Localized exciton-polariton modes in dye-doped nanospheres: a quantum approach

We model a dye-doped polymeric nanosphere as an ensemble of quantum emitters and use it to investigate the localized exciton-polaritons supported by such a nanosphere. By determining the time evolution of the density matrix of the collective system, we explore how an incident laser field may cause transient optical field enhancement close to the surface of such nanoparticles. Our results provide further evidence that excitonic materials can be used to good effect in nanophotonics.Comment: 16 pages, 4 figure

Quantum Brownian Motion for Magnets

Spin precession in magnetic materials is commonly modelled with the classical phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized spin+environment Hamiltonian, we here derive a general spin operator equation of motion that describes three-dimensional precession and damping and consistently accounts for effects arising from memory, coloured noise and quantum statistics. The LLG equation is recovered as its classical, Ohmic approximation. We further introduce resonant Lorentzian system--reservoir couplings that allow a systematic comparison of dynamics between Ohmic and non--Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a spin in the semi--classical limit. At low temperatures, our numerical results demonstrate a characteristic reduction and flattening of the steady state spin alignment with an external field, caused by the quantum statistics of the environment. The results provide a powerful framework to explore general three-dimensional dissipation in quantum thermodynamics.Comment: substantially updated version, 5 figures, 12 pages+refs+appendix, comments welcome (previous title: Versatile three-dimensional quantum spin dynamics equation with guaranteed fluctuation-dissipation link

The electric dipole moment of the nucleon from simulations at imaginary vacuum angle theta

We compute the electric dipole moment of proton and neutron from lattice QCD simulations with N_f=2 flavors of dynamical quarks at imaginary vacuum angle theta. The calculation proceeds via the CP odd form factor F_3. A novel feature of our calculation is that we use partially twisted boundary conditions to extract F_3 at zero momentum transfer. As a byproduct, we test the QCD vacuum at nonvanishing theta.Comment: 22 pages, 10 figure

Theory of Linear Spin Wave Emission from a Bloch Domain Wall

We report an analytical theory of linear emission of exchange spin waves from a Bloch domain wall, excited by a uniform microwave magnetic field. The problem is reduced to a one-dimensional Schr\"odinger-like equation with a P\"oschl-Teller potential and a driving term of the same profile. The emission of plane spin waves is observed at excitation frequencies above a threshold value, as a result of a linear process. The height-to-width aspect ratio of the P\"oschl-Teller profile for a domain wall is found to correspond to a local maximum of the emission efficiency. Furthermore, for a tailored P\"oschl-Teller potential with a variable aspect ratio, particular values of the latter can lead to enhanced or even completely suppressed emission.Comment: added ancillary file

Improving the lattice axial vector current

For Wilson and clover fermions traditional formulations of the axial vector current do not respect the continuum Ward identity which relates the divergence of that current to the pseudoscalar density. Here we propose to use a point-split or one-link axial vector current whose divergence exactly satisfies a lattice Ward identity, involving the pseudoscalar density and a number of irrelevant operators. We check in one-loop lattice perturbation theory with SLiNC fermion and gauge plaquette action that this is indeed the case including order $O(a)$ effects. Including these operators the axial Ward identity remains renormalisation invariant. First preliminary results of a nonperturbative check of the Ward identity are also presented.Comment: 7 pages, 3 figures, Proceedings of the 33rd International Symposium on Lattice Field Theory, 14-18 July 2015, Kobe, Japa

Prospecting for new questions: integrating geophysics to define anthropological research objectives and inform excavation strategies at monumental sites

Geophysical data have the potential to significantly contribute to archaeological research projects when effectively integrated with more traditional methods. Although pre-existing archaeological questions about a site may be answered using geophysical methods, beginning an investigation with an extensive geophysical survey can assist in understanding the function and archaeological potential of a site, and may even transform preconceptions about the type and spatial organisation of features that are present. In this way, these prospection tools not only accurately locate and map features to allow recovery of cultural material for identification and dating, we argue that they can go much further, allowing us to prospect for new and appropriate archaeological and anthropological research questions. Such an approach is best realised when geophysical and traditional archaeologists work together to define new objectives and strategies to address them, and by maintaining this collaboration to allow continual feedback between geophysical and archaeological data. A flexible research design is therefore essential in order to allow the methodologies to adapt to the site, the results, and the questions being posed. This methodology is demonstrated through two case studies from mound sites in southeast USA: the transitional Mississippian Washausen site in Illinois; and the Middle Woodland Garden Creek site in North Carolina. In both cases, integrating geophysical methods throughout the archaeological investigations has resulted in multiple phases of generating and addressing new research objectives. Although clearly beneficial at these two mound sites in southeast USA, this interdisciplinary approach has obvious implications well beyond these temporal and geographical areas

Prospecting for new questions: integrating geophysics to define anthropological research objectives and inform excavation strategies at monumental sites

Geophysical data have the potential to significantly contribute to archaeological research projects when effectively integrated with more traditional methods. Although pre-existing archaeological questions about a site may be answered using geophysical methods, beginning an investigation with an extensive geophysical survey can assist in understanding the function and archaeological potential of a site, and may even transform preconceptions about the type and spatial organisation of features that are present. In this way, these prospection tools not only accurately locate and map features to allow recovery of cultural material for identification and dating, we argue that they can go much further, allowing us to prospect for new and appropriate archaeological and anthropological research questions. Such an approach is best realised when geophysical and traditional archaeologists work together to define new objectives and strategies to address them, and by maintaining this collaboration to allow continual feedback between geophysical and archaeological data. A flexible research design is therefore essential in order to allow the methodologies to adapt to the site, the results, and the questions being posed. This methodology is demonstrated through two case studies from mound sites in southeast USA: the transitional Mississippian Washausen site in Illinois; and the Middle Woodland Garden Creek site in North Carolina. In both cases, integrating geophysical methods throughout the archaeological investigations has resulted in multiple phases of generating and addressing new research objectives. Although clearly beneficial at these two mound sites in southeast USA, this interdisciplinary approach has obvious implications well beyond these temporal and geographical areas

Renormalization of local quark-bilinear operators for Nf=3 flavors of SLiNC fermions

The renormalization factors of local quark-bilinear operators are computed non-perturbatively for $N_f=3$ flavors of SLiNC fermions, with emphasis on the various procedures for the chiral and continuum extrapolations. The simulations are performed at a lattice spacing $a=0.074$ fm, and for five values of the pion mass in the range of 290-465 MeV, allowing a safe and stable chiral extrapolation. Emphasis is given in the subtraction of the well-known pion pole which affects the renormalization factor of the pseudoscalar current. We also compute the inverse propagator and the Green's functions of the local bilinears to one loop in perturbation theory. We investigate lattice artifacts by computing them perturbatively to second order as well as to all orders in the lattice spacing. The renormalization conditions are defined in the RI$'$-MOM scheme, for both the perturbative and non-perturbative results. The renormalization factors, obtained at different values of the renormalization scale, are translated to the ${\bar{\rm MS}}$ scheme and are evolved perturbatively to 2 GeV. Any residual dependence on the initial renormalization scale is eliminated by an extrapolation to the continuum limit. We also study the various sources of systematic errors. Particular care is taken in correcting the non-perturbative estimates by subtracting lattice artifacts computed to one loop perturbation theory using the same action. We test two different methods, by subtracting either the ${\cal O}(g^2\,a^2)$ contributions, or the complete (all orders in $a$) one-loop lattice artifacts.Comment: 33 pages, 27 figures, 6 table