316 research outputs found
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
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
microdisk resonators on a silicon chip. Passive microdisk resonators exhibit
whispering gallery type (WGM) modes with intrinsic optical quality factors of
up to and were doped with trivalent erbium ions (peak
concentration 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 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
W and allowed measuring the spontaneous emission coupling factor:
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
High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators
The inherent coupling of optical and mechanical modes in high finesse optical
microresonators provide a natural, highly sensitive transduction mechanism for
micromechanical vibrations. Using homodyne and polarization spectroscopy
techniques, we achieve shot-noise limited displacement sensitivities of
10^(-19) m Hz^(-1/2). In an unprecedented manner, this enables the detection
and study of a variety of mechanical modes, which are identified as radial
breathing, flexural and torsional modes using 3-dimensional finite element
modelling. Furthermore, a broadband equivalent displacement noise is measured
and found to agree well with models for thermorefractive noise in silica
dielectric cavities. Implications for ground-state cooling, displacement
sensing and Kerr squeezing are discussed.Comment: 25 pages, 8 figure
Gravitational wave detection using electromagnetic modes in a resonance cavity
We present a proposal for a gravitational wave detector, based on the
excitation of an electromagnetic mode in a resonance cavity. The mode is
excited due to the interaction between a large amplitude electromagnetic mode
and a quasi-monochromatic gravitational wave. The minimum metric perturbation
needed for detection is estimated to the order 7.10^(-23) using current data on
superconducting niobium cavities. Using this value together with different
standard models predicting the occurrence of merging neutron star or black hole
binaries, the corresponding detection rate is estimated to 1-20 events per
year, with a `table top' cavity of a few meters length.Comment: 8 pages, 1 figure, references adde
Dust Dynamics in Compressible MHD Turbulence
We calculate the relative grain-grain motions arising from interstellar
magnetohydrodynamic (MHD) turbulence. The MHD turbulence includes both fluid
motions and magnetic fluctuations. While the fluid motions accelerate grains
through hydro-drag, the electromagnetic fluctuations accelerate grains through
resonant interactions. We consider both incompressive (Alfv\'{e}n) and
compressive (fast and slow) MHD modes and use descriptions of MHD turbulence
obtained in Cho & Lazarian (2002). Calculations of grain relative motion are
made for realistic grain charging and interstellar turbulence that is
consistent with the velocity dispersions observed in diffuse gas, including
cutoff of the turbulence from various damping processes. We show that fast
modes dominate grain acceleration, and can drive grains to supersonic
velocities. Grains are also scattered by gyroresonance interactions, but the
scattering is less important than acceleration for grains moving with
sub-Alfv\'{e}nic velocities. Since the grains are preferentially accelerated
with large pitch angles, the supersonic grains will be aligned with long axes
perpendicular to the magnetic field. We compare grain velocities arising from
MHD turbulence with those arising from photoelectric emission, radiation
pressure and H thrust. We show that for typical interstellar conditions
turbulence should prevent these mechanisms from segregating small and large
grains. Finally, gyroresonant acceleration is bound to preaccelerate grains
that are further accelerated in shocks. Grain-grain collisions in the shock may
then contribute to the overabundance of refractory elements in the composition
of galactic cosmic rays.Comment: 15 pages, 17 figure
Broad-band gravitational-wave pulses from binary neutron stars in eccentric orbits
Maximum gravitational wave emission from binary stars in eccentric orbits
occurs near the periastron passage. We show that for a stationary distribution
of binary neutron stars in the Galaxy, several high-eccentricity systems with
orbital periods in the range from tens of minutes to several days should exist
that emit broad gravitational-wave pulses in the frequency range 1-100 mHz. The
space interferometer LISA could register the pulsed signal from these system at
a signal-to-noise ratio level in the frequency range Hz during one-year observational time. Some detection
algorithms for such a signal are discussed.Comment: 17 pages, LATEX, 3 figures, Astronomy Letters, 2002, in press; typos
corrected, refference adde
Testing the neutrality of matter by acoustic means in a spherical resonator
New measurements to test the neutrality of matter by acoustic means are
reported. The apparatus is based on a spherical capacitor filled with gaseous
SF excited by an oscillating electric field. The apparatus has been
calibrated measuring the electric polarizability. Assuming charge conservation
in the decay of the neutron, the experiment gives a limit of
for the electron-proton charge
difference, the same limit holding for the charge of the neutron. Previous
measurements are critically reviewed and found incorrect: the present result is
the best limit obtained with this technique
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