959 research outputs found
Introducing Innovative Approaches in Business Schools
This half day workshop offered a selection of innovative approaches used in a UK, Dutch and Danish business School.
During the workshop participants explored what could work in their own cultural and institutional contexts
Stationary quantum Markov process for the Wigner function
As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde
Quantum Monte Carlo study of a magnetic-field-driven 2D superconductor-insulator transition
We numerically study the superconductor-insulator phase transition in a model
disordered 2D superconductor as a function of applied magnetic field. The
calculation involves quantum Monte Carlo calculations of the (2+1)D XY model in
the presence of both disorder and magnetic field. The XY coupling is assumed to
have the form -J\cos(\theta_i-\theta_j-A_{ij}), where A_{ij} has a mean of zero
and a standard deviation \Delta A_{ij}. In a real system, such a model would be
approximately realized by a 2D array of small Josephson-coupled grains with
slight spatial disorder and a uniform applied magnetic field. The different
values \Delta A_{ij} then corresponds to an applied field such that the average
number of flux quanta per plaquette has various integer values N: larger N
corresponds to larger \Delta A_{ij}. For any value of \Delta A_{ij}, there
appears to be a critical coupling constant K_c(\Delta
A_{ij})=\sqrt{[J/(2U)]_c}, where U is the charging energy, above which the
system is a Mott insulator; there is also a corresponding critical conductivity
\sigma^*(\Delta A_{ij}) at the transition. For \Delta A_{ij}=\infty, the order
parameter of the transition is a renormalized coupling constant g. Using a
numerical technique appropriate for disordered systems, we show that the
transition at this value of \Delta A_{ij} takes place from an insulating (I)
phase to a Bose glass (BG) phase, and that the dynamical critical exponent
characterizing this transition is z \sim 1.3. By contrast, z=1 for this model
at \Delta A_{ij}=0. We suggest that the superconductor to insulator transition
is actually of this I to BG class at all nonzero \Delta A_{ij}'s, and we
support this interpretation by both numerical evidence and an analytical
argument based on the Harris criterion.Comment: 17 pages, 23 figures, accepted for publication in Phys. Rev.
Spatially Resolved Excitation of Rydberg Atoms and Surface Effects on an Atom Chip
We demonstrate spatially resolved, coherent excitation of Rydberg atoms on an
atom chip. Electromagnetically induced transparency (EIT) is used to
investigate the properties of the Rydberg atoms near the gold coated chip
surface. We measure distance dependent shifts (~10 MHz) of the Rydberg energy
levels caused by a spatially inhomogeneous electric field. The measured field
strength and distance dependence is in agreement with a simple model for the
electric field produced by a localized patch of Rb adsorbates deposited on the
chip surface during experiments. The EIT resonances remain narrow (< 4 MHz) and
the observed widths are independent of atom-surface distance down to ~20 \mum,
indicating relatively long lifetime of the Rydberg states. Our results open the
way to studies of dipolar physics, collective excitations, quantum metrology
and quantum information processing involving interacting Rydberg excited atoms
on atom chips
Electrical control of spin dynamics in finite one-dimensional systems
We investigate the possibility of the electrical control of spin transfer in
monoatomic chains incorporating spin-impurities. Our theoretical framework is
the mixed quantum-classical (Ehrenfest) description of the spin dynamics, in
the spirit of the s-d-model, where the itinerant electrons are described by a
tight-binding model while localized spins are treated classically. Our main
focus is on the dynamical exchange interaction between two well-separated
spins. This can be quantified by the transfer of excitations in the form of
transverse spin oscillations. We systematically study the effect of an
electrostatic gate bias V_g on the interconnecting channel and we map out the
long-range dynamical spin transfer as a function of V_g. We identify regions of
V_g giving rise to significant amplification of the spin transmission at low
frequencies and relate this to the electronic structure of the channel.Comment: 9 pages, 11 figure
Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities
We present a method to analyze the suitability of particular photonic cavity
designs for information exchange between arbitrary superposition states of a
quantum emitter and the near-field photonic cavity mode. As an illustrative
example, we consider whether quantum dot emitters embedded in "L3" and "H1"
photonic crystal cavities are able to transfer a spin superposition state to a
confined photonic superposition state for use in quantum information transfer.
Using an established dyadic Green's function (DGF) analysis, we describe
methods to calculate coupling to arbitrary quantum emitter positions and
orientations using the modified local density of states (LDOS) calculated using
numerical finite-difference time-domain (FDTD) simulations. We find that while
superposition states are not supported in L3 cavities, the double degeneracy of
the H1 cavities supports superposition states of the two orthogonal modes that
may be described as states on a Poincar\'{e}-like sphere. Methods are developed
to comprehensively analyze the confined superposition state generated from an
arbitrary emitter position and emitter dipole orientation.Comment: 22 pages, 9 figure
Conditional phase shift from a quantum dot in a pillar microcavity
Large conditional phase shifts from coupled atom-cavity systems are a key
requirement for building a spin photon interface. This in turn would allow the
realisation of hybrid quantum information schemes using spin and photonic
qubits. Here we perform high resolution reflection spectroscopy of a quantum
dot resonantly coupled to a pillar microcavity. We show both the change in
reflectivity as the quantum dot is tuned through the cavity resonance, and
measure the conditional phase shift induced by the quantum dot using an ultra
stable interferometer. These techniques could be extended to the study of
charged quantum dots, where it would be possible to realise a spin photon
interface
Elevation in blood flow and shear rate prevents hyperglycemia-induced endothelial dysfunction in healthy subjects and those with type 2 diabetes
Hyperglycemia, commonly present after a meal, causes transient impairment in endothelial function. We examined whether increases in blood flow (BF) protect against the hyperglycemia- mediated decrease in endothelial function in healthy subjects and patients with type 2 diabetes mellitus (T2DM). Ten healthy subjects and 10 age- and sex-matched T2DM patients underwent simultaneous bilateral assessment of brachial artery endothelial function by means of flow- mediated dilation (FMD), using high-resolution echo-Doppler. FMD was examined before and 60, 120 and 150 minutes after a 75-gr oral glucose challenge. We unilaterally manipulated BF by heating one arm between minute 30 and 60. Oral glucose administration caused a statistically significant, transient increase in blood glucose in both groups (P<0.001). Forearm skin temperature, brachial artery BF and shear rate significantly increased in the heated arm (P<0.001), and to a greater extent compared to the non-heated arm in both groups (interaction- effect, P<0.001). The glucose load caused a transient decrease in FMD% (P<0.05), whilst heating significantly prevented the decline (interaction-effect: P<0.01). Also when correcting for changes in diameter and shear rate, we found that the hyperglycemia-induced decrease in FMD can be prevented by local heating (P<0.05). These effects on FMD were observed in both groups. Our data indicate that non-metabolically driven elevation in BF and shear rate can similarly prevent the hyperglycemia-induced decline in conduit artery endothelial function in healthy volunteers and in patients with type 2 diabetes. Additional research is warranted to confirm that other interventions increasing BF and shear rate equally protect the endothelium when challenged by hyperglycemia
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
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