630 research outputs found
Efficient orthogonal control of tunnel couplings in a quantum dot array
Electrostatically-defined semiconductor quantum dot arrays offer a promising
platform for quantum computation and quantum simulation. However, crosstalk of
gate voltages to dot potentials and inter-dot tunnel couplings complicates the
tuning of the device parameters. To date, crosstalk to the dot potentials is
routinely and efficiently compensated using so-called virtual gates, which are
specific linear combinations of physical gate voltages. However, due to
exponential dependence of tunnel couplings on gate voltages, crosstalk to the
tunnel barriers is currently compensated through a slow iterative process. In
this work, we show that the crosstalk on tunnel barriers can be efficiently
characterized and compensated for, using the fact that the same exponential
dependence applies to all gates. We demonstrate efficient calibration of
crosstalk in a quadruple quantum dot array and define a set of virtual barrier
gates, with which we show orthogonal control of all inter-dot tunnel couplings.
Our method marks a key step forward in the scalability of the tuning process of
large-scale quantum dot arrays.Comment: 8 pages, 7 figure
The Influence of Contrast and Temporal Expansion on the Marching-on-in-Time Contrast Current Density Volume Integral Equation
The contrast current density volume integral equation, discretized with
piecewise constant spatial basis and test functions and Dirac-delta temporal
test functions and the piecewise polynomial temporal basis functions, results
in a causal implicit marching-on-in-time scheme that we refer to as the
marching-on-in-time contrast current density volume integral equation
(MOT-JVIE). The companion matrix stability analysis of the MOT-JVIE solver
shows that for a fixed spatial and temporal step size, the stability is
independent of the scatterer's dielectric contrast for quadratic spline
temporal basis functions. Whereas, Lagrange and cubic spline exhibit
instabilities at higher contrast. We relate this stability performance to the
expansion and testing procedure in time. We further illustrate the capabilities
of the MOT-JVIE based on quadratic spline temporal basis functions by:
comparing the MOT-JVIE solution to time-domain results from literature and
frequency-domain results from a commercial combined field integral equation
solver. Finally, we present a long time sequence for a high-constrast scatterer
discretized with 24,000 spatial unknowns.Comment: 15 pages, 33 figures, correction of the labeling in Figure 3,
published in PIER
Automated tuning of inter-dot tunnel couplings in quantum dot arrays
Semiconductor quantum dot arrays defined electrostatically in a 2D electron
gas provide a scalable platform for quantum information processing and quantum
simulations. For the operation of quantum dot arrays, appropriate voltages need
to be applied to the gate electrodes that define the quantum dot potential
landscape. Tuning the gate voltages has proven to be a time-consuming task,
because of initial electrostatic disorder and capacitive cross-talk effects.
Here, we report on the automated tuning of the inter-dot tunnel coupling in a
linear array of gate-defined semiconductor quantum dots. The automation of the
tuning of the inter-dot tunnel coupling is the next step forward in scalable
and efficient control of larger quantum dot arrays. This work greatly reduces
the effort of tuning semiconductor quantum dots for quantum information
processing and quantum simulation
Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array
Interacting fermions on a lattice can develop strong quantum correlations,
which lie at the heart of the classical intractability of many exotic phases of
matter. Seminal efforts are underway in the control of artificial quantum
systems, that can be made to emulate the underlying Fermi-Hubbard models.
Electrostatically confined conduction band electrons define interacting quantum
coherent spin and charge degrees of freedom that allow all-electrical
pure-state initialisation and readily adhere to an engineerable Fermi-Hubbard
Hamiltonian. Until now, however, the substantial electrostatic disorder
inherent to solid state has made attempts at emulating Fermi-Hubbard physics on
solid-state platforms few and far between. Here, we show that for gate-defined
quantum dots, this disorder can be suppressed in a controlled manner. Novel
insights and a newly developed semi-automated and scalable toolbox allow us to
homogeneously and independently dial in the electron filling and
nearest-neighbour tunnel coupling. Bringing these ideas and tools to fruition,
we realize the first detailed characterization of the collective Coulomb
blockade transition, which is the finite-size analogue of the
interaction-driven Mott metal-to-insulator transition. As automation and device
fabrication of semiconductor quantum dots continue to improve, the ideas
presented here show how quantum dots can be used to investigate the physics of
ever more complex many-body states
Influence of sensitization and allergen provocation procedures on the development of allergen-induced bronchial hyperreactivity in conscious, unrestrained guinea-pigs
The effects of different sensitization and allergen provocation regimens on the development of allergen-induced bronchial hyperreactivity (BHR) to histamine were investigated in conscious, unrestrained guinea-pigs. Similar early and late phase asthmatic reactions, BHR for inhaled histamine after the early (6 h) as well as after the late reaction (24 h), and airway inflammation were observed after a single allergen provocation in animals sensitized to produce mainly IgG or IgE antibodies, respectively. Repeating the allergen provocation in the IgE-sensitized animals after 7 days, using identical provocation conditions, resulted in a similar development of BHR to histamine inhalation. Repetition of the allergen provocation during 4 subsequent days resulted in a decreased development of BHR after each provocation, despite a significant increase in the allergen provocation dose necessary to obtain similar airway obstruction. The number of inflammatory cells in the bronchoalveolar lavage was not significantly changed after repeated provocation, when compared with a single allergen provocation. Finally, we investigated allergen-induced bronchial hyperreactivity by repetition of the sensitization procedure at day 7 and 14 (booster), followed by repeated allergen provocation twice a week for 5 weeks. Surprisingly, no BHR to histamine could be observed after either provocation, while the number of inflammatory cells in the bronchoalveolar lavage fluid after 5 weeks was enhanced compared with controls. These data indicate that both IgE and IgG sensitized guinea-pigs may develop bronchial hyperreactivity after a single allergen provocation. Repeated allergen exposure of IgE sensitized animals causes a gradual fading of the induced hyperreactivity despite the on-going presence of inflammatory cells in the airways, indicating a mechanism of reduced cellular activation
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