Lower bound for electron spin entanglement from beamsplitter current correlations

We determine a lower bound for the entanglement of pairs of electron spins injected into a mesoscopic conductor. The bound can be expressed in terms of experimentally accessible quantities, the zero-frequency current correlators (shot noise power or cross-correlators) after transmission through an electronic beam splitter. The effect of spin relaxation (T_1 processes) and decoherence (T_2 processes) during the ballistic coherent transmission of the carriers in the wires is taken into account within Bloch theory. The presence of a variable inhomogeneous magnetic field allows the determination of a useful lower bound for the entanglement of arbitrary entangled states. The decrease in entanglement due to thermally mixed states is studied. Both the entanglement of the output of a source (entangler) and the relaxation (T_1) and decoherence (T_2) times can be determined.Comment: 4 pages, 3 figure

Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules

We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior which is strongly influenced by the tuning electric field and inter-molecular Coulomb energies. A rate equation model is developed to gain more insight into the charge transfer and tunneling mechanisms. Non-resonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.Comment: 4 pages, 4 figure

A comparison of microtensile and microcompression methods for studying plastic properties of nanocrystalline electrodeposited nickel at different length scales

A comparison of microcompression and microtensile methods to study mechanical properties of electrodeposited nanocrystalline (nc) nickel has been performed. Microtensile tests that probe a volume of more than 2 × 106 μm3 show reasonable agreement with results from microcompression tests that probe much smaller volumes down to a few μm3. Differences between the two uniaxial techniques are discussed in terms of measurements errors, probed volume and surface effects, strain rate, and influence of stress state. Uniaxial solicitation in compression mode revealed several advantages for studying stress-strain propertie

A comparison of microtensile and microcompression methods for studying plastic properties of nanocrystalline electrodeposited nickel at different length scales

A comparison of microcompression and microtensile methods to study mechanical properties of electrodeposited nanocrystalline (nc) nickel has been performed. Microtensile tests that probe a volume of more than 2 × 106 μm3 show reasonable agreement with results from microcompression tests that probe much smaller volumes down to a few μm3. Differences between the two uniaxial techniques are discussed in terms of measurements errors, probed volume and surface effects, strain rate, and influence of stress state. Uniaxial solicitation in compression mode revealed several advantages for studying stress–strain properties

Transition in plastic deformation of nanolayered thin films: Role of interfaces and temperature

Insights into the parameters governing the plasticity of immiscible, nanocrystalline metals stacked in the form of layers are pivotal both from scientific and applications’ perspectives. An outstanding case consists of the contact metallurgy of pure copper used ubiquitously as metallic interconnects in electronic devices. Diffusion barrier layers such W or TiN are necessary to prevent undesirable diffusion of Cu into the Si-based device during synthesis and service. Also, supersaturated Cu-Cr alloys are desirable for improving the strength, while retaining optimal functional properties required for the application. The scientific curiosity lies in understanding the effects of reducing microstructural length scales on the mechanical properties of both of these materials at elevated temperatures. In addition, alternate layering with an immiscible element forms a viable solution to the difficultly in synthesis and application of pure nanocrystalline materials due to their poor microstructural stability. The mechanical behavior of several nanolayered thin films consisting of soft and relatively hard metals or brittle ceramics have been extensively studied at ambient conditions [1-3] by using various models predicting strength as function of grain size or layer thickness. But, few have investigated the elevated temperature mechanical response [4] of similar systems and have been restricted to a specific metal (Al) – ceramic (SiC) combination [5]. This presentation attempts to highlight the role of interfaces and diffusion in plastic flow and failure of mutually immiscible, nanolayered systems at elevated temperatures. The nanolayered thin films consist of mainly sub-100 nm thick layers of pure Cu sandwiched by layers of pure metals of Cr and W and a pure ceramic of TiN, which were grown on Si(100) substrates to thickness of 2-5 μm by using direct current magnetron sputtering. The mechanical response at elevated temperatures of the films was studied by compressing micropillars, which were fabricated using a focused Ga+ beam, in situ SEM using an AlemnisÒ indenter modified for high temperature testing. Lateral flow of Cu promoted by stress-assisted diffusion at homologous temperatures as low as 0.35 occurred in all three systems in contrast to interfacial shear-dominated flow at lower temperatures (Fig. 1). Predictions of discrete dislocation and continuum plasticity models were used to evaluate the change in the yield strengths of the films with respect to the layer thicknesses of Cu in the different systems

Polarization fine-structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar micro-cavity

Single lateral InGaAs quantum dot molecules have been embedded in a planar micro-cavity in order to increase the luminescence extraction efficiency. Using a combination of metal-organic vapor phase and molecular beam epitaxy samples could be produced that exhibit a 30 times enhanced single-photon emission rate. We also show that the single-photon emission is fully switchable between two different molecular excitonic recombination energies by applying a lateral electric field. Furthermore, the presence of a polarization fine-structure splitting of the molecular neutral excitonic states is reported which leads to two polarization-split classically correlated biexciton exciton cascades. The fine-structure splitting is found to be on the order of 10 micro-eV.Comment: 14 pages, 4 figures; the following article has been submitted to Journal of Applied Physics (29th ICPS - invited paper); after it is published, it will be found at http://jap.aip.org

Phonon-Assisted Incoherent Excitation of a Quantum Dot and its Emission Properties

We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally-detuned laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20 % with respect to strictly resonant excitation can be achieved at T = 9 K. Laser frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the photoluminescence is introduced which predicts a broadband incoherent coupling process when electron-phonon scattering is in the strong phonon coupling (polaronic) regime. Additionally, we investigate the coherence properties of the emitted light and study the impact of the relevant pump and phonon bath parameters