Pulse retrieval and soliton formation in a non-standard scheme for dynamic electromagnetically induced transparency

We examine in detail an alternative method of retrieving the information written into an atomic ensemble of three-level atoms using electromagnetically induced transparency. We find that the behavior of the retrieved pulse is strongly influenced by the relative collective atom-light coupling strengths of the two relevant transitions. When the collective atom-light coupling strength for the retrieval beam is the stronger of the two transitions, regeneration of the stored pulse is possible. Otherwise, we show the retrieval process can lead to creation of soliton-like pulses.Comment: 11 figure

Outcoupling from a Bose-Einstein condensate with squeezed light to produce entangled atom laser beams

We examine the properties of an atom laser produced by outcoupling from a Bose-Einstein condensate with squeezed light. We model the multimode dynamics of the output field and show that a significant amount of squeezing can be transfered from an optical mode to a propagating atom laser beam. We use this to demonstrate that two-mode squeezing can be used to produce twin atom laser beams with continuous variable entanglement in amplitude and phase.Comment: 11 pages, 14 figure

Quantum depletion of collapsing Bose-Einstein condensates

We perform the first numerical three-dimensional studies of quantum field effects in the Bosenova experiment on collapsing condensates by E. Donley et al. [Nature 415, 39 (2002)] using the exact experimental geometry. In a stochastic truncated Wigner simulation of the collapse, the collapse times are larger than the experimentally measured values. We find that a finite temperature initial state leads to an increased creation rate of uncondensed atoms, but not to a reduction of the collapse time. A comparison of the time-dependent Hartree-Fock-Bogoliubov and Wigner methods for the more tractable spherical trap shows excellent agreement between the uncondensed populations. We conclude that the discrepancy between the experimental and theoretical values of the collapse time cannot be explained by Gaussian quantum fluctuations or finite temperature effects.Comment: 9 pages, 4 figures, replaced with published versio

Exact solution, scaling behaviour and quantum dynamics of a model of an atom-molecule Bose-Einstein condensate

We study the exact solution for a two-mode model describing coherent coupling between atomic and molecular Bose-Einstein condensates (BEC), in the context of the Bethe ansatz. By combining an asymptotic and numerical analysis, we identify the scaling behaviour of the model and determine the zero temperature expectation value for the coherence and average atomic occupation. The threshold coupling for production of the molecular BEC is identified as the point at which the energy gap is minimum. Our numerical results indicate a parity effect for the energy gap between ground and first excited state depending on whether the total atomic number is odd or even. The numerical calculations for the quantum dynamics reveals a smooth transition from the atomic to the molecular BEC.Comment: 5 pages, 4 figure

Relationship between Youth and Parent Perceptions of Family Environment and Social Anxiety

This study concurrently examined the relationship between adolescents’ perceptions of their parents’ child-rearing styles and family environment and their reports of social anxiety. Adolescents reporting higher levels of social anxiety perceived their parents as being more socially isolating, overly concerned about others’ opinions, ashamed of their shyness and poor performance, and less socially active than did youth reporting lower levels of social anxiety. Parent perceptions of child-rearing styles and family environment, however, did not differ between parents of socially anxious and nonsocially anxious adolescents. Results are comparable to studies using adult retrospective reports and are discussed with regard to the role of the family environment in the development of social anxiety

Nanocrystallization and Amorphization Induced by Reactive Nitrogen Sputtering in Iron and Permalloy

Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron sputtering technique at ambient temperature. The nitrogen partial pressure, during sputtering process was varied in the range of 0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an increase in nitrogen partail pressure results in formation of an amorphous structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe were obtained while at even higher nitrogen partial pressures, nitrides themselves became nanocrystalline or amorphous. The surface, structural and magnetic properties of the deposited films were studied using x-ray reflection and diffraction, transmission electron microscopy, polarized neutron reflectivity and using a DC extraction magnetometer. The growth behavior for amorphous film was found different as compared with poly or nanocrystalline films. The soft-magnetic properties of FeN were improved on nanocrystallization while those of NiFeN were degraded. A mechanism inducing nanocrystallization and amorphization in Fe and NiFe due to reactive nitrogen sputtering is discussed in the present article.Comment: 13 Pages, 15 Figure

Making Space for the Dissertation : a Rural Retreat for Undergraduate Students

This paper examines a residential writing retreat for final year human geography and planning students held in a youth hostel in North Yorkshire, considering how it is experienced by students. This is a curriculum innovation for the dissertation module that combines aspects of geography fieldtrip and writing workshop to support the dissertation writing process and build community. Drawing on the concept of ‘the slow university’ (Berg & Seeber, 2016; O’Neill, 2014) where the ‘slowing down’ and ‘stripping away’ of the usual structures and patterns of teaching and learning create a critical and creative space for thinking and writing, we explore whether and how the Malham retreat makes space for writing. The study is also informed by our spatial approach to the processes and content of research and teaching as geographers (Massey, 2005). Qualitative focus group evidence was gathered on the student and staff experience and used to evaluate the field trip (Breen, 2006; Krueger & Casey, 2009; Stewart & Shamdasani, 2015). This paper presents the results of this evaluation and it is argued that the retreat made space for writing in three ways: 1. The space of countryside, nature and youth hostel. 2. The formal and informal learning spaces staff and students constructed during the retreat 3. ‘Head space’- the social, psychological and emotional room the retreat made for staff and students. This model of residential writing retreat could be transferable to dissertation and other modules involving a substantive writing project on all kinds of undergraduate courses