Stimulated plasmon polariton scattering

The plasmon and phonon polaritons of two-dimensional (2d) and van-der-Waals materials have recently gained substantial interest. Unfortunately, they are notoriously hard to observe in linear response because of their strong confinement, low frequency and longitudinal mode symmetry. Here, we propose a fundamentally new approach of harnessing nonlinear resonant scattering that we call stimulated plasmon polariton scattering (SPPS) in analogy to the opto-acoustic stimulated Brillouin scattering (SBS). We show that SPS allows to excite, amplify and detect 2d plasmon and phonon polaritons all across the THz-range while requiring only optical components in the near-IR or visible range. We present a coupled-mode theory framework for SPS and based on this find that SPS power gains exceed the very top gains observed in on-chip SBS by at least an order of magnitude. This opens exciting new possibilities to fundamental studies of 2d materials and will help closing the THz gap in spectrocopy and information technology.Comment: 7 pages, 3 figure

Enhanced ponderomotive force in graphene due to interband resonance

We analyze intrinsic nonlinearities in two-dimensional polaritonic materials interacting with an optical wave. Focusing on the case of graphene, we show that the second-order nonlinear optical conductivity due to carrier density fluctuations associated with the excitation of a plasmon polariton is closely related to the ponderomotive force due to the oscillating optical field. This relation is first established through an elegant thermodynamic approach for a Drude-like plasma, in the frequency range where intraband scattering is the dominant contribution to conductivity. Subsequently, we extend our analysis to the interband regime, and show that for energies approximately half the Fermi energy, the intraband contribution to the ponderomotive force diverges. In practice, thermal broadening regularizes this divergence as one would expect, but even at room temperature typically leaves a strong ponderomotive enhancement. Finally, we study the impact of nonlocal corrections and find that nonlocality does not lead to further broadening (as one would expect in the case of Landau damping), but rather to a splitting of the ponderomotive interband resonance. Our analysis should prove useful to the open quest for exploiting nonlinearities in graphene and other two-dimensional polaritonic materials, through effects such as second harmonic generation and photon drag.Comment: 7 pages, 2 figures, 1 appendi

Quantum computing via defect states in two-dimensional anti-dot lattices

We propose a new structure suitable for quantum computing in a solid state environment: designed defect states in antidot lattices superimposed on a two-dimensional electron gas at a semiconductor heterostructure. State manipulation can be obtained with gate control. Model calculations indicate that it is feasible to fabricate structures whose energy level structure is robust against thermal dephasing.Comment: 4 pages including 3 figure

John F. Kennedy -Leadership Qualities That Moved A Nation

Leadership studies ask 'what makes an effective leader?' To answer this question analyses have to become practical and real-world oriented. The research question in this thesis is: 'How can the three factors - vision, decision-making style, and delegation - explain whether John F. Kennedy was an effective President?'While there are many other leadership factors such as integrity, political/legislative skills and communications skills three factors were chosen. 'Vision' mobilizes external support for the leader's overarching goals, and charts out a national direction. 'Decision making style' focuses on the 'internal', process-oriented aspects of leadership. The Delegation factor assesses what competence and perspectives that will bring input into the decision-making which will carry out the vision.The research methodology has been to conduct a single case study. His two year and ten months Presidency was short but contained several important Cold War eventsivThe Vision HypothesisA President will be effective if he has a compelling vision of the future of AmericaThe MA thesis tested whether 'The New Frontier' was a successful vision from which visionary initiatives were derived. The Moon Project was the most ambitious national scientific project in two decades, propelling the U.S. for-ward in the space race.JFK's ideas on peaceful cooperation with the Soviets were a consequence of the Cuban Missile Crisis. The vision was enunciated with his 'Strategy of Peace' speech at American University, in which he pledged for a pause in the Cold War, and announced the signing of the Test Ban Treaty.In the selected cases he strived to educate the American public on urgent needs by pursuing longer-term goals in the interest of national security.The Decision Making Style HypothesisA President will be effective if he has a competent personal decision making styleThe thesis tested whether President JFK had an effective personal decision making style. JFK often took issues out of the bureaucratic system in time to defend his own right to decide and his own right of innovation. JFK's collegial decision making model was a consensus-seeking vehicle which ensured that problems were debated through cross-fertilization.vThe Delegation Hypothesis:A President will be effective if he delegates with an eye to his political controlJFK knew what he was looking for in every position. Secretary of State Dean Rusk was probably chosen because JFK had conceived a greater role for himself in this area. Recent scholarly work has demonstrated that JFK was one of the most engaged Presidents in foreign affairs. Secretary of Defense Robert S. McNamara was chosen as a rational, intelligent civilian that could provide political control over the military establishment.Speech Writer Ted Sorensen knew JFK's intellectual ideas, and they cooperated closely on the speeches of the Administration. JFK relied on external advisors to balance decision-making information, and the British Ambassador Ormsby-Gore saw his ideas being put into use with regards to the quarantine line in the Cuban Missile Crisis.JFK's selection of advisors reflected the strengths and weaknesses of his own policy experience, demonstrating what Neustadt calls a 'rare' fine distinction among his 'fellow kings'.The thesis concludes by briefly testing the three factors in a comparison between President JFK and President George W. Bush, and finds that the current administration seems to have set too ambitious goals in its vision lacking good contextual intelligence

Failure of standard approximations of the exchange coupling in nanostructures

We calculate the exchange coupling for a double dot system using a novel, numerically exact yet efficient technique, based on finite-element methods. Specifically, we evaluate the exchange coupling both for a quasi-one and a two-dimensional system, also including an applied magnetic field. Our numerical results provide a stringent test for standard approximation schemes (e.g., Heitler-London, Hund-Mulliken, Hubbard), and they show that the standard methods do not have reliable predictive power for real quantum-dot systems.Comment: 7 pages, 4 figure

Experimental investigation of cut-off phenomena in non-linear photonic crystal fibers

The modal cut-off is investigated experimentally in a series of high quality non-linear photonic crystal fibers. We demonstrate a suitable measurement technique to determine the cut-off wavelength and verify it by inspecting the near field of the modes that may be excited below and above the cut-off. We observe a double peak structure in the cut-off spectra, which is attributed to a splitting of the higher order modes. The cut-off is measured for seven different fiber geometries with different pitches and relative hole size, and a very good agreement with recent theoretical work is found.Comment: 3 pages including 1 table and 4 figures. Accepted for Optics Letter

Embodied Tuning: Interfacing Danish Radio Heritage

Most museum exhibitions favor vision, not hearing. When there is audio in exhibitions, it tends to take on a secondary role as a soundtrack or commentary. In some cases, however, audio should be the primary object of interest. Radio heritage is such a case. The traditional way of showcasing audio is through webaccessible archives or through listening kiosks in the exhibition. Neither one takes advantage of the unique affordances of the spatiality and physicality of an exhibition. We therefore propose an alternative way of exhibiting radio heritage in a listening exhibition where users move around and explore the physical gallery space. We implemented a simple, low-cost prototype system called Exaudimus, allowing users to search for the audio streams using their own bodies as a metaphorical radio-tuning dial. We tested the concept in a public exhibition at the Media Museum in Denmark. A small, qualitative user study conducted during the exhibition shows promise for this type of immersive experience. The users, however, tended to perceive it as