Generation of mechanical squeezing via magnetic dipoles on cantilevers

A scheme to squeeze the center-of-mass motional quadratures of a quantum mechanical oscillator below its standard quantum limit is proposed and analyzed theoretically. It relies on the dipole-dipole coupling between a magnetic dipole mounted on the tip of a cantilever to equally oriented dipoles located on a mesoscopic tuning fork. We also investigate the influence of several sources of noise on the achievable squeezing, including classical noise in the driving fork and the clamping noise in the oscillator. A detection of the state of the cantilever based on state transfer to a light field is considered. We investigate possible limitations of that scheme.Comment: 11 pages, 11 figures, submitted to PR

Impurity and Trace Tritium Transport in Tokamak Edge Turbulence

The turbulent transport of impurity or minority species, as for example Tritium, is investigated in drift-Alfv\'en edge turbulence. The full effects of perpendicular and parallel convection are kept for the impurity species. The impurity density develops a granular structure with steep gradients and locally exceeds its initial values due to the compressibility of the flow. An approximate decomposition of the impurity flux into a diffusive part and an effective convective part (characterized by a pinch velocity) is performed and a net inward pinch effect is recovered. The pinch velocity is explained in terms of Turbulent Equipartition and is found to vary poloidally. The results show that impurity transport modeling needs to be two-dimensional, considering besides the radial direction also the strong poloidal variation in the transport coefficients.Comment: 12 Pages, 5 Figure

Cavity cooling of an optically trapped nanoparticle

We study the cooling of a dielectric nanoscale particle trapped in an optical cavity. We derive the frictional force for motion in the cavity field, and show that the cooling rate is proportional to the square of oscillation amplitude and frequency. Both the radial and axial centre-of-mass motion of the trapped particle, which are coupled by the cavity field, are cooled. This motion is analogous to two coupled but damped pendulums. Our simulations show that the nanosphere can be cooled to 1/e of its initial momentum over time scales of hundredths of milliseconds.Comment: 11 page

Demonstration of an erbium doped microdisk laser on a silicon chip

An erbium doped micro-laser is demonstrated utilizing $\mathrm{SiO_{2}}$ microdisk resonators on a silicon chip. Passive microdisk resonators exhibit whispering gallery type (WGM) modes with intrinsic optical quality factors of up to $6\times{10^{7}}$ and were doped with trivalent erbium ions (peak concentration $\mathrm{\sim3.8\times{10^{20}cm^{-3})}}$ using MeV ion implantation. Coupling to the fundamental WGM of the microdisk resonator was achieved by using a tapered optical fiber. Upon pumping of the $^{4}I_{15/2}\longrightarrow$ $^{4}I_{13/2}$ erbium transition at 1450 nm, a gradual transition from spontaneous to stimulated emission was observed in the 1550 nm band. Analysis of the pump-output power relation yielded a pump threshold of 43 $\mathrm{\mu}$W and allowed measuring the spontaneous emission coupling factor: $\beta\approx1\times10^{-3}$

Cavity spin optodynamics

The dynamics of a large quantum spin coupled parametrically to an optical resonator is treated in analogy with the motion of a cantilever in cavity optomechanics. New spin optodynamic phenonmena are predicted, such as cavity-spin bistability, optodynamic spin-precession frequency shifts, coherent amplification and damping of spin, and the spin optodynamic squeezing of light.Comment: 4 pages, 3 figure

Collisional transport across the magnetic field in drift-fluid models

Drift ordered fluid models are widely applied in studies of low-frequency turbulence in the edge and scrape-off layer regions of magnetically confined plasmas. Here, we show how collisional transport across the magnetic field is self-consistently incorporated into drift-fluid models without altering the drift-fluid energy integral. We demonstrate that the inclusion of collisional transport in drift-fluid models gives rise to diffusion of particle density, momentum and pressures in drift-fluid turbulence models and thereby obviate the customary use of artificial diffusion in turbulence simulations. We further derive a computationally efficient, two-dimensional model which can be time integrated for several turbulence de-correlation times using only limited computational resources. The model describes interchange turbulence in a two-dimensional plane perpendicular to the magnetic field located at the outboard midplane of a tokamak. The model domain has two regions modeling open and closed field lines. The model employs a computational expedient model for collisional transport. Numerical simulations show good agreement between the full and the simplified model for collisional transport

The Hall instability of weakly ionized, radially stratified, rotating disks

Cool weakly ionized gaseous rotating disk, are considered by many models as the origin of the evolution of protoplanetary clouds. Instabilities against perturbations in such disks play an important role in the theory of the formation of stars and planets. Thus, a hierarchy of successive fragmentations into smaller and smaller pieces as a part of the Kant-Laplace theory of formation of the planetary system remains valid also for contemporary cosmogony. Traditionally, axisymmetric magnetohydrodynamic (MHD), and recently Hall-MHD instabilities have been thoroughly studied as providers of an efficient mechanism for radial transfer of angular momentum, and of density radial stratification. In the current work, the Hall instability against nonaxisymmetric perturbations in compressible rotating fluids in external magnetic field is proposed as a viable mechanism for the azimuthal fragmentation of the protoplanetary disk and thus perhaps initiating the road to planet formation. The Hall instability is excited due to the combined effect of the radial stratification of the disk and the Hall electric field, and its growth rate is of the order of the rotation period.Comment: 15 pages, 2 figure

Dissipation in intercluster plasma

We discuss dissipative processes in strongly gyrotropic, nearly collisionless plasma in clusters of galaxies (ICM). First, we point out that Braginsky theory, which assumes that collisions are more frequent that the system's dynamical time scale, is inapplicable to fast, sub-viscous ICM motion. Most importantly, the electron contribution to collisional magneto-viscosity dominates over that of ions for short-scale Alfvenic motions. Thus, if a turbulent cascade develops in the ICM and propagates down to scales $\leq 1$ kpc, it is damped collisionally not on ions, but on electrons. Second, in high beta plasma of ICM, small variations of the magnetic field strength, of relative value $\sim 1/\beta$, lead to development of anisotropic pressure instabilities (firehose, mirror and cyclotron). Unstable wave modes may provide additional resonant scattering of particles, effectively keeping the plasma in a state of marginal stability. We show that in this case the dissipation rate of a laminar, subsonic, incompressible flows scales as inverse of plasma beta parameter. We discuss application to the problem of ICM heating.Comment: 4 pages, accepted by ApJ Let

Turbulence, magnetic fields and plasma physics in clusters of galaxies

Observations of galaxy clusters show that the intracluster medium (ICM) is likely to be turbulent and is certainly magnetized. The properties of this magnetized turbulence are determined both by fundamental nonlinear magnetohydrodynamic interactions and by the plasma physics of the ICM, which has very low collisionality. Cluster plasma threaded by weak magnetic fields is subject to firehose and mirror instabilities. These saturate and produce fluctuations at the ion gyroscale, which can scatter particles, increasing the effective collision rate and, therefore, the effective Reynolds number of the ICM. A simple way to model this effect is proposed. The model yields a self-accelerating fluctuation dynamo whereby the field grows explosively fast, reaching the observed, dynamically important, field strength in a fraction of the cluster lifetime independent of the exact strength of the seed field. It is suggested that the saturated state of the cluster turbulence is a combination of the conventional isotropic magnetohydrodynamic turbulence, characterized by folded, direction-reversing magnetic fields and an Alfv\'en-wave cascade at collisionless scales. An argument is proposed to constrain the reversal scale of the folded field. The picture that emerges appears to be in qualitative agreement with observations of magnetic fields in clusters.Comment: revtex, 9 pages, 5 figures; invited talk for the 47th APS DPP Meeting, Denver, CO, Oct 2005; minor corrections to match the published versio