Conditional phase shifts using trapped atoms

We describe a scheme for producing conditional nonlinear phase shifts on two-photon optical fields using an interaction with one or more ancilla two-level atomic systems. The conditional field state transformations are induced by using high efficiency fluorescence shelving measurements on the atomic ancilla. The scheme can be nearly deterministic and is of obvious benefit for quantum information applications

A participatory action research study of key account management changes

Pure Participatory Action Research projects in the IMP research tradition are rather rare. This paper describes both the process and the outcomes of such a project carried out for a major business to retail firm in the UK. The issue at hand was, and is, Key Account Management, defined in a very broad way. The process is one of changing the ways in which the actors in the firm at different levels work together to try to coordinate the long term strategy and short term operations in relation to powerful retail customers. The outcomes for the firm have, so far, been very positive. The outcomes for the researchers are too early to fully evaluate but look very promising

Critical decay index at the onset of solar eruptions

Magnetic flux ropes are topological structures consisting of twisted magnetic field lines that globally wrap around an axis. The torus instability model predicts that a magnetic flux rope of major radius $R$ undergoes an eruption when its axis reaches a location where the decay index $-d(\ln B_{ex})/d(\ln R)$ of the ambient magnetic field $B_{ex}$ is larger than a critical value. In the current-wire model, the critical value depends on the thickness and time-evolution of the current channel. We use magneto-hydrodynamic (MHD) simulations to investigate if the critical value of the decay index at the onset of the eruption is affected by the magnetic flux rope's internal current profile and/or by the particular pre-eruptive photospheric dynamics. The evolution of an asymmetric, bipolar active region is driven by applying different classes of photospheric motions. We find that the critical value of the decay index at the onset of the eruption is not significantly affected by either the pre-eruptive photospheric evolution of the active region or by the resulting different magnetic flux ropes. As in the case of the current-wire model, we find that there is a `critical range' $[1.3-1.5]$, rather than a `critical value' for the onset of the torus instability. This range is in good agreement with the predictions of the current-wire model, despite the inclusion of line-tying effects and the occurrence of tether-cutting magnetic reconnection.Comment: 15 pages, 9 figures. To appear in The Astrophysical Journa

Signatures of the Pair-Coherent State

We explore in detail the possibility of generating a pair-coherent state in the non-degenerate parametric oscillator when decoherence is included. Such states are predicted in the transient regime in parametric oscillation where the pump mode is adiabatically eliminated. Two specific signatures are examined to indicate whether the state of interest has been generated, the Schrodinger cat state - like signatures, and the fidelity. Solutions in a transient regime reveal interference fringes which are indicative of the formation of a Schrodinger cat state. The fidelity indicates the purity of our prepared state compared to the ideal pair-coherent state.Comment: Figures hacked down to size for serve

Quantum computation with optical coherent states

We show that quantum computation circuits using coherent states as the logical qubits can be constructed from simple linear networks, conditional photon measurements and "small" coherent superposition resource states

Impact of Waste Heat on Simulated Climate: A Megalopolis Scenario

The general circulation model (GCM) of the Meteorological Office (NO), U.K., was used to investigate the impact of waste heat on simulated global climate. These experiments are a further set in a series of experiments made to investigate the behavior of the simulated circulation with different scenarios and energy releases. In contrast to the previous experiments, the heat is distributed only over continental areas, where large energy and/or population densities can be expected in the future. The results suggest that the atmosphere responds very sensitively to the distribution of the heat input. Although the total hemispheric changes are smaller than in some of the previous experiments, there are still considerable areas where the difference between the perturbed model run and the control cases is large compared with the inherent variability of the model

Further Studies of the Impact of Waste Heat Release on Simulated Global Climate: Part I

The general circulation model (GCM) of the United Kingdom Meteorological Office (UKMO) has been used to investigate the impact of an input of waste heat (1.5 x 10e14 watts) into the atmosphere in a small area in the mid-latitude eastern Atlantic Ocean. The results of this experiment have been compared with those of two earlier experiments in which the waste heat was input from two energy parks, one in the Atlantic and one in the Pacific Ocean. The energy park produced significant responses in the surface pressure field, the temperature in the lowest layer of the model, and in the total precipitation distribution. The changes are of the same order of magnitude as the changes found in two earlier energy park experiments, and there are some similarities between changes in this experiment and EX01, especially over the area immediately downstream of the energy park. The results of all three energy park experiments have been investigated using zonal harmonic analysis, and the influence of the energy parks on the positions and amplitudes of waves in the temperature and wind fields are discussed

Time-reversal and super-resolving phase measurements

We demonstrate phase super-resolution in the absence of entangled states. The key insight is to use the inherent time-reversal symmetry of quantum mechanics: our theory shows that it is possible to \emph{measure}, as opposed to prepare, entangled states. Our approach is robust, requiring only photons that exhibit classical interference: we experimentally demonstrate high-visibility phase super-resolution with three, four, and six photons using a standard laser and photon counters. Our six-photon experiment demonstrates the best phase super-resolution yet reported with high visibility and resolution.Comment: 4 pages, 3 figure

Improving the entanglement transfer from continuous variable systems to localized qubits using non Gaussian states

We investigate the entanglement transfer from a bipartite continuous-variable (CV) system to a pair of localized qubits assuming that each CV mode couples to one qubit via the off-resonance Jaynes-Cummings interaction with different interaction times for the two subsystems. First, we consider the case of the CV system prepared in a Bell-like superposition and investigate the conditions for maximum entanglement transfer. Then we analyze the general case of two-mode CV states that can be represented by a Schmidt decomposition in the Fock number basis. This class includes both Gaussian and non Gaussian CV states, as for example twin-beam (TWB) and pair-coherent (TMC, also known as two-mode-coher ent) states respectively. Under resonance conditions, equal interaction times for both qubits and different initial preparations, we find that the entanglement transfer is more efficient for TMC than for TWB states. In the perspective of applications such as in cavity QED or with superconducting qubits, we analyze in details the effects of off-resonance interactions (detuning) and different interaction times for the two qubits, and discuss conditions to preserve the entanglement transfer.Comment: revised version, 11 pages, 7 figures (few of them low-res