1,040 research outputs found
Role of Fermion Exchanges in Statistical Signatures of Composite Bosons
We study statistical signatures of composite bosons made of two fermions
using a new many-body approach. Extending number-states to composite bosons,
two-particle correlations as well as the dispersion of the probability
distribution are analyzed. We show that the particle composite nature reduces
the anti-bunching effect predicted for elementary bosons. Furthermore, the
probability distribution exhibits a dispersion which is greater for composite
bosons than for elementary bosons. This dispersion corresponds to the one of
sub-Poissonian processes, as for a quantum state, but, unlike its elementary
boson counterpart, it is not minimum. In general, our work shows that it is
necessary to take into account the Pauli exclusion principle which takes place
between fermionic components of composite bosons - along the line here used -
to possibly extract statistical properties in a precise way.Comment: 14 page
An electronic model for self-assembled hybrid organic/perovskite semiconductors: reverse band edge electronic states ordering and spin-orbit coupling
Based on density functional theory, the electronic and optical properties of
hybrid organic/perovskite crystals are thoroughly investigated. We consider the
mono-crystalline 4FPEPI as material model and demonstrate the optical process
is governed by three active Bloch states at the {\Gamma} point of the reduced
Brillouin zone with a reverse ordering compared to tetrahedrally bonded
semiconductors. Giant spin-orbit coupling effects and optical activities are
subsequently inferred from symmetry analysis.Comment: 17 pages, 6 figure
Non-orthogonal Theory of Polarons and Application to Pyramidal Quantum Dots
We present a general theory for semiconductor polarons in the framework of
the Froehlich interaction between electrons and phonons. The latter is
investigated using non-commuting phonon creation/annihilation operators
associated with a natural set of non-orthogonal modes. This setting proves
effective for mathematical simplification and physical interpretation and
reveals a nested coupling structure of the Froehlich interaction. The theory is
non-perturbative and well adapted for strong electron-phonon coupling, such as
found in quantum dot (QD) structures. For those particular structures we
introduce a minimal model that allows the computation and qualitative
prediction of the spectrum and geometry of polarons. The model uses a generic
non-orthogonal polaron basis, baptized the "natural basis". Accidental and
symmetry-related electronic degeneracies are studied in detail and are shown to
generate unentangled zero-shift polarons, which we consistently eliminate. As a
practical example, these developments are applied to realistic pyramidal GaAs
QDs. The energy spectrum and the 3D-geometry of polarons are computed and
analyzed, and prove that realistic pyramidal QDs clearly fall in the regime of
strong coupling. Further investigation reveals an unexpected substructure of
"weakly coupled strong coupling regimes", a concept originating from overlap
considerations. Using Bennett's entanglement measure, we finally propose a
heuristic quantification of the coupling strength in QDs.Comment: 17 pages, 11 figures, 3 table
Closure relations for composite bosons: difference between polaritons and Wannier or Frenkel excitons
We derive the closure relation for polaritons made of three different
types of excitons: bosonized excitons, Frenkel or Wannier excitons. In the case
of polaritons made of Wannier excitons, we show how this closure relation,
which appears as non-diagonal, may reduce to the one of elementary bosons,
the photons, with its prefactor, or to the one of Wannier excitons,
with its prefactor. Widely different forms of closure relations are
thus found depending on the composite bosons at hand. Comparison with closure
relations of excitons, either bosonized or kept composite as Frenkel or Wannier
excitons, allows us to discuss the influence of a reduction of the number of
internal degrees of freedom, as well as the importance of the composite nature
of the particles and the existence of fermionic components
Control of atomic decay rates via manipulation of reservoir mode frequencies
We analyse the problem of a two-level atom interacting with a time-dependent
dissipative environment modelled by a bath of reservoir modes. In the model of
this paper the principal features of the reservoir structure remain constant in
time, but the microscopic structure does not. In the context of an atom in a
leaky cavity this corresponds to a fixed cavity and a time-dependent external
bath. In this situation we show that by chirping the reservoir modes
sufficiently fast it is possible to inhibit, or dramatically enhance the decay
of the atomic system, even though the gross reservoir structure is fixed. Thus
it is possible to extract energy from a cavity-atom system faster than the
empty cavity rate. Similar, but less dramatic effects are possible for moderate
chirps where partial trapping of atomic population is also possible.Comment: 12 pages, 9 figure
Minimum decoherence cat-like states in Gaussian noisy channels
We address the evolution of cat-like states in general Gaussian noisy
channels, by considering superpositions of coherent and squeezed-coherent
states coupled to an arbitrarily squeezed bath. The phase space dynamics is
solved and decoherence is studied keeping track of the purity of the evolving
state. The influence of the choice of the state and channel parameters on
purity is discussed and optimal working regimes that minimize the decoherence
rate are determined. In particular, we show that squeezing the bath to protect
a non squeezed cat state against decoherence is equivalent to orthogonally
squeezing the initial cat state while letting the bath be phase insensitive.Comment: 10 pages, 2 figures, references added, submitted to J. Opt.
Enhancement of the Binding Energy of Charged Excitons in Disordered Quantum Wires
Negatively and positively charged excitons are identified in the
spatially-resolved photoluminescence spectra of quantum wires. We demonstrate
that charged excitons are weakly localized in disordered quantum wires. As a
consequence, the enhancement of the "binding energy" of a charged exciton is
caused, for a significant part, by the recoil energy transferred to the
remaining charged carrier during its radiative recombination. We discover that
the Coulomb correlation energy is not the sole origin of the "binding energy",
in contrast to charged excitons confined in quantum dots.Comment: 4 Fig
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