exact quantum reaction rate calculations with predictions emerging from transition state theory based on the cavity Born-Oppenheimer approach. We demonstrate that QED effects are indeed able to significantly modify activation barriers in chemical reactions and, as a consequence, reaction rates. The critical physical parameter controlling this effect is the permanent dipole of the molecule and how this magnitude changes along the reaction coordinate. We show that the effective coupling can lead to significant single-molecule energy shifts in an experimentally available nanoparticle-on-mirror cavity. We then apply the validated theory to a realistic case (internal rotation in the 1,2-dichloroethane molecule), showing how reactions can be inhibited or catalyzed depending on the profile of the molecular dipole. Furthermore, we discuss the absence of resonance effects in the present scenario, which can be understood through its connection to Casimir-Polder forces. Finally, we treat the case of many-molecule strong coupling and find collective modifications of reaction rates if the molecular permanent dipole moments are oriented with respect to the cavity field
2019-06-21T00:00:00Z