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 $N$ 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 $N$ elementary bosons, the photons, with its $1/N!$ prefactor, or to the one of $N$ Wannier excitons, with its $(1/N!)^2$ 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