Comment on "General Non-Markovian Dynamics of Open Quantum Systems"

The existence of a "non-Markovian dissipationless" regime, characterized by long lived oscillations, was recently reported for a class of quantum open systems (Zhang et al, PRL, 109, 170402, (2012)). It is claimed this could happen in the strong coupling regime, a surprising result which has attracted some attention. We show that this regime exists if and only if the total Hamiltonian is unbounded from below, casting serious doubts on the usefulness of this result

Phase Estimation With Interfering Bose-Condensed Atomic Clouds

We investigate how to estimate from atom-position measurements the relative phase of two Bose-Einstein condensates released from a double-well potential. We demonstrate that the phase estimation sensitivity via the fit of the average density to the interference pattern is fundamentally bounded by shot noise. This bound can be overcome by estimating the phase from the measurement of $\sqrt N$ (or higher) correlation function. The optimal estimation strategy requires the measurement of the $N$-th order correlation function. We also demonstrate that a second estimation method -- based on the detection of the center of mass of the interference pattern -- provides sub shot-noise sensitivity. Yet, the implementation of both protocols might be experimentally challenging.Comment: 4 pages, 2 figure

eFRIEND: an ethical framework for intelligent environments development

Intelligent environments aim to provide context-sensitive services to humans in the physical spaces in which they work and live. While the ethical dimensions of these systems have been considered, this is an aspect which requires further analysis. A literature review shows that these approaches are disconnected from each other, and that they are making little impact on real systems being built. This article provides a solution to both of these problems. It synthesises the ethical issues addressed by previous work and highlights other important concerns which have been overlooked so far. Furthermore, it proposes an alternative, more holistic approach that can be used to guide the development of intelligent environments. The validity of the framework is demonstrated by its integration into an actual project

eFRIEND: an ethical framework for intelligent environment development

Intelligent Environments bring technology closer to daily life and aim to provide context-sensitive services to humans in the physical spaces in which they work and live. Some developments have considered the ethical dimension of these systems; however this is an aspect, which requires further analysis. A literature review shows that these approaches are rather disconnected from each other, and that they are not making an impact on real systems being built. This paper summarises the ethical concerns addressed by previous work, highlights other important concerns, which have been overlooked so far, and proposes a more holistic approach. It explains how these concerns can be used to guide part of the development process in such a way that Intelligent Environments being engineered in the future will consider the ethical dimension in practice, not just in theory

Photon emission as a source of coherent behaviour of polaritons

We show that the combined effect of photon emission and Coulomb interactions may drive an exciton-polariton system towards a dynamical coherent state, even without phonon thermalization or any other relaxation mechanism. Exact diagonalization results for a finite system (a multilevel quantum dot interacting with the lowest energy photon mode of a microcavity) are presented in support to this statement

Mach-Zehnder interferometry with interacting trapped Bose-Einstein condensates

We theoretically analyze a Mach-Zehnder interferometer with trapped condensates, and find that it is surprisingly stable against the nonlinearity induced by inter-particle interactions. The phase sensitivity, which we study for number squeezed input states, can overcome the shot noise limit and be increased up to the Heisenberg limit provided that a Bayesian or Maximum-Likelihood phase estimation strategy is used. We finally demonstrate robustness of the Mach-Zehnder interferometer in presence of interactions against condensate oscillations and a realistic atom counting error.Comment: 4 pages, 5 figures, minor revision

Entanglement, Non-linear Dynamics, and the Heisenberg Limit

We show that the quantum Fisher information provides a sufficient condition to recognize multi-particle entanglement in a $N$ qubit state. The same criterion gives a necessary and sufficient condition for sub shot-noise phase sensitivity in the estimation of a collective rotation angle $\theta$. The analysis therefore singles out the class of entangled states which are {\it useful} to overcome classical phase sensitivity in metrology and sensors. We finally study the creation of useful entangled states by the non-linear dynamical evolution of two decoupled Bose-Einstein condensates or trapped ions.Comment: Phys. Rev. Lett. 102, 100401 (2009