Electrically-tunable hole g-factor of an optically-active quantum dot for fast spin rotations

We report a large g-factor tunability of a single hole spin in an InGaAs quantum dot via an electric field. The magnetic field lies in the in-plane direction x, the direction required for a coherent hole spin. The electrical field lies along the growth direction z and is changed over a large range, 100 kV/cm. Both electron and hole g-factors are determined by high resolution laser spectroscopy with resonance fluorescence detection. This, along with the low electrical-noise environment, gives very high quality experimental results. The hole g-factor g_xh depends linearly on the electric field Fz, dg_xh/dFz = (8.3 +/- 1.2)* 10^-4 cm/kV, whereas the electron g-factor g_xe is independent of electric field, dg_xe/dFz = (0.1 +/- 0.3)* 10^-4 cm/kV (results averaged over a number of quantum dots). The dependence of g_xh on Fz is well reproduced by a 4x4 k.p model demonstrating that the electric field sensitivity arises from a combination of soft hole confining potential, an In concentration gradient and a strong dependence of material parameters on In concentration. The electric field sensitivity of the hole spin can be exploited for electrically-driven hole spin rotations via the g-tensor modulation technique and based on these results, a hole spin coupling as large as ~ 1 GHz is expected to be envisaged.Comment: 8 pages, 4 figure

Where the Grass is Greener — Large-Scale Phenological Patterns and Their Explanatory Potential for the Distribution of Paleolithic Hunter-Gatherers in Europe

A unique property of the Paleolithic record is the possibility to observe human societies in large areas and over long periods of time. At these large spatial and temporal scales, a number of interesting phenomena can be observed, such as dynamics in the distribution of populations in relation to equally large-scale environmental patterns. In this paper, we focus on phenological patterns of vegetation and discuss their explanatory potential for differences in site densities in different periods and parts of Europe. In particular, we present a case-transferable approach to diachronically estimate the timing of the vegetation period and resulting phenological gradients. We discuss results for two complementary case studies. First, we look at the Aurignacian in Western and Central Europe, a period of dynamic population dispersal in a topographically heterogeneous region. Second, we focus on the Middle and Late Upper Paleolithic in the East European Plain, a period after the arrival of anatomically modern humans in a topographically rather uniform area. We visualize phenological trajectories and boundaries otherwise invisible in the archaeological record with certain explanatory potential for the observed archaeological patterns. Importantly, we do not intend to reconstruct specific plant communities or dispersal routes of animals or humans. Rather, we aim at highlighting gradients which in themselves and on small temporal scales might be comparatively weak, but over the course of millennia may potentially influence the distribution of animal biomass and human populations by biasing the aggregate of at times opposing actions of individuals towards particular directions

Observable and hidden singular features of large fluctuations in nonequilibrium systems

We study local features, and provide a topological insight into the global structure of the probability density distribution and of the pattern of the optimal paths for large rare fluctuations away from a stable state. In contrast to extremal paths in quantum mechanics, the optimal paths do {\it not} encounter caustics. We show how this occurs, and what, instead of caustics, are the experimentally observable singularities of the pattern. We reveal the possibility for a caustic and a switching line to start at a saddle point, and discuss the consequences.Comment: 10 pages, 3 ps figures by request, LaTeX Article Format (In press, Phys. Lett. A

The Effect of Focusing and Caustics on Exit Phenomena in Systems Lacking Detailed Balance

We study the trajectories followed by a particle subjected to weak noise when escaping from the domain of attraction of a stable fixed point. If detailed balance is absent, a _focus_ may occur along the most probable exit path, leading to a breakdown of symmetry (if present). The exit trajectory bifurcates, and the exit location distribution may become `skewed' (non-Gaussian). The weak-noise asymptotics of the mean escape time are strongly affected. Our methods extend to the study of skewed exit location distributions in stochastic models without symmetry.Comment: REVTEX macros (latest version). Two accompanying PS figures, one of which is large (over 600K unpacked

Preserving cultural heritage: Analyzing the antifungal potential of ionic liquids tested in paper restoration

Early industrialization and the development of cheap production processes for paper have led to an exponential accumulation of paper-based documents during the last two centuries. Archives and libraries harbor vast amounts of ancient and modern documents and have to undertake extensive endeavors to protect them from abiotic and biotic deterioration. While services for mechanical preservation such as ex post de-acidification of historic documents are already commercially available, the possibilities for long-term protection of paper-based documents against fungal attack (apart from temperature and humidity control) are very limited. Novel processes for mechanical enhancement of damaged cellulosic documents use Ionic Liquids (IL) as essential process components. With some of these ILs having azolefunctionalities similar to well-known fungicides such as Clotrimazole, the possibility of antifungal activities of these ILs was proposed but has not yet been experimentally confirmed. We evaluated the potency of four ILs with potential application in paper restoration for suppression of fungal growth on five relevant paper-infesting molds. The results revealed a general antifungal activity of all ILs, which increased with the size of the non-polar group. Physiological experiments and ultimate elemental analysis allowed to determine the minimal inhibitory concentration of each IL as well as the residual IL concentration in process-treated paper. These results provide valuable guidelines for IL-applications in paper restoration processes with antifungal activity as an added benefit. With azoles remaining in the paper after the process, simultaneous repair and biotic protection in treated documents could be facilitated

The Escape Problem for Irreversible Systems

The problem of noise-induced escape from a metastable state arises in physics, chemistry, biology, systems engineering, and other areas. The problem is well understood when the underlying dynamics of the system obey detailed balance. When this assumption fails many of the results of classical transition-rate theory no longer apply, and no general method exists for computing the weak-noise asymptotics of fundamental quantities such as the mean escape time. In this paper we present a general technique for analysing the weak-noise limit of a wide range of stochastically perturbed continuous-time nonlinear dynamical systems. We simplify the original problem, which involves solving a partial differential equation, into one in which only ordinary differential equations need be solved. This allows us to resolve some old issues for the case when detailed balance holds. When it does not hold, we show how the formula for the mean escape time asymptotics depends on the dynamics of the system along the most probable escape path. We also present new results on short-time behavior and discuss the possibility of focusing along the escape path.Comment: 24 pages, APS revtex macros (version 2.1) now available from PBB via `get oldrevtex.sty

A Scaling Theory of Bifurcations in the Symmetric Weak-Noise Escape Problem

We consider the overdamped limit of two-dimensional double well systems perturbed by weak noise. In the weak noise limit the most probable fluctuational path leading from either point attractor to the separatrix (the most probable escape path, or MPEP) must terminate on the saddle between the two wells. However, as the parameters of a symmetric double well system are varied, a unique MPEP may bifurcate into two equally likely MPEP's. At the bifurcation point in parameter space, the activation kinetics of the system become non-Arrhenius. In this paper we quantify the non-Arrhenius behavior of a system at the bifurcation point, by using the Maslov-WKB method to construct an approximation to the quasistationary probability distribution of the system that is valid in a boundary layer near the separatrix. The approximation is a formal asymptotic solution of the Smoluchowski equation. Our analysis relies on the development of a new scaling theory, which yields `critical exponents' describing weak-noise behavior near the saddle, at the bifurcation point.Comment: LaTeX, 60 pages, 24 Postscript figures. Uses epsf macros to include the figures. A file in `uufiles' format containing the figures is separately available at ftp://platinum.math.arizona.edu/pub/papers-rsm/paperF/figures.uu and a Postscript version of the whole paper (figures included) is available at ftp://platinum.math.arizona.edu/pub/papers-rsm/paperF/paperF.p