9 research outputs found
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Decay rates and energies of free magnons and bound states in dissipative XXZ chains
Chains of coupled two-level atoms behave as 1D quantum spin systems,
exhibiting free magnons and magnon bound states. While these excitations are
well studied for closed systems, little consideration has been given to how
they are altered by the presence of an environment. This will be especially
important in systems that exhibit nonlocal dissipation, e.g. systems in which
the magnons decay due to optical emission. In this work, we consider free
magnon excitations and two-magnon bound states in an XXZ chain with nonlocal
dissipation. We prove that whilst the energy of the bound state can lie outside
the two-magnon continuum of energies, the decay rate of the bound state has to
always lie within the two-magnon continuum of decay rates. We then derive
analytically the bound state solutions for a system with nearest-neighbour and
next-nearest-neighbour XY interaction and nonlocal dissipation, finding that
the inclusion of nonlocal dissipation allows more freedom in engineering the
energy and decay rate dispersions for the bound states. Finally, we numerically
study a model of an experimental set-up that should allow the realisation of
dissipative bound states by using Rydberg-dressed atoms coupled to a photonic
crystal waveguide (PCW). We demonstrate that this model can exhibit many key
features of our simpler models
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Steady states of a driven dissipative dipolar XXZ chain
We study theoretically a driven dissipative one-dimensional XXZ spin
chain with dipole coupling and a tunable strength of the Ising and XY
interaction. Within a mean-field approximation, we find a rich phase diagram
with uniform, spin density wave, antiferromagnetic and oscillatory phases, as
well as regions of phase bistability. We study the phase diagram of small
quantum systems using exact diagonalisation, and compare the results to the
mean-field theory. We find that while expectation values only capture the
uniform phases of the mean-field theory, fluctuations about these expectation
values give signatures of spatially non-uniform phases and bistabilities. We
find these signatures for all ratios of the Ising to XY interaction, showing
that they appear to be general features of spin system
Stable collective dynamics of two-level systems coupled by dipole interactions
We study the dynamics of a set of two-level systems coupled by dipolar interactions under a resonant external Rabi drive. The two-level systems are prepared initially in a coherent product state, and we ask how the nonequilibrium conditions caused by the drive affect this coherence. We study the full nonlinear dynamics of the coupled two-level systems within a classical approximation by analyzing numerically the equations of motion and determining the stability of the collective coherent state within classical Floquet theory. We establish the behavior analytically in the high Rabi coupling limit by employing a Magnus expansion and spin-wave analysis. Our results show that, typically, the dipole interactions between the two-level systems lead to instabilities that cause a breakdown of the collective Rabi oscillations. However, we identify parameter regimes for which the two-level systems undergo collective coherent Rabi oscillations even in the presence of the dipole interactions.This work was supported by EPSRC Grant No. EP/K030094/1
On the role of individual human abilities in the design of adaptive user interfaces for scientific problem solving environments
Small molecules enhance CRISPR/Cas9-mediated homology-directed genome editing in primary cells
On the role of individual human abilities in the design of adaptive user interfaces for scientific problem solving environments
A scientific problem solving environment should be built in such a way that users (scientists) might exploit underlying technologies without a specialised knowledge about available tools and resources. An adaptive user interface can be considered as an opportunity in addressing this challenge. This paper explores the importance of individual human abilities in the design of adaptive user interfaces for scientific problem solving environments. In total, seven human factors (gender, learning abilities, locus of control, attention focus, cognitive strategy and verbal and nonverbal IQs) have been evaluated regarding their impact on interface adjustments done manually by users. People’s preferences for different interface configurations have been investigated. The experimental study suggests criteria for the inclusion of human factors into the user model guiding and controlling the adaptation process. To provide automatic means of adaptation, the Intelligent System for User Modelling has been developed