12,191 research outputs found
Anisotropic Stark Effect and Electric-Field Noise Suppression for Phosphorus Donor Qubits in Silicon
We report the use of novel, capacitively terminated coplanar waveguide (CPW)
resonators to measure the quadratic Stark shift of phosphorus donor qubits in
Si. We confirm that valley repopulation leads to an anisotropic spin-orbit
Stark shift depending on electric and magnetic field orientations relative to
the Si crystal. By measuring the linear Stark effect, we estimate the effective
electric field due to strain in our samples. We show that in the presence of
this strain, electric-field sources of decoherence can be non-negligible. Using
our measured values for the Stark shift, we predict magnetic fields for which
the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing
decoherence from electric-field noise. We discuss the limitations of these
noise-suppression points due to random distributions of strain and propose a
method for overcoming them
Simultaneous use of LANDSAT digital data with that of geophysical and geological surveys in geomathematical modelling for mineral exploration prediction
The author has identified the following significant results. A computer test file was created for the analysis of two rows in the pilot area. Data were organized into two groups with and without radioactivity above 1200 counts. The first 42 samples corresponded to the geographic cells which were anomalous, and the rest of the samples (70) were without anomalous values. Output analysis shows that all samples were properly classified
Electron Spin Resonance at the Level of 10000 Spins Using Low Impedance Superconducting Resonators
We report on electron spin resonance (ESR) measurements of phosphorus donors
localized in a 200 square micron area below the inductive wire of a lumped
element superconducting resonator. By combining quantum limited parametric
amplification with a low impedance microwave resonator design we are able to
detect around 20000 spins with a signal-to-noise ratio (SNR) of 1 in a single
shot. The 150 Hz coupling strength between the resonator field and individual
spins is significantly larger than the 1 - 10 Hz coupling rates obtained with
typical coplanar waveguide resonator designs. Due to the larger coupling rate,
we find that spin relaxation is dominated by radiative decay into the resonator
and dependent upon the spin-resonator detuning, as predicted by Purcell
Reevaluation of the normative minerals of Sonora Pass rock standards - University of Nevada reports 7 and 12
Chemical analyses and normative minerals of Nevada mountain pass rock
Some anomalies in the E-layer of the ionosphere
If in the course of our investigation some
problems have been clarified it is evident from the
foregoing discussion that many characteristics of
the E -layer remain mysterious, either having several
equally plausible explanations or none at all; and
there is no dearth of theoretical problems awaiting
solution. Let us however summarize briefly the
salient features of the present position.On the theoretical side we can now, with the
aid of the formulae developed in Chapter 2, readily
compute values of the maximum electron density Nᵐ
throughout the day for any assigned variation of
electron production q with solar zenith distance X,
assuming a recombination law of electron loss. As a result, particularly with the extension of the
calculation to the non -stationary conditions near
sunrise and sunset, we may be certain that neither
the anomalous variation of Δ fE nor the high exponent
of cos X can be put down to inaccuracies of the
theory. Hence we have been led to seek their origin
elsewhere.Undoubtedly the main step forward in this respect
has been the identification of the pre-noon perturbations in Nᵐ and in the height of the layer as effects
of the vertical drift of neutral ionization associated
with the Sq current system. This not only accounts
for several previously unexplained anomalies, including
increased values of fE near the equator, but is also
perhaps of somewhat broader scientific interest; for
it provides independent evidence of the existence and
the location of these ionospheric currents previously
only inferred from the data of the magnetic variations
at the ground.This identification was first made on the basis
of a statistical investigation of routine data; but
the special measurements made at Slough have provided
useful confirmation and have shown that the predicted
dip in hᵐ does in fact occur. Our theoretical
investigations of drift have also contributed by
clarifying the nature of the drift effects and by
enabling us to calculate the magnitudes of the drift
velocity and of its gradient.As to the high exponent of cos X fit, the September
results have suggested as a possible explanation that
stratification of the layer in the morning and evening
may lead to incorrect readings of fE. It seems that
if at such times the upper discontinuity is taken to
indicate fE instead of the lower one selected in normal
practice, then the anomalous variation with cos X would
disappear. A decision on this question must however
await further evidence.Finally we have the low values of ΔfE at low
cos X( leading to an apparent rapid increase of
recombination coefficient with height; but so far
no satisfactory explanation of this anomaly has been
forthcoming, and there is only the somewhat nebulous
suggestion that it may be related to the curious
"ledging" phenomena which develop in the afternoon
period.Ledging may also be responsible for other
unexplained features such as the unexpected pre-noon
dip in yᵐ, and the anomalo!is variation of h'E in the
September data. Indeed it is hardly possible to study
a large number of E-region records without becoming
convinced that stratification, including all the
phenomena variously described as "Eˢ ", is a major
problem for future investigation. It may be that,
following clarification of the Sq effects, little
progress will be made in understanding other
peculiarities of the region until the problem of
these various subsidiary layers, or "ledges", has been
solved
Addressing spin transitions on 209Bi donors in silicon using circularly-polarized microwaves
Over the past decade donor spin qubits in isotopically enriched Si
have been intensely studied due to their exceptionally long coherence times.
More recently bismuth donor electron spins have become popular because Bi has a
large nuclear spin which gives rise to clock transitions (first-order
insensitive to magnetic field noise). At every clock transition there are two
nearly degenerate transitions between four distinct states which can be used as
a pair of qubits. Here it is experimentally demonstrated that these transitions
are excited by microwaves of opposite helicity such that they can be
selectively driven by varying microwave polarization. This work uses a
combination of a superconducting coplanar waveguide (CPW) microresonator and a
dielectric resonator to flexibly generate arbitrary elliptical polarizations
while retaining the high sensitivity of the CPW
Developments in electromagnetic tomography instrumentation.
A new EMT sensor and instrumentation is described which combines the best features of previous systems and has a modular structure to allow for future system expansion and development
Geological and geothermal investigations for HCMM-derived data
An attempt was made to match HCMM- and U2HCMR-derived temperature data over two test sites of very local size to similar data collected in the field at nearly the same times. Results indicate that HCMM investigations using resolutions cells of 500 m or so are best conducted with areally-extensive sites, rather than point observations. The excellent quality day-VIS imagery is particularly useful for lineament studies, as is the DELTA-T imagery. Attempts to register the ground observed temperatures (even for 0.5 sq mile targets) were unsuccessful due to excessive pixel-to-pixel noise on the HCMM data. Several computer models were explored and related to thermal parameter value changes with observed data. Unless quite complex models, with many parameters which can be observed (perhaps not even measured (perhaps not even measured) only under remote sensing conditions (e.g., roughness, wind shear, etc) are used, the model outputs do not match the observed data. Empirical relationship may be most readily studied
Computer program to predict noise of general aviation aircraft: User's guide
Program NOISE predicts General Aviation Aircraft far-field noise levels at FAA FAR Part 36 certification conditions. It will also predict near-field and cabin noise levels for turboprop aircraft and static engine component far-field noise levels
Coherence of Spin Qubits in Silicon
Given the effectiveness of semiconductor devices for classical computation
one is naturally led to consider semiconductor systems for solid state quantum
information processing. Semiconductors are particularly suitable where local
control of electric fields and charge transport are required. Conventional
semiconductor electronics is built upon these capabilities and has demonstrated
scaling to large complicated arrays of interconnected devices. However, the
requirements for a quantum computer are very different from those for classical
computation, and it is not immediately obvious how best to build one in a
semiconductor. One possible approach is to use spins as qubits: of nuclei, of
electrons, or both in combination. Long qubit coherence times are a
prerequisite for quantum computing, and in this paper we will discuss
measurements of spin coherence in silicon. The results are encouraging - both
electrons bound to donors and the donor nuclei exhibit low decoherence under
the right circumstances. Doped silicon thus appears to pass the first test on
the road to a quantum computer.Comment: Submitted to J Cond Matter on Nov 15th, 200
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