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 $\pi$ 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