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

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

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

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.

Auger radiation targeted into DNA: a therapy perspective

BACKGROUND: Auger electron emitters that can be targeted into DNA of tumour cells represent an attractive systemic radiation therapy goal. In the situation of DNA-associated decay, the high linear energy transfer (LET) of Auger electrons gives a high relative biological efficacy similar to that of alpha particles. In contrast to alpha radiation, however, Auger radiation is of low toxicity when decaying outside the cell nucleus, as in cytoplasm or outside cells during blood transport. The challenge for such therapies is the requirement to target a high percentage of all cancer cells. An overview of Auger radiation therapy approaches of the past decade shows several research directions and various targeting vehicles. The latter include hormones, peptides, halogenated nucleotides, oligonucleotides and internalising antibodies. DISCUSSION: Here, we will discuss the basic principles of Auger electron therapy as compared with vector-guided alpha and beta radiation. We also review some radioprotection issues and briefly present the main advantages and disadvantages of the different targeting modalities that are under investigation

Entanglement and purity of two-mode Gaussian states in noisy channels

We study the evolution of purity, entanglement and total correlations of general two--mode Gaussian states of continuous variable systems in arbitrary uncorrelated Gaussian environments. The time evolution of purity, Von Neumann entropy, logarithmic negativity and mutual information is analyzed for a wide range of initial conditions. In general, we find that a local squeezing of the bath leads to a faster degradation of purity and entanglement, while it can help to preserve the mutual information between the modes.Comment: 10 pages, 8 figure

Short fluorodeoxyuridine exposure of different human glioblastoma lines induces high-level accumulation of S-phase cells that avidly incorporate 125I-iododeoxyuridine.

PURPOSE: Radio-iododeoxyuridine (IdUrd) is a potential Auger radiation therapy agent incorporated into DNA during the synthesis phase. In this study we sought to optimise S-phase targeting by modulating cellular cycling and radio-IdUrd DNA incorporation using short non-toxic fluorodeoxyuridine (FdUrd) incubations. METHODS: Three human glioblastoma cell lines with different p53 expression were pre-treated with various FdUrd conditions. After different intervals, (125)I-IdUrd DNA incorporation was measured. Fluorescence-activated cell sorter cell cycle analysis was performed after identical intervals post FdUrd pre-treatment. RESULTS: The highest increase in (125)I-IdUrd DNA incorporation was induced by 1-h incubation with 1 muM FdUrd. Increase in radio-IdUrd DNA incorporation was greatest 16-24 h after FdUrd, reaching factors of >or=7.5 over baseline incorporation in the three cell lines. Furthermore, cell synchronisation in S phase was observed with a peak of >or=69.5% in the three cell lines at 16 and 24 h post FdUrd, corresponding to an increase of 2.5-4.1 over baseline. CONCLUSION: FdUrd-induced thymidine synthesis inhibition led to S-phase accumulation that was maximal after an interval of 16-24 h and time-correlated with the highest radio-IdUrd DNA incorporation. These observations might allow the rational design of an Auger radiation therapy targeting a maximal number of S-phase cells in single treatment cycles

Maximal symetrization and reduction of fields: application to wavefunctions in solid state nanostructures

A novel general formalism for the maximal symetrization and reduction of fields (MSRF) is proposed and applied to wavefunctions in solid state nanostructures. Its primary target is to provide an essential tool for the study and analysis of the electronic and optical properties of semiconductor quantum heterostructures with relatively high point-group symmetry, and studied with the $k\cdot p$ formalism. Nevertheless the approach is valid in a much larger framework than $k\cdot p$ theory, it is applicable to arbitrary systems of coupled partial differential equations (e.g. strain equations or Maxwell equations). For spinless problems (scalar equations), one can use a systematic Spatial Domain Reduction (SDR) technique which allows, for every irreducible representation, to reduce the set of equations on a minimal domain with automatic incorporation of the boundary conditions at the border, which are shown to be non-trivial in general. For a vectorial or spinorial set of functions, the SDR technique must be completed by the use of an optimal basis in vectorial or spinorial space (in a crystal we call it the Optimal Bloch function Basis - OBB). The advantages are numerous: sharper insights on the symmetry properties of every eigenstate, minimal coupling schemes, analytically and computationally exploitable at the component function level, minimal computing domains. The formalism can be applied also as a postprocessing operation, offering all subsequent analytical and computationnal advantages of symmetrization. The specific case of a quantum wire (QWRs) with $C_{3v}$ point group symmetry is used as a concrete illustration of the application of MSRF.Comment: 33 pages, 13 figures, Many small changes in equations, which use more standard conventions in the passive point of view, and corrections of a number of minor mistake

Dependence of transient dynamics in a class-C laser upon variation of inversion with time

The transient statistics of a gain-switched coherently pumped class-C laser displays a linear correlation between the first passage time and subsequent peak intensity. Measurements are reported showing a positive or negative sign of this linear correlation, controlled through the switching time and the laser detuning. Further measurements of the small-signal laser gain combined with calculations involving a three-level laser model indicate that this sign fundamentally depends upon the way the laser inversion varies during the gain switching, despite the added dynamics of the laser polarization in the class-C laser. [S1050-2947(97)07112-6]

Quantifying decoherence in continuous variable systems

We present a detailed report on the decoherence of quantum states of continuous variable systems under the action of a quantum optical master equation resulting from the interaction with general Gaussian uncorrelated environments. The rate of decoherence is quantified by relating it to the decay rates of various, complementary measures of the quantum nature of a state, such as the purity, some nonclassicality indicators in phase space and, for two-mode states, entanglement measures and total correlations between the modes. Different sets of physically relevant initial configurations are considered, including one- and two-mode Gaussian states, number states, and coherent superpositions. Our analysis shows that, generally, the use of initially squeezed configurations does not help to preserve the coherence of Gaussian states, whereas it can be effective in protecting coherent superpositions of both number states and Gaussian wave packets.Comment: Review article; 36 pages, 19 figures; typos corrected, references adde