Higher dimensional Calabi-Yau manifolds of Kummer type

Based on Cynk-Hulek method we construct complex Calabi-Yau varieties of arbitrary dimensions using elliptic curves with automorphism of order 6. Also we give formulas for Hodge numbers of varieties obtained from that construction. We shall generalize result of Katsura and Sch\"utt to obtain arbitrarily dimensional Calabi-Yau manifolds which are Zariski in any characteristic $p\not\equiv 1\pmod{12}.$Comment: 13 pages, 2 figure

Towards visualisation of central-cell-effects in scanning-tunnelling-microscope images of subsurface dopant qubits in silicon

Atomic-scale understanding of phosphorous donor wave functions underpins the design and optimisation of silicon based quantum devices. The accuracy of large-scale theoretical methods to compute donor wave functions is dependent on descriptions of central-cell-corrections, which are empirically fitted to match experimental binding energies, or other quantities associated with the global properties of the wave function. Direct approaches to understanding such effects in donor wave functions are of great interest. Here, we apply a comprehensive atomistic theoretical framework to compute scanning tunnelling microscopy (STM) images of subsurface donor wave functions with two central-cell-correction formalisms previously employed in the literature. The comparison between central-cell models based on real-space image features and the Fourier transform profiles indicate that the central-cell effects are visible in the simulated STM images up to ten monolayers below the silicon surface. Our study motivates a future experimental investigation of the central-cell effects via STM imaging technique with potential of fine tuning theoretical models, which could play a vital role in the design of donor-based quantum systems in scalable quantum computer architectures.Comment: Nanoscale 201

Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots

We investigate exciton spin memory in individual InAs/GaAs self-assembled quantum dots via optical alignment and conversion of exciton polarization in a magnetic field. Quasiresonant phonon-assisted excitation is successfully employed to define the initial spin polarization of neutral excitons. The conservation of the linear polarization generated along the bright exciton eigenaxes of up to 90% and the conversion from circular- to linear polarization of up to 47% both demonstrate a very long spin relaxation time with respect to the radiative lifetime. Results are quantitatively compared with a model of pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure

Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges

We propose an engineering of the optical properties of GaAs/AlGaAs quantum wells using AlAs and InAs monolayer insertions. A quantitative study of the effects of the monolayer position and the well thickness on the interband and intersubband transitions, based on the extended-basis sp3d5s* tight-binding model, is presented. The effect of insertion on the interband transitions is compared with existing experimental data. As for intersubband transitions, we show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs insertions, a three level {e1 , e2 , e3 } system where the transition energy e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal optical phonon energy (36 meV) can be engineered together with a e3-e2 transition energy widely tunable through the TeraHertz range

Seasonal variations of concentrations and optical properties of water soluble HULIS collected in urban environments

Major contributors to the organic aerosol include water-soluble macromolecular compounds (e.g. HULIS<sub>WS</sub>: Water Soluble Humic LIke Substances). The nature and sources of HULIS<sub>WS</sub> are still largely unknown. This work is based on a monitoring in six different French cities performed during summer and winter seasons. HULIS<sub>WS</sub> analysis was performed with a selective method of extraction complemented by carbon quantification. UV spectroscopy was also applied for their chemical characterisation. HULIS<sub>WS</sub> carbon represent an important contribution to the organic aerosol mass in summer and winter, as it accounts for 12–22% of Organic Carbon and 34–40% of Water Soluble Organic Carbon. We found strong differences in the optical properties (specific absorbance at 250, 272, 280 nm and E2/E3 ratio) and therefore in the chemical structure between HULIS<sub>WS</sub> from samples of summer- and wintertime. These differences highlight different processes responsible for emissions and formation of HULIS<sub>WS</sub> according to the season, namely biomass burning in winter, and secondary processes in summer. Specific absorbance can also be considered as a rapid and useful indicator of the origin of HULIS<sub>WS</sub> in urban environment

Optically probing the fine structure of a single Mn atom in an InAs quantum dot

We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD) doped with a single Mn atom in a longitudinal magnetic field of a few Tesla. Our findings show that the Mn impurity is a neutral acceptor state A^0 whose effective spin J=1 is significantly perturbed by the QD potential and its associated strain field. The spin interaction with photo-carriers injected in the quantum dot is shown to be ferromagnetic for holes, with an effective coupling constant of a few hundreds of micro-eV, but vanishingly small for electrons.Comment: 5 pages, 3 figure

Valley filtering and spatial maps of coupling between silicon donors and quantum dots

Exchange coupling is a key ingredient for spin-based quantum technologies since it can be used to entangle spin qubits and create logical spin qubits. However, the influence of the electronic valley degree of freedom in silicon on exchange interactions is presently the subject of important open questions. Here we investigate the influence of valleys on exchange in a coupled donor/quantum dot system, a basic building block of recently proposed schemes for robust quantum information processing. Using a scanning tunneling microscope tip to position the quantum dot with sub-nm precision, we find a near monotonic exchange characteristic where lattice-aperiodic modulations associated with valley degrees of freedom comprise less than 2~\% of exchange. From this we conclude that intravalley tunneling processes that preserve the donor's $\pm x$ and $\pm y$ valley index are filtered out of the interaction with the $\pm z$ valley quantum dot, and that the $\pm x$ and $\pm y$ intervalley processes where the electron valley index changes are weak. Complemented by tight-binding calculations of exchange versus donor depth, the demonstrated electrostatic tunability of donor/QD exchange can be used to compensate the remaining intravalley $\pm z$ oscillations to realise uniform interactions in an array of highly coherent donor spins.Comment: 6 pages, 4 figures, 6 pages Supplemental Materia