Päivi Törmä

Strong coupling between surface plasmon polaritons and emitters: a review

In this review we look at the concepts and state-of-the-art concerning the strong coupling of surface plasmon-polariton modes to states associated with quantum emitters such as excitons in J-aggregates, dye molecules and quantum dots. We explore the phenomenon of strong coupling with reference to a number of examples involving electromagnetic fields and matter. We then provide a concise description of the relevant background physics of surface plasmon polaritons. An extensive overview of the historical background and a detailed discussion of more recent relevant experimental advances concerning strong coupling between surface plasmon polaritons and quantum emitters is then presented. Three conceptual frameworks are then discussed and compared in depth: classical, semi-classical and fully quantum mechanical; these theoretical frameworks will have relevance to strong coupling beyond that involving surface plasmon polaritons. We conclude our review with a perspective on the future of this rapidly emerging field, one we are sure will grow to encompass more intriguing physics and will develop in scope to be of relevance to other areas of science.

Vortices in Trapped Superfluid Fermi Gases

We consider a superfluid of trapped fermionic atoms and study the single vortex solution in the Ginzburg-Landau regime. We define simple analytical estimates for the main characteristics of the system, such as the vortex core size, temperature regimes for the existence of a vortex, and the effects of rotation and interactions with normal fermions. The parameter dependence of the vortex core size (healing length) is found to be essentially different from that of the healing length in metallic superconductors or in trapped atomic Bose-Einstein condensation in the Thomas-Fermi limit. This is an indication of the importance of the confining geometry for the properties of fermionic superfluids.

Vacuum rabi splitting and strong-coupling dynamics for surface-plasmon polaritons and rhodamine 6G molecules

We report on strong coupling between surface-plasmon polaritons (SPP) and Rhodamine 6G (R6G) molecules, with double vacuum Rabi splitting energies up to 230 and 110 meV. In addition, we demonstrate the emission of all three energy branches of the strongly coupled SPP-exciton hybrid system, revealing features of system dynamics that are not visible in conventional reflectometry. Finally, in analogy to tunable-Q microcavities, we show that the Rabi splitting can be controlled by adjusting the interaction time between waveguided SPPs and R6G deposited on top of the waveguide. The interaction time can be controlled with sub-fs precision by adjusting the length of the R6G area with standard lithography methods.

Optimization of dual-core and microstructure fiber geometries for dispersion compensation and large mode area

We investigate dual concentric core and microstructure fiber geometries for dispersion compensation. Dispersion values as large as -59 000 ps/(nm km) are achieved, over a broad wavelength range with full width at half maximum exceeding 100 nm. The trade-off between large dispersion and mode area is studied. Geometries with an effective mode area of 30 microm2 and dispersion -19 000 ps/(nm km) and 80 microm2 with -1600 ps/(nm km) are proposed.

Plasmonic Surface Lattice Resonances at the Strong Coupling Regime

We show strong coupling involving three different types of resonances in plasmonic nanoarrays: surface lattice resonances (SLRs), localized surface plasmon resonances on single nanoparticles, and excitations of organic dye molecules. The measured transmission spectra show splittings that depend on the molecule concentration. The results are analyzed using finite-difference time-domain simulations, a coupled-dipole approximation, coupled-modes models, and Fano theory. The delocalized nature of the collective SLR modes suggests that in the strong coupling regime molecules near distant nanoparticles are coherently coupled.

Virus-Encapsulated DNA Origami Nanostructures for Cellular Delivery

DNA origami structures can be programmed into arbitrary shapes with nanometer scale precision, which opens up numerous attractive opportunities to engineer novel functional materials. One intriguing possibility is to use DNA origamis for fully tunable, targeted, and triggered drug delivery. In this work, we demonstrate the coating of DNA origami nanostructures with virus capsid proteins for enhancing cellular delivery. Our approach utilizes purified cowpea chlorotic mottle virus capsid proteins that can bind and self-assemble on the origami surface through electrostatic interactions and further pack the origami nanostructures inside the viral capsid. Confocal microscopy imaging and transfection studies with a human HEK293 cell line indicate that protein coating improves cellular attachment and delivery of origamis into the cells by 13-fold compared to bare DNA origamis. The presented method could readily find applications not only in sophisticated drug delivery applications but also in organizing intracellular reactions by origami-based templates.

Dielectrophoretic Trapping of DNA Origami

In this thesis three-dimensional tube-shaped DNA-origamis were dielectrophoretically trapped within lithographically fabricated nanoelectrodes. The origamis had been premade while the electrodes were fabricated specifically for these experiments with two different gapsizes, 150 nm and 400 nm. The aim of the work was to capture individual nanotubes in the gap between the electrodes by utilizing the dielectrophoretic forces present in the structure when a solution containing the origamis was put onto the electrodes and a voltage was applied. It was observed during the experiments that the success of the dielectrophoretic trapping depended strongly on the trapping conditions. This caused the trapping to be somewhat challenging and it was also noticed that the electrode structure with the 400 nm gap particularly required patience in order to produce good results, since the origamis to be trapped were of the same size as the gap between the electrodes making the successful trapping problematic. Despite this, a sufficient amount of trapped single nanotubes were produced.

DNA origami as a nanoscale template for protein assembly.

We describe two general approaches to the utilization of DNA origami structures for the assembly of materials. In one approach, DNA origami is used as a prefabricated template for subsequent assembly of materials. In the other, materials are assembled simultaneously with the DNA origami, i.e. the DNA origami technique is used to drive the assembly of materials. Fabrication of complex protein structures is demonstrated by these two approaches. The latter approach has the potential to be extended to the assembly of multiple materials with single attachment chemistry.

Approximate Quantum Fourier Transform and Decoherence

AbstractWe discuss the advantages of using the approximate quantum Fourier trans-form (AQFT) in algorithms which involve periodicity estimations. We analysequantum networks performing AQFT in the presence of decoherence and showthat extensive approximations can be made before the accuracy of AQFT (ascompared with regular quantum Fourier transform) is compromised. We showthat for some computations an approximation may imply a better performance.PACS: 89.70.+c, 03.65.-w, 42.50.Lc Submitted to Phys. Rev. A. (Jan. 96) 1 Introduction In the course of history many ingenious mechanical, acoustic and optical devices havebeen invented for performing Fourier transforms [1] (including nature’s own such asthe human ear). Most of them are now of merely historical interest since the arrival ofthe computer–based algorithm known as the fast Fourier transform(FFT) [2, 3] whichefficiently computes the discrete Fourier transform. The FFT algorithm can also bephrased in terms of quantum dynamics, i.e., in terms of unitary operations performedby a quantumcomputeron quantumregisters. Indeed, all known quantumalgorithmsemploy the quantum version of Fourier transforms, either explicitly or indirectly. Itis used for the periodicity estimation in the Shor algorithm [4] and its approximateversion (the Hadamard transform) is commonly used to prepare quantum registersin coherent superpositions of different values.In this paper we analyse the performance of the quantum Fourier transform(QFT) in the presence of decoherence. In particular we show that as far as the peri-1

Carbon nanotubes as electrodes for dielectrophoresis of DNA

Dielectrophoresis can potentially be used as an efficient trapping tool in the fabrication of molecular devices. For nanoscale objects, however, the Brownian motion poses a challenge. We show that the use of carbon nanotube electrodes makes it possible to apply relatively low trapping voltages and still achieve high enough field gradients for trapping nanoscale objects, e.g., single molecules. We compare the efficiency and other characteristics of dielectrophoresis between carbon nanotube electrodes and lithographically fabricated metallic electrodes, in the case of trapping nanoscale DNA molecules. The results are analyzed using finite element method simulations and reveal information about the frequency-dependent polarizability of DNA.