5,188 research outputs found
Dispersive properties and giant Kerr non-linearities in Dipole Induced Transparency
We calculate the dispersive properties of the reflected field from a cavity
coupled to a single dipole. We show that when a field is resonant with the
dipole it experiences a 90 degree phase shift relative to reflection from a
bare cavity if the Purcell factor exceeds the bare cavity reflectivity. We then
show that optically Stark shifting the dipole with a second field can be used
to achieve giant Kerr non-linearites. It is shown that currently achievable
cavity lifetimes and cavity quality factors can allow a single emitter in the
cavity to impose a nonlinear phase shift at the single photon level
Economic Policy and Food Security in Ethiopia
Ethiopia has an integrated approach to addressing nutrition. However, greater clarity is needed on the wider impact of policy on food and nutrition. We focus on the interrelationship between economic policy and nutrition policy (defined as including all food- and nutrition-relevant policy). While Ethiopia’s policy has had notable successes, particularly with addressing stunting, two key challenges remain. First, some indicators such as wasting and anaemia in children under five have shown far less improvement. Second, the bottom quintile of children has seen far more limited general improvement than the population as a whole. We argue that the focus of government policy needs to shift from food availability to broader issues of food acquisition and particularly food affordability, which is mediated through food prices and waged employment. Of particular concern is the rising price of animal-source products and other non-staple foods, which may be related to the challenges of addressing some nutritional indicators
Collapse-revival dynamics and atom-field entanglement in the non-resonant Dicke model
We consider the dynamics of atomic and field coherent states in the
non-resonant Dicke model. At weak coupling an initial product state evolves
into a superposition of multiple field coherent states that are correlated with
the atomic configuration. This process is accompanied by the buildup and decay
of atom-field entanglement and leads to the periodic collapse and revival of
Rabi oscillations. We provide a perturbative derivation of the underlying
dynamical mechanism that complements the rotating wave approximation at
resonance. The identification of two different time scales explains how the
dynamical signatures depend on the sign of detuning between the atomic and
field frequency, and predicts the generation of either atomic or field cat
states in the two opposite cases. We finally discuss the restrictions that the
buildup of atom-field entanglement during the collapse of Rabi oscillations
imposes on the validity of semi-classical approximations that neglect
entanglement.Comment: 9 pages, 10 figures. Published versio
An assessment of the construct validity of environmental strategy measures
The natural resource-based view of the company is emerging as a dominant paradigm for understanding the intersection of strategic management and the natural environment. Companies that proactively incorporate a natural environment perspective into their enterprise strategies are said to have sustainable competitive advantages. However, defining and measuring environmental strategy has been challenging, with different approaches yielding inconsistent results. Many studies ignore the empirical difficulties of marrying the theoretical connection between the company's resource base and environmental strategy, and its impact on environmental company performance. In this paper, we apply an inductive approach to derive a measure of environmental strategy theoretically congruent with the natural resource-based-view of the firm. We assess its reliability and, using a multi-trait multi-method matrix, confirm the convergent and discriminant validities of this measure against other measures often used by researchers. We also establish predictive validity of our environmental strategy measure for environmental performance. We discuss the implications of the measure for future research and practice.environmental performance; environmental strategies; inductive study; measures;
Quantification of Macroscopic Quantum Superpositions within Phase Space
Based on phase-space structures of quantum states, we propose a novel measure
to quantify macroscopic quantum superpositions. Our measure simultaneously
quantifies two different kinds of essential information for a given quantum
state in a harmonious manner: the degree of quantum coherence and the effective
size of the physical system that involves the superposition. It enjoys
remarkably good analytical and algebraic properties. It turns out to be the
most general and inclusive measure ever proposed that it can be applied to any
types of multipartite states and mixed states represented in phase space.Comment: 4 pages, 1 figure, accepted for publication in Phys. Rev. Let
A Model for the Production of Regular Fluorescent Light from Coherently Driven Atoms
It has been shown in recent years that incoherent pumping through multiple
atomic levels provides a mechanism for the production of highly anti-bunched
light, and that as the number of incoherent steps is increased the light
becomes increasingly regular. We show that in a resonance fluorescence
situation, a multi-level atom may be multiply coherently driven so that the
fluorescent light is highly anti-bunched. We show that as the number of
coherently driven levels is increased, the spontaneous emissions may be made
increasingly more regular. We present a systematic method for designing the
level structure and driving required to produce highly anti-bunched light in
this manner for an arbitrary even number of levels.Comment: 6 pages multicol revtex, including figure
Dicke quantum spin glass of atoms and photons
Recent studies of strongly interacting atoms and photons in optical cavities
have rekindled interest in the Dicke model of atomic qubits coupled to discrete
photon cavity modes. We study the multimode Dicke model with variable
atom-photon couplings. We argue that a quantum spin glass phase can appear,
with a random linear combination of the cavity modes superradiant. We compute
atomic and photon spectral response functions across this quantum phase
transition, both of which should be accessible in experiment.Comment: 4 pages, 3 figures, v2: described quantum optics set-up in more
detail; extended discussion on photon correlation functions and experimental
signatures; added reference
Shaping an Itinerant Quantum Field by Dissipation
We show that inducing sidebands in the emission of a single emitter into a
one dimensional waveguide, together with a dissipative re-pumping process, a
photon field is cooled down to a squeezed vacuum. Our method does not require
to be in the strong coupling regime, works with a continuum of propagating
field modes and it may lead to sources of tunable multimode squeezed light in
circuit QED systems.Comment: 4 pages, 3 figure
Viewpoint: Separating the Science and Politics of “Obesity”
Last month, JAMA published a systematic review and meta-analysis of the relationship between body mass index (BMI) and all-cause mortality. The researchers, led by Katherine M. Flegal, PhD, of the US Centers for Disease Control and Prevention, found that people who are categorized as being mildly obese according to their BMI had no increased risk of dying prematurely, and overweight people a slightly reduced risk of dying prematurely, compared with their normal-weight counterparts—a finding supported by previous studies. In an accompanying editorial, 2 researchers said that the findings highlighted the limitations of increased BMI as an indicator of unhealthiness. Early coverage of the study in the mass media was restrained, emphasizing the authors’ main messages. Response in social media such as Twitter ranged from excited acceptance to confusion and voicing of familiar critiques, such as the limitations of observational studies or of using all-cause mortality as an outcome measure rather than morbidity or disability. And then the response evolved and became heated.NHMR
Relationships Between the Performance of Time/Frequency Standards and Navigation/Communication Systems
The relationship between system performance and clock or oscillator performance is discussed. Tradeoffs discussed include: short term stability versus bandwidth requirements; frequency accuracy versus signal acquisition time; flicker of frequency and drift versus resynchronization time; frequency precision versus communications traffic volume; spectral purity versus bit error rate, and frequency standard stability versus frequency selection and adjustability. The benefits and tradeoffs of using precise frequency and time signals are various levels of precision and accuracy are emphasized
- …