416 research outputs found
An electrostatically defined serial triple quantum dot charged with few electrons
A serial triple quantum dot (TQD) electrostatically defined in a GaAs/AlGaAs
heterostructure is characterized by using a nearby quantum point contact as
charge detector. Ground state stability diagrams demonstrate control in the
regime of few electrons charging the TQD. An electrostatic model is developed
to determine the ground state charge configurations of the TQD. Numerical
calculations are compared with experimental results. In addition, the tunneling
conductance through all three quantum dots in series is studied. Quantum
cellular automata processes are identified, which are where charge
reconfiguration between two dots occurs in response to the addition of an
electron in the third dot.Comment: 12 pages, 9 figure
Quantum interference and phonon-mediated back-action in lateral quantum dot circuits
Spin qubits have been successfully realized in electrostatically defined,
lateral few-electron quantum dot circuits. Qubit readout typically involves
spin to charge information conversion, followed by a charge measurement made
using a nearby biased quantum point contact. It is critical to understand the
back-action disturbances resulting from such a measurement approach. Previous
studies have indicated that quantum point contact detectors emit phonons which
are then absorbed by nearby qubits. We report here the observation of a
pronounced back-action effect in multiple dot circuits where the absorption of
detector-generated phonons is strongly modified by a quantum interference
effect, and show that the phenomenon is well described by a theory
incorporating both the quantum point contact and coherent phonon absorption.
Our combined experimental and theoretical results suggest strategies to
suppress back-action during the qubit readout procedure.Comment: 25 pages, 8 figure
Theory of electronic transport through a triple quantum dot in the presence of magnetic field
Theory of electronic transport through a triangular triple quantum dot
subject to a perpendicular magnetic field is developed using a tight binding
model. We show that magnetic field allows to engineer degeneracies in the
triple quantum dot energy spectrum. The degeneracies lead to zero electronic
transmission and sharp dips in the current whenever a pair of degenerate states
lies between the chemical potential of the two leads. These dips can occur with
a periodicity of one flux quantum if only two levels contribute to the current
or with half flux quantum if the three levels of the triple dot contribute. The
effect of strong bias voltage and different lead-to-dot connections on
Aharonov-Bohm oscillations in the conductance is also discussed
The origin of switching noise in GaAs/AlGaAs lateral gated devices
We have studied the origin of switching (telegraph) noise at low temperature
in lateral quantum structures defined electrostatically in GaAs/AlGaAs
heterostructures by surface gates. The noise was measured by monitoring the
conductance fluctuations around on the first step of a quantum point
contact at around 1.2 K. Cooling with a positive bias on the gates dramatically
reduces this noise, while an asymmetric bias exacerbates it. We propose a model
in which the noise originates from a leakage current of electrons that tunnel
through the Schottky barrier under the gate into the doped layer. The key to
reducing noise is to keep this barrier opaque under experimental conditions.
Bias cooling reduces the density of ionized donors, which builds in an
effective negative gate voltage. A smaller negative bias is therefore needed to
reach the desired operating point. This suppresses tunnelling from the gate and
hence the noise. The reduction in the density of ionized donors also
strengthens the barrier to tunneling at a given applied voltage. Support for
the model comes from our direct observation of the leakage current into a
closed quantum dot, around for this device. The current
was detected by a neighboring quantum point contact, which showed monotonic
steps in time associated with the tunneling of single electrons into the dot.
If asymmetric gate voltages are applied, our model suggests that the noise will
increase as a consequence of the more negative gate voltage applied to one of
the gates to maintain the same device conductance. We observe exactly this
behaviour in our experiments.Comment: 8 pages, 7 figure
Actual and ideal roles of school staff to support students with special needs: Current needs and strategies for improvement
To optimise school-based service delivery for students with disabilities, it is important to understand roles and needs of school staff. This study aimed to clarify ideal and actual roles of school staff (teachers, special educators, administrators) working with students with special needs, and to identify potential strategies to support actual roles. Ninety-five school personnel (64% teachers) from 3 different elementary schools and school boards in Quebec completed a 14-question survey. Open-ended responses were coded and analysed thematically. Common actual roles included task adaptation, offering individualized support, being available, and teamwork. Respondents felt roles could improve through in-context professional support, continuing education, teamwork opportunities extending to partnerships with families, and access to resources. Clarifying roles and expectations within a tiered-model to best support students also emerged, emphasizing the importance of sharing responsibilities across all service providers. Findings can guide implementation strategies and processes for providing effective services, enabling inclusion for students
Solid-state Marx based two-switch voltage modulator for the On-Line Isotope Mass Separator accelerator at the European Organization for Nuclear Research
A new circuit topology is proposed to replace the actual pulse transformer and thyratron based resonant modulator that supplies the 60 kV target potential for the ion acceleration of the On-Line Isotope Mass Separator accelerator, the stability of which is critical for the mass resolution downstream separator, at the European Organization for Nuclear Research. The improved modulator uses two solid-state switches working together, each one based on the Marx generator concept, operating as series and parallel switches, reducing the stress on the series stacked semiconductors, and also as auxiliary pulse generator in order to fulfill the target requirements. Preliminary results of a 10 kV prototype, using 1200 V insulated gate bipolar transistors and capacitors in the solid-state Marx circuits, ten stages each, with an electrical equivalent circuit of the target, are presented, demonstrating both the improved voltage stability and pulse flexibility potential wanted for this new modulator
Gene expression differentiation in the reproductive tissues of Drosophila willistoni subspecies and their hybrids
Ultrafast electronic read-out of diamond NV centers coupled to graphene
Nonradiative transfer processes are often regarded as loss channels for an
optical emitter1, since they are inherently difficult to be experimentally
accessed. Recently, it has been shown that emitters, such as fluorophores and
nitrogen vacancy centers in diamond, can exhibit a strong nonradiative energy
transfer to graphene. So far, the energy of the transferred electronic
excitations has been considered to be lost within the electron bath of the
graphene. Here, we demonstrate that the trans-ferred excitations can be
read-out by detecting corresponding currents with picosecond time resolution.
We electrically detect the spin of nitrogen vacancy centers in diamond
electronically and con-trol the nonradiative transfer to graphene by electron
spin resonance. Our results open the avenue for incorporating nitrogen vacancy
centers as spin qubits into ultrafast electronic circuits and for harvesting
non-radiative transfer processes electronically
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