Hole spin dephasing time associated to hyperfine interaction in quantum dots

The spin interaction of a hole confined in a quantum dot with the surrounding nuclei is described in terms of an effective magnetic field. We show that, in contrast to the Fermi contact hyperfine interaction for conduction electrons, the dipole-dipole hyperfine interaction is anisotropic for a hole, for both pure or mixed hole states. We evaluate the coupling constants of the hole-nuclear interaction and demonstrate that they are only one order of magnitude smaller than the coupling constants of the electron-nuclear interaction. We also study, theoretically, the hole spin dephasing of an ensemble of quantum dots via the hyperfine interaction in the framework of frozen fluctuations of the nuclear field, in absence or in presence of an applied magnetic field. We also discuss experiments which could evidence the dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table

Quantum Mechanical Aspects of Cell Microtubules: Science Fiction or Realistic Possibility?

Recent experimental research with marine algae points towards quantum entanglement at ambient temperature, with correlations between essential biological units separated by distances as long as 20 Angstr\"oms. The associated decoherence times, due to environmental influences, are found to be of order 400 fs. This prompted some authors to connect such findings with the possibility of some kind of quantum computation taking place in these biological entities: within the decoherence time scales, the cell "quantum calculates" the optimal "path" along which energy and signal would be transported more efficiently. Prompted by these experimental results, in this talk I remind the audience of a related topic proposed several years ago in connection with the possible r\^ole of quantum mechanics and/or field theory on dissipation-free energy transfer in microtubules (MT), which constitute fundamental cell substructures. Quantum entanglement between tubulin dimers was argued to be possible, provided there exists sufficient isolation from other environmental cell effects. The model was based on certain ferroelectric aspects of MT. In the talk I review the model and the associated experimental tests so far and discuss future directions, especially in view of the algae photo-experiments.Comment: 31 pages latex, 11 pdf figures, uses special macros, Invited Plenary Talk at DICE2010, Castello Pasquini, Castiglioncello (Italy), September 13-18 201

Dark States and Interferences in Cascade Transitions of Ultra-Cold Atoms in a Cavity

We examine the competition among one- and two-photon processes in an ultra-cold, three-level atom undergoing cascade transitions as a result of its interaction with a bimodal cavity. We show parameter domains where two-photon transitions are dominant and also study the effect of two-photon emission on the mazer action in the cavity. The two-photon emission leads to the loss of detailed balance and therefore we obtain the photon statistics of the cavity field by the numerical integration of the master equation. The photon distribution in each cavity mode exhibits sub- and super- Poissonian behaviors depending on the strength of atom-field coupling. The photon distribution becomes identical to a Poisson distribution when the atom-field coupling strengths of the modes are equal.Comment: 15 pages including 7 figures in Revtex, submitted to PR

Transient Linear Dichroism in InAs/GaAs Self-Assembled Quantum Dots

International audienceWe have shown that a transient linear dichroism can be photo-induced in self-assembled InAs/GaAs QDs along the [110] and [110] crystallographic axes. The transient signal shows characteristic times of 42 ps and 1.1 ns at 1.35 eV. We have also performed time-resolved photoluminescence studies which lead to a lifetime between 700 ps and 1.4 ns, depending on the emission energy. By comparison of these results, we conclude that the spin relaxation time is seven times longer than the lifetime

Linear and dynamical photoinduced dichroisms of InAs/GaAs self-assembled quantum dots: Population relaxation and decoherence measurements

International audienceWe present and model our pump-probe experiments measuring the photoinduced dynamics of an ensemble of self-assembled InAs/GaAs quantum dots. A pulsed pump beam, linearly polarized along an in-plane symmetry axis of the quantum dots, photoinduces a linear dichroism. We show that the dynamics of this linear dichroism is consistent with a long spin relaxation time and allows us to measure different radiative lifetimes for both nondegenerate, low-lying, electron-hole pair states. In another experimental configuration, when the pump beam creates a coherent superposition of these electron-hole pair states, it photoinduces a dynamical dichroism, which gives information about quantum decoherence and provides the electron-hole anisotropic exchange interaction energy splitting, 41 +/- 8 mu eV at 1.343 eV. A model is developed, which accounts for the dynamical dichroism and predicts the experimental observations with good accuracy

Bright-exciton splittings in inorganic cesium lead halide perovskite nanocrystals

International audienceSince their first synthesis in 2015, the all-inorganic lead halide perovskite nanocrystals CsPbX3(X=Cl,Br,I) have attracted a great deal of attention due to their outstanding electronic and optical properties as well as their performances, which outclass the ones of their II–VI conterparts in many application fields. In addition to these properties, the understanding of the emission features in these systems at the single object scale is crucial, e.g., for nanophotonics and quantum optics devices. Here, the details of the band-edge excitonic emission are theoretically explored. The contribution of the long-range exchange interaction to the bright-exciton splittings is computed in strong and weak confinement regimes using group theory arguments and k⋅p approximation. We show that the shape anisotropy with the real crystalline (cubic, tetragonal, or orthorhombic) structures of nanocrystals explain well their emission properties. In the weak confinement regime, splittings are inversely proportional to the cube of the exciton Bohr radius and we observe an increase of the splittings from iodide, to bromide, and then to chloride perovskite compounds. However, in the strong confinement regime, splittings increase inversely proportional to the nanocrystal volume and, for a given nanocrystal size, the splitting values are comparable for the three-halide-perovskite materials. The present theoretical developments lead to quantitative contributions in good agreement with available experimental data mainly in the weak confinement regime

Nothing to lose: The power of subtle forms of Resistance in an Immigration detention centre

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