79 research outputs found
Charge Offset Stability in Si Single Electron Devices with Al Gates
We report on the charge offset drift (time stability) in Si single electron
devices (SEDs) defined with aluminum (Al) gates. The size of the charge offset
drift (0.15 ) is intermediate between that of Al/AlO/Al tunnel junctions
(greater than 1 ) and Si SEDs defined with Si gates (0.01 ). This range
of values suggests that defects in the AlO are the main cause of the charge
offset drift instability
Overlapping-gate architecture for silicon Hall bar MOSFET devices in the low electron density regime
We report the fabrication and study of Hall bar MOSFET devices in which an
overlapping-gate architecture allows four-terminal measurements of low-density
2D electron systems, while maintaining a high density at the ohmic contacts.
Comparison with devices made using a standard single gate show that
measurements can be performed at much lower densities and higher channel
resistances, despite a reduced peak mobility. We also observe a voltage
threshold shift which we attribute to negative oxide charge, injected during
electron-beam lithography processing.Comment: 4 pages, 4 figures, submitted for Applied Physics Letter
Accessing the Full Capabilities of Filter Functions: A Tool for Detailed Noise and Control Susceptibility Analysis
The filter function formalism from quantum control theory is typically used
to determine the noise susceptibility of pulse sequences by looking at the
overlap between the filter function of the sequence and the noise power
spectral density. Importantly, the square modulus of the filter function is
used for this method, hence directional and phase information is lost. In this
work, we take advantage of the full filter function including directional and
phase information. By decomposing the filter function with phase preservation
before taking the modulus, we are able to consider the contributions to -,
- and -rotation separately. Continuously driven systems provide noise
protection in the form of dynamical decoupling by cancelling low-frequency
noise, however, generating control pulses synchronously with an arbitrary
driving field is not trivial. Using the decomposed filter function we look at
the controllability of a system under arbitrary driving fields, as well as the
noise susceptibility, and also relate the filter function to the geometric
formalism
Gate-based spin readout of hole quantum dots with site-dependent factors
The rapid progress of hole spin qubits in group IV semiconductors has been
driven by their potential for scalability. This is owed to the compatibility
with industrial manufacturing standards, as well as the ease of operation and
addressability via all-electric drives. However, owing to a strong spin-orbit
interaction, these systems present variability and anisotropy in key qubit
control parameters such as the Land\'e factor, requiring careful
characterisation for reliable qubit operation. Here, we experimentally
investigate a hole double quantum dot in silicon by carrying out spin readout
with gate-based reflectometry. We show that characteristic features in the
reflected phase signal arising from magneto-spectroscopy convey information on
site-dependent factors in the two dots. Using analytical modeling, we
extract the physical parameters of our system and, through numerical
calculations, we extend the results to point out the prospect of conveniently
extracting information about the local factors from reflectometry
measurements.Comment: Main manuscript: 12 pages, 8 figures. Supplementary Information: 3
pages, 2 figure
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