930 research outputs found
Infant hospitalisations and fatalities averted by the maternal pertussis vaccination programme in England, 2012-2017: Post-implementation economic evaluation
In October 2012, a maternal pertussis vaccination programme was implemented in England following an increased incidence and mortality in infants. We evaluated the cost-effectiveness of the programme by comparing pertussis-related infant hospitalisations and deaths in 2012-2017 with non-vaccination scenarios. Despite considerable uncertainties, findings support the cost-effectiveness of the programme
Complete roughness and conductivity corrections for the recent Casimir force measurement
We consider detailed roughness and conductivity corrections to the Casimir
force in the recent Casimir force measurement employing an Atomic Force
Microscope. The roughness of the test bodies-a metal plate and a sphere- was
investigated with the Atomic Force Microscope and the Scanning Electron
Microscope respectively. It consists of separate crystals of different heights
and a stochastic background. The amplitude of roughness relative to the zero
roughness level was determined and the corrections to the Casimir force were
calculated up to the fourth order in a small parameter (which is this amplitude
divided by the distance between the two test bodies). Also the corrections due
to finite conductivity were found up to the fourth order in relative
penetration depth of electromagnetic zero point oscillations into the metal.
The theoretical result for the configuration of a sphere above a plate taking
into account both corrections is in excellent agreement with the measured
Casimir force
Quantum Dissipative Dynamics of the Magnetic Resonance Force Microscope in the Single-Spin Detection Limit
We study a model of a magnetic resonance force microscope (MRFM) based on the
cyclic adiabatic inversion technique as a high-resolution tool to detect single
electron spins. We investigate the quantum dynamics of spin and cantilever in
the presence of coupling to an environment. To obtain the reduced dynamics of
the combined system of spin and cantilever, we use the Feynman-Vernon influence
functional and get results valid at any temperature as well as at arbitrary
system-bath coupling strength. We propose that the MRFM can be used as a
quantum measurement device, i.e., not only to detect the modulus of the spin
but also its direction
An off-board quantum point contact as a sensitive detector of cantilever motion
Recent advances in the fabrication of microelectromechanical systems (MEMS)
and their evolution into nanoelectromechanical systems (NEMS) have allowed
researchers to measure extremely small forces, masses, and displacements. In
particular, researchers have developed position transducers with resolution
approaching the uncertainty limit set by quantum mechanics. The achievement of
such resolution has implications not only for the detection of quantum behavior
in mechanical systems, but also for a variety of other precision experiments
including the bounding of deviations from Newtonian gravity at short distances
and the measurement of single spins. Here we demonstrate the use of a quantum
point contact (QPC) as a sensitive displacement detector capable of sensing the
low-temperature thermal motion of a nearby micromechanical cantilever.
Advantages of this approach include versatility due to its off-board design,
compatibility with nanoscale oscillators, and, with further development, the
potential to achieve quantum limited displacement detection.Comment: 5 pages, 5 figure
Carbon Nanotubes as Nanoelectromechanical Systems
We theoretically study the interplay between electrical and mechanical
properties of suspended, doubly clamped carbon nanotubes in which charging
effects dominate. In this geometry, the capacitance between the nanotube and
the gate(s) depends on the distance between them. This dependence modifies the
usual Coulomb models and we show that it needs to be incorporated to capture
the physics of the problem correctly. We find that the tube position changes in
discrete steps every time an electron tunnels onto it. Edges of Coulomb
diamonds acquire a (small) curvature. We also show that bistability in the tube
position occurs and that tunneling of an electron onto the tube drastically
modifies the quantized eigenmodes of the tube. Experimental verification of
these predictions is possible in suspended tubes of sub-micron length.Comment: 8 pages, 5 eps figures included. Major changes; new material adde
Continuous variable entanglement by radiation pressure
We show that the radiation pressure of an intense optical field impinging on
a perfectly reflecting vibrating mirror is able to entangle in a robust way the
first two optical sideband modes. Under appropriate conditions, the generated
entangled state is of EPR type [A. Einstein, {\it et al.}, Phys. Rev. {\bf 47},
777 (1935)].Comment: 11 pages, 3 figure
Evaluating the extent of a large-scale transformation in gateway science courses
We evaluate the impact of an institutional effort to transform undergraduate science courses using an approach based on course assessments. The approach is guided by A Framework for K-12 Science Education and focuses on scientific and engineering practices, crosscutting concepts, and core ideas, together called three-dimensional learning. To evaluate the extent of change, we applied the Three-dimensional Learning Assessment Protocol to 4 years of chemistry, physics, and biology course exams. Changes in exams differed by discipline and even by course, apparently depending on an interplay between departmental culture, course organization, and perceived course ownership, demonstrating the complex nature of transformation in higher education. We conclude that while transformation must be supported at all organizational levels, ultimately, change is controlled by factors at the course and departmental levels
Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion
We perform a quantum theoretical calculation of the noise power spectrum for
a phase measurement of the light output from a coherently driven optical cavity
with a freely moving rear mirror. We examine how the noise resulting from the
quantum back action appears among the various contributions from other noise
sources. We do not assume an ideal (homodyne) phase measurement, but rather
consider phase modulation detection, which we show has a different shot noise
level. We also take into account the effects of thermal damping of the mirror,
losses within the cavity, and classical laser noise. We relate our theoretical
results to experimental parameters, so as to make direct comparisons with
current experiments simple. We also show that in this situation, the standard
Brownian motion master equation is inadequate for describing the thermal
damping of the mirror, as it produces a spurious term in the steady-state phase
fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi,
Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy.Comment: 12 pages revtex, 2 figure
Mirror quiescence and high-sensitivity position measurements with feedback
We present a detailed study of how phase-sensitive feedback schemes can be
used to improve the performance of optomechanical devices. Considering the case
of a cavity mode coupled to an oscillating mirror by the radiation pressure, we
show how feedback can be used to reduce the position noise spectrum of the
mirror, cool it to its quantum ground state, or achieve position squeezing.
Then, we show that even though feedback is not able to improve the sensitivity
of stationary position spectral measurements, it is possible to design a
nonstationary strategy able to increase this sensitivity.Comment: 25 pages, 11 figure
Quantum Measurement of a Single Spin using Magnetic Resonance Force Microscopy
Single-spin detection is one of the important challenges facing the
development of several new technologies, e.g. single-spin transistors and
solid-state quantum computation. Magnetic resonance force microscopy with a
cyclic adiabatic inversion, which utilizes a cantilever oscillations driven by
a single spin, is a promising technique to solve this problem. We have studied
the quantum dynamics of a single spin interacting with a quasiclassical
cantilever. It was found that in a similar fashion to the Stern-Gerlach
interferometer the quantum dynamics generates a quantum superposition of two
quasiclassical trajectories of the cantilever which are related to the two spin
projections on the direction of the effective magnetic field in the rotating
reference frame. Our results show that quantum jumps will not prevent a
single-spin measurement if the coupling between the cantilever vibrations and
the spin is small in comparison with the amplitude of the radio-frequency
external field.Comment: 16 pages RevTeX including 4 figure
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