5,411 research outputs found
Mesoscopic Mechanical Resonators as Quantum Non-Inertial Reference Frames
An atom attached to a micrometer-scale wire that is vibrating at a frequency
of 100 MHz and with displacement amplitude 1 nm experiences an acceleration
magnitude 10^9 ms^-2, approaching the surface gravity of a neutron star. As one
application of such extreme non-inertial forces in a mesoscopic setting, we
consider a model two-path atom interferometer with one path consisting of the
100 MHz vibrating wire atom guide. The vibrating wire guide serves as a
non-inertial reference frame and induces an in principle measurable phase shift
in the wave function of an atom traversing the wire frame. We furthermore
consider the effect on the two-path atom wave interference when the vibrating
wire is modeled as a quantum object, hence functioning as a quantum
non-inertial reference frame. We outline a possible realization of the
vibrating wire, atom interferometer using a superfluid helium quantum
interference setup.Comment: Published versio
Measurement of energy eigenstates by a slow detector
We propose a method for a weak continuous measurement of the energy
eigenstates of a fast quantum system by means of a "slow" detector. Such a
detector is only sensitive to slowly-changing variables, e. g. energy, while
its back-action can be limited solely to decoherence of the eigenstate
superpositions. We apply this scheme to the problem of detection of quantum
jumps between energy eigenstates in a harmonic oscillator.Comment: 4 page
Quantum measurement backaction from a BEC coupled to a mechanical oscillator
We study theoretically the dynamics of a a hybrid optomechanical system
consisting of a macroscopic mechanical membrane magnetically coupled to a
spinor Bose-Einstein condensate via a nanomagnet attached at the membrane
center. We demonstrate that this coupling permits us to monitor indirectly the
center-of-mass position of the membrane via measurements of the spin of the
condensed atoms. These measurements normally induce a significant backaction on
the membrane motion, which we quantify for the cases of thermal and coherent
initial states of the membrane. We discuss the possibility of measuring that
quantum backaction via repeated measurements. We also investigate the potential
to generate non-classical states of the membrane, in particular Schrodinger cat
states, via such repeated measurements.Comment: 14 pages, 4 figures. Submitted to PR
Schwann cells migrate along axons in the absence of GDNF signaling
BACKGROUND: During development neural crest derived Schwann Cell (SC) precursors migrate to nerve trunks and populate nascent nerves. Axonal ensheathment by SC is a prerequisite for normal nerve function and the integrity of myelinated as well as nonmyelinated axons. To provide adequate support functions, SC colonize entire nerves. One important prerequisite for this is their migration into distal axonal regions. RESULTS: Here, we studied the role of Glial cell line derived neurotrophic factor (GDNF), a TGF-beta related growth factor, for SC migration. To this end we used a superior cervical ganglion (SCG) explant-SC migration assay, GDNF null mutant mouse embryos and a chemical inhibitor for GDNF signaling in combination with time-lapse imaging. We found that GDNF signaling is dispensable for SC migration along murine embryonic sympathetic axons. Furthermore, in vivo analyzes revealed that SC migration along the sciatic nerve is also not dependent on GDNF. CONCLUSIONS: In contrast to previous in vitro findings in the sciatic nerve and a SC precursor cell line, our results clearly indicate that GDNF is dispensable for embryonic SC migration. This is demonstrated for the sympathetic nervous system and also for the sciatic nerve in mouse
Cooling a mechanical resonator via coupling to a tunable double quantum dot
We study the cooling of a mechanical resonator (MR) that is capacitively
coupled to a double quantum dot (DQD). The MR is cooled by the dynamical
backaction induced by the capacitive coupling between the DQD and the MR. The
DQD is excited by a microwave field and afterwards a tunneling event results in
the decay of the excited state of the DQD. An important advantage of this
system is that both the energy level splitting and the decay rate of the DQD
can be well tuned by varying the gate voltage. We find that the steady average
occupancy, below unity, of the MR can be achieved by changing both the decay
rate of the excited state and the detuning between the transition frequency of
the DQD and the microwave frequency, in analogy to the laser sideband cooling
of an atom or trapped ion in atomic physics. Our results show that the cooling
of the MR to the ground state is experimentally implementable.Comment: 10 pages, 5 figure
Dissipation in nanocrystalline-diamond nanomechanical resonators
We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^(0.2), with Q^(–1) ≈ 10^(–4) at low temperatures. The frequency dependence of a large dissipation feature at ~35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz
Enhancement of Cavity Cooling of a Micromechanical Mirror Using Parametric Interactions
It is shown that an optical parametric amplifier inside a cavity can
considerably improve the cooling of the micromechanical mirror by radiation
pressure. The micromechanical mirror can be cooled from room temperature 300 K
to sub-Kelvin temperatures, which is much lower than what is achievable in the
absence of the parametric amplifier. Further if in case of a precooled mirror
one can reach millikelvin temperatures starting with about 1 K. Our work
demonstrates the fundamental dependence of radiation pressure effects on photon
statistics.Comment: 14 pages, 7 figure
Self-cooling of a micro-mirror by radiation pressure
We demonstrate passive feedback cooling of a mechanical resonator based on
radiation pressure forces and assisted by photothermal forces in a high-finesse
optical cavity. The resonator is a free-standing high-reflectance micro-mirror
(of mass m=400ng and mechanical quality factor Q=10^4) that is used as
back-mirror in a detuned Fabry-Perot cavity of optical finesse F=500. We
observe an increased damping in the dynamics of the mechanical oscillator by a
factor of 30 and a corresponding cooling of the oscillator modes below 10 K
starting from room temperature. This effect is an important ingredient for
recently proposed schemes to prepare quantum entanglement of macroscopic
mechanical oscillators.Comment: 11 pages, 9 figures, minor correction
alpha-Amylase Production in Fed BatchCultivation of Bacillus caldolyticus: An Interpretation of FermentationCourseUsing 2-D Gel Electrophoresis
The conditions for increased production of thermostable a-amylase from Bacillus caldolyticus DSM 405 were investigated. Preliminary experiments in batch shake flasks led to an optimized initial cultivation medium. Shake flask experiments in extended-batch
and in fed-batch mode of operation indicated that the a-amylase production was enhanced by continuous feeding of starch. The activity of the a-amylase with optimized initial medium in batch-operated shake flasks was 5.7 U mL–1 compared to 15.4U mL–1 in the extended-batch culture and 21 U mL–1 in fed-batch culture. The improvements were achieved by avoiding any excess of starch in medium that led to accumulation of glucose followed by acetate formation. Adding casitone as the second component of the
feeding solution in an aerated and agitated fed-batch bioreactor (3-liter working volume) led to an increased -amylase activity of up to 163.7 U mL.–1 All phases of cultivation were analyzed using 2D-gel electrophoresis in combination with nano LC-ESI-MS/MS for identification of altered proteins. Pyruvate kinase, 6-phosphofructokinase, GltC, anti-sigma F factor, glycogen synthase and several important variable proteins were detected. With help of these results, potential improvements of a two-component feeding strategy are discussed
- …