2,363 research outputs found
Continuous quantum non-demolition measurement of Fock states of a nanoresonator using feedback-controlled circuit QED
We propose a scheme for the quantum non-demolition (QND) measurement of Fock
states of a nanomechanical resonator via feedback control of a coupled circuit
QED system. A Cooper pair box (CPB) is coupled to both the nanoresonator and
microwave cavity. The CPB is read-out via homodyne detection on the cavity and
feedback control is used to effect a non-dissipative measurement of the CPB.
This realizes an indirect QND measurement of the nanoresonator via a
second-order coupling of the CPB to the nanoresonator number operator. The
phonon number of the Fock state may be determined by integrating the stochastic
master equation derived, or by processing of the measurement signal.Comment: 5 pages, 3 figure
Modelling biological invasions: individual to population scales at interfaces
Extracting the population level behaviour of biological systems from that of the individual is critical in understanding dynamics across multiple scales and thus has been the subject of numerous investigations. Here, the influence of spatial heterogeneity in such contexts is explored for interfaces with a separation of the length scales characterising the individual and the interface, a situation that can arise in applications involving cellular modelling. As an illustrative example, we consider cell movement between white and grey matter in the brain which may be relevant in considering the invasive dynamics of glioma. We show that while one can safely neglect intrinsic noise, at least when considering glioma cell invasion, profound differences in population behaviours emerge in the presence of interfaces with only subtle alterations in the dynamics at the individual level. Transport driven by local cell sensing generates predictions of cell accumulations along interfaces where cell motility changes. This behaviour is not predicted with the commonly used Fickian diffusion transport model, but can be extracted from preliminary observations of specific cell lines in recent, novel, cryo-imaging. Consequently, these findings suggest a need to consider the impact of individual behaviour, spatial heterogeneity and especially interfaces in experimental and modelling frameworks of cellular dynamics, for instance in the characterisation of glioma cell motility
Count three for wear able computers
This paper is a postprint of a paper submitted to and accepted for publication in the Proceedings of the IEE Eurowearable 2003 Conference, and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.
A revised version of this paper was also published in Electronics Systems and Software, also subject to Institution of Engineering and Technology Copyright. The copy of record is also available at the IET Digital Library.A description of 'ubiquitous computer' is presented. Ubiquitous computers imply portable computers embedded into everyday objects, which would replace personal computers. Ubiquitous computers can be mapped into a three-tier scheme, differentiated by processor performance and flexibility of function. The power consumption of mobile devices is one of the most important design considerations. The size of a wearable system is often a design limitation
Rotational Effects of Twisted Light on Atoms Beyond the Paraxial Approximation
The transition probability for the emission of a Bessel photon by an atomic
system is calculated within first order perturbation theory. We derive a closed
expression for the electromagnetic potentials beyond the paraxial approximation
that permits a systematic multipole approximation . The matrix elements between
center of mass and internal states are evaluated for some specially relevant
cases. This permits to clarify the feasibility of observing the rotational
effects of twisted light on atoms predicted by the calculations. It is shown
that the probability that the internal state of an atom acquires orbital
angular momentum from light is, in general, maximum for an atom located at the
axis of a Bessel mode. For a Gaussian packet, the relevant parameter is the
ratio of the spread of the atomic center of mass wave packet to the transversal
wavelength of the photon.Comment: 10 pages, no figure
Long wavelength optical control of glutamate receptor ion channels using a tetra-ortho-substituted azobenzene derivative
A tetra-ortho-chloro substituted azobenzene unit was incorporated into a photoswitchable tethered ligand for ionotropic glutamate receptors. This compound confers the modified protein with the unusual optical responses of the substituted azo scaffold permitting channel opening with yellow and red light and channel closing with blue light
Nanomechanical squeezing with detection via a microwave cavity
We study a parametrically driven nanomechanical resonator capacitively coupled to a microwave cavity. If the nanoresonator can be cooled to near its quantum ground state then quantum squeezing of a quadrature of the nanoresonator motion becomes feasible. We consider the adiabatic limit in which the cavity mode is slaved to the nanoresonator mode. By driving the cavity on its red-detuned sideband, the squeezing can be coupled into the microwave field at the cavity resonance. The red-detuned sideband drive is also compatible with the goal of ground state cooling. Squeezing of the output microwave field may be inferred using a technique similar to that used to infer squeezing of the field produced by a Josephson parametric amplifier, and subsequently, squeezing of the nanoresonator motion may be inferred. We have calculated the output field microwave squeezing spectra and related this to squeezing of the nanoresonator motion, both at zero and finite temperature. Driving the cavity on the blue-detuned sideband, and on both the blue and red sidebands, have also been considered within the same formalism
On the Quantum Theory of Molecules
Transition state theory was introduced in the 1930s to account for chemical
reactions. Central to this theory is the idea of a potential energy surface
(PES). It was assumed that such a surface could be constructed using
eigensolutions of the Schr\"{o}dinger equation for the molecular (Coulomb)
Hamiltonian but at that time such calculations were not possible. Nowadays
quantum mechanical ab-initio electronic structure calculations are routine and
from their results PESs can be constructed which are believed to approximate
those assumed derivable from the eigensolutions. It is argued here that this
belief is unfounded. It is suggested that the potential energy surface
construction is more appropriately regarded as a legitimate and effective
modification of quantum mechanics for chemical purpose
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