Controlling the phase of a light beam with a single molecule

We employ heterodyne interferometry to investigate the effect of a single organic molecule on the phase of a propagating laser beam. We report on the first phase-contrast images of individual molecules and demonstrate a single-molecule electro-optical phase switch by applying a voltage to the microelectrodes embedded in the sample. Our results may find applications in single-molecule holography, fast optical coherent signal processing, and single-emitter quantum operations

Effects of ligands on (de-)enhancement of plasmonic excitations of silver, gold and bimetallic nanoclusters: TD-DFT+TB calculations

Metal nanoclusters can be synthesized in various sizes and shapes and are typically protected with ligands to stabilize them. These ligands can also be used to tune the plasmonic properties of the clusters as the absorption spectrum of a protected cluster can be significantly altered compared to the bare cluster. In this paper, we computationally investigate the influence of thiolate ligands on the plasmonic intensity for silver, gold and alloy clusters. Using time-dependent density functional theory with tight-binding approximations, TD-DFT+TB, we show that this level of theory can reproduce the broad experimental spectra of Au144(SR)60 and Ag53Au91(SR)60 (R = CH3) compounds with satisfactory agreement. As TD-DFT+TB does not depend on atom-type parameters we were able to apply this approach on large ligand-protected clusters with various compositions. With these calculations we predict that the effect of ligands on the absorption can be a quenching as well as an enhancement. We furthermore show that it is possible to unambiguously identify the plasmonic peaks by the scaled Coulomb kernel technique and explain the influence of ligands on the intensity (de-)enhancement by analyzing the plasmonic excitations in terms of the dominant orbital contributions

RYDBERG STATES OF ALKALI METAL ATOMS ON SUPERFLUID HELIUM DROPLETS - THEORETICAL CONSIDERATIONS

The bound states of electrons on the surface of superfluid helium have been a research topic for several decades. One of the first systems treated was an electron bound to an ionized helium cluster.footnote{A. Golov and S. Sekatskii, Physica B, 1994, 194, 555-556} Here, a similar system is considered, which consists of a helium droplet with an ionized dopant inside and an orbiting electron on the outside. In our theoretical investigation we select alkali metal atoms (AK) as central ions, stimulated by recent experimental studies of Rydberg states for Na,footnote{E. Loginov, C. Callegari, F. Ancilotto, and M. Drabbels, J. Phys. Chem. A, 2011, 115, 6779-6788} Rb,footnote{F. Lackner, G. Krois, M. Koch, and W. E. Ernst, J. Phys. Chem. Lett., 2012, 3, 1404-1408} and Csfootnote{F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys., 2011, 13, 18781-18788} attached to superfluid helium nanodroplets. Experimental spectra , obtained by electronic excitation and subsequent ionization, showed blueshifts for low lying electronic states and redshifts for Rydberg states._x000d_ _x000d_ In our theoretical treatment the diatomic AK$^+$-He potential energy curves are first computed with textit{ab initio} methods. These potentials are then used to calculate the solvation energy of the ion in a helium droplet as a function of the number of atoms. Additional potential terms, derived from the obtained helium density distribution, are added to the undisturbed atomic pseudopotential in order to simulate a 'modified' potential felt by the outermost electron. This allows us to compute a new set of eigenstates and eigenenergies, which we compare to the experimentally observed energy shifts for highly excited alkali metal atoms on helium nanodroplets._x000d

Securing Gas for Europe : (a follow up to the policy brief on capping the European price of gas)

The imposition of a cap on the price of gas traded in the EU is increasingly the focus of the policy debate in Europe. In a previous Policy Brief, we outlined a possible approach to contain the price of gas in the EU, while safeguarding security of supply as much as possible. In this Policy Brief we explore two aspects related to the measures outlined in the previous one: (i) How would the gas imported as LNG by the TSOs or the Single Buyer entity be allocated to the different TSOs/Member States? (ii) How would the additional costs of importing LNG with respect to the price cap for pipeline gas in the EU be recovered? In the proposed mechanism, the gas volumes to be procured through the LNG auctions would be determined by aggregating the requests of the different TSOs. Therefore, at least as a first approximation, the allocations of the procured LNG volumes to the different TSOs could be based on their respective requests. We also explore additional aspects which would need to be considered if we move beyond this first approximation. We also propose that the additional costs of importing LNG with respect to the price cap for pipeline gas in the EU be recovered through an uplift charged on final consumption. We propose different approaches in terms of uplift levels and the base on which it is charged and we compare them with respect to two criteria: revenue adequacy and the ability to provide the correct price signals to consumers to promote efficient demand reduction