1,867 research outputs found
Continuous phase-space representations for finite-dimensional quantum states and their tomography
Continuous phase spaces have become a powerful tool for describing,
analyzing, and tomographically reconstructing quantum states in quantum optics
and beyond. A plethora of these phase-space techniques are known, however a
thorough understanding of their relations was still lacking for
finite-dimensional quantum states. We present a unified approach to continuous
phase-space representations which highlights their relations and tomography.
The infinite-dimensional case from quantum optics is then recovered in the
large-spin limit.Comment: 15 pages, 9 figures, v4: extended tomography analysis, added
references and figure
Controlling Several Atoms in a Cavity
We treat control of several two-level atoms interacting with one mode of the
electromagnetic field in a cavity. This provides a useful model to study
pertinent aspects of quantum control in infinite dimensions via the emergence
of infinite-dimensional system algebras. Hence we address problems arising with
infinite-dimensional Lie algebras and those of unbounded operators. For the
models considered, these problems can be solved by splitting the set of control
Hamiltonians into two subsets: The first obeys an abelian symmetry and can be
treated in terms of infinite-dimensional Lie algebras and strongly closed
subgroups of the unitary group of the system Hilbert space. The second breaks
this symmetry, and its discussion introduces new arguments. Yet, full
controllability can be achieved in a strong sense: e.g., in a time dependent
Jaynes-Cummings model we show that, by tuning coupling constants appropriately,
every unitary of the coupled system (atoms and cavity) can be approximated with
arbitrarily small error
Structural influences in thermoelectric materials
Thermoelectric properties such as thermopower, electronic and thermal conductivity are governed by the underlying bonding interactions and local structural arrangements. This presentation will provide examples on how changing the local structural situation in materials affects thermoelectric transport directly. For instance, in the quaternary Cu2MGeQ4 (M = Zn, Fe; Q = S, Se), the local bonding situation on the one hand leads to moving valence and conduction bands as well as enhanced point defect scattering on the other hand. Further examples include materials such as Yb1-xZn2Sb2 and CoSb3. Understanding the underlying structure, defect chemistry, and temperature dependent structural changes helps to understand effects such as doping efficiencies and apparent band convergence
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