Quantum Nonlocality for a Mixed Entangled Coherent State

Quantum nonlocality is tested for an entangled coherent state, interacting with a dissipative environment. A pure entangled coherent state violates Bell's inequality regardless of its coherent amplitude. The higher the initial nonlocality, the more rapidly quantum nonlocality is lost. The entangled coherent state can also be investigated in the framework of $2\times2$ Hilbert space. The quantum nonlocality persists longer in $2\times2$ Hilbert space. When it decoheres it is found that the entangled coherent state fails the nonlocality test, which contrasts with the fact that the decohered entangled state is always entangled.Comment: 20 pages, 7 figures. To be published in J. Mod. Op

Overcoming decoherence in the collapse and revival of spin Schr\"odinger cats

In addition to being a very interesting quantum phenomenon, Schr\"odinger cat swapping has the potential for application in the preparation of quantum states that could be used in metrology and other quantum processing. We study in detail the effects of field decoherence on a cat-swapping system comprising a set of identical qubits, or spins, all coupled to a field mode. We demonstrate that increasing the number of spins actually mitigates the effects of field decoherence on the collapse and revival of a spin Schr\"odinger cat, which could be of significant utility in quantum metrology and other quantum processing.Comment: 4 pages, 2 figure

Non-Markovian dynamics of a qubit

In this paper we investigate the non-Markovian dynamics of a qubit by comparing two generalized master equations with memory. In the case of a thermal bath, we derive the solution of the post-Markovian master equation recently proposed in Ref. [A. Shabani and D.A. Lidar, Phys. Rev. A {\bf 71}, 020101(R) (2005)] and we study the dynamics for an exponentially decaying memory kernel. We compare the solution of the post-Markovian master equation with the solution of the typical memory kernel master equation. Our results lead to a new physical interpretation of the reservoir correlation function and bring to light the limits of usability of master equations with memory for the system under consideration.Comment: Replaced with published version (minor changes

Limits in the characteristic function description of non-Lindblad-type open quantum systems

In this paper I investigate the usability of the characteristic functions for the description of the dynamics of open quantum systems focussing on non-Lindblad-type master equations. I consider, as an example, a non-Markovian generalized master equation containing a memory kernel which may lead to nonphysical time evolutions characterized by negative values of the density matrix diagonal elements [S.M. Barnett and S. Stenholm, Phys. Rev. A {\bf 64}, 033808 (2001)]. The main result of the paper is to demonstrate that there exist situations in which the symmetrically ordered characteristic function is perfectly well defined while the corresponding density matrix loses positivity. Therefore nonphysical situations may not show up in the characteristic function. As a consequence, the characteristic function cannot be considered an {\it alternative complete} description of the non-Lindblad dynamics.Comment: Revised version. 4 pages, 1 figur

Experiences of aspiring school principals receiving coaching as part of a leadership development programme

Purpose This paper adds depth to our understanding of how coaching works by exploring the experiences of 14 aspiring school principals who received one-to-one leadership coaching as part of a leadership development programme. Design/methodology/approach This study adopts a phenomenological approach. Individual semi-structured interviews were conducted with the participants. Thematic analysis was used to code the data and identify themes. Findings This paper reports on four themes based on the experiences of the participants: having time to reflect, feeling safe to explore, focussing on what's important for me and experiencing positive emotions. Research limitations/implications The findings are unique to the participants who volunteered to take part in this study and therefore not representative of a general population of aspiring educational leaders. Further research is needed into the possible benefits of coaching to support educators undergoing leadership training. Practical implications The findings raise a potential dilemma within the teaching profession about the use of educators' time; while they need to give time and attention to multiple stakeholders, they also need to protect time for their own development and self-reflection. Based on the reported experiences of the participants in this study, it is recommended that coaching be considered a component of professional development for educational leaders. Originality/value This paper adds to the growing research base for coaching in education, providing a unique insight into the experiences of aspiring school principals who received one-to-one leadership coaching as part of a leadership development programme

Ensemble averaged entanglement of two-particle states in Fock space

Recent results, extending the Schmidt decomposition theorem to wavefunctions of identical particles, are reviewed. They are used to give a definition of reduced density operators in the case of two identical particles. Next, a method is discussed to calculate time averaged entanglement. It is applied to a pair of identical electrons in an otherwise empty band of the Hubbard model, and to a pair of bosons in the the Bose-Hubbard model with infinite range hopping. The effect of degeneracy of the spectrum of the Hamiltonian on the average entanglement is emphasised.Comment: 19 pages Latex, changed title, references added in the conclusion

Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence

Here, we report laboratory experiments to investigate the threshold criteria for incipient sediment motion in the presence of oscillating-grid turbulence, with the bed slope inclined at angles between the horizontal and the repose limit for the sediment. A set of nine mono-disperse sediment types was used with size ranges normally associated with either the hydraulically-smooth or transitional regimes. Measurements of the (turbulent) fluid velocity field, in the region between the grid and bedform's surface, were obtained using two-dimensional particle imaging velocimetry. Statistical analysis of the velocity data showed that the turbulence had a anisotropic structure, due to the net transfer of energy from the normal to the tangential velocity components in the near-bed region, and that the fluctuations were dominant compared to the secondary mean flow. The sediment threshold criteria for horizontal bedforms were compared with, and found to be in good qualitative agreement with the standard Shields curve. For non-horizontal bedforms, the bed mobility was found to increase with increasing bed slope, and the threshold criteria were compared with previously-reported theoretical models, based on simple force-balance arguments

The PKC, HOG and Ca2+ signalling pathways co-ordinately regulate chitin synthesis in Candida albicans

Open Access via PMC2649417Peer reviewedPublisher PD