24,246 research outputs found
Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator
We present measurements on microwave spectroscopy on a double quantum dot
with an on-chip microwave source. The quantum dots are realized in the
two-dimensional electron gas of an AlGaAs/GaAs heterostructure and are weakly
coupled in series by a tunnelling barrier forming an 'ionic' molecular state.
We employ a Josephson oscillator formed by a long Nb/Al-AlO/Nb junction as
a microwave source. We find photon-assisted tunnelling sidebands induced by the
Josephson oscillator, and compare the results with those obtained using an
externally operated microwave source.Comment: 6 pages, 4 figure
Spin blockade in ground state resonance of a quantum dot
We present measurements on spin blockade in a laterally integrated quantum
dot. The dot is tuned into the regime of strong Coulomb blockade, confining ~
50 electrons. At certain electronic states we find an additional mechanism
suppressing electron transport. This we identify as spin blockade at zero bias,
possibly accompanied by a change in orbital momentum in subsequent dot ground
states. We support this by probing the bias, magnetic field and temperature
dependence of the transport spectrum. Weak violation of the blockade is
modelled by detailed calculations of non-linear transport taking into account
forbidden transitions.Comment: 4 pages, 4 figure
The finite-temperature thermodynamics of a trapped unitary Fermi gas within fractional exclusion statistics
We utilize a fractional exclusion statistics of Haldane and Wu hypothesis to
study the thermodynamics of a unitary Fermi gas trapped in a harmonic
oscillator potential at ultra-low finite temperature. The entropy per particle
as a function of the energy per particle and energy per particle versus
rescaled temperature are numerically compared with the experimental data. The
study shows that, except the chemical potential behavior, there exists a
reasonable consistency between the experimental measurement and theoretical
attempt for the entropy and energy per particle. In the fractional exclusion
statistics formalism, the behavior of the isochore heat capacity for a trapped
unitary Fermi gas is also analyzed.Comment: 6 pages, 6 figure
Recent increase in aerosol loading over the Australian arid zone
Collocated sun photometer and nephelometer measurements at Tinga Tingana in the Australian Outback over the decade 1997–2007 show a significant increase in aerosol loading following the onset of severe drought conditions in 2002. This increase is confined to the season of dust activity, particularly September to March. In contrast, background aerosol levels during May, June and July remained stable. The enhanced aerosol loadings during the latter 5 years of the study period can be understood as a combination of dune destabilisation through loss of ephemeral vegetation and surface crust, and the changing supply of fluvial sediments to ephemeral lakes and floodplains within the Lake Eyre Basin. Major dust outbreaks are generally highly localised, although significant dust activity was observed at Tinga Tingana on 50% of days when a major event occurred elsewhere in the Lake Eyre Basin, suggesting frequent basin-wide dust mobilisation. Combined analysis of aerosol optical depth and scattering coefficient shows weak correlation between the surface and column aerosol (<i>R</i><sup>2</sup>=0.24). The aerosol scale height is broadly distributed with a mode typically between 2–3 km, with clearly defined seasonal variation. Climatological analysis reveals bimodal structure in the annual cycle of aerosol optical depth, with a summer peak related to maximal dust activity, and a spring peak related to lofted fine-mode aerosol. There is evidence for an increase in near-surface aerosol during the period 2003–2007 relative to 1997–2002, consistent with an increase in dust activity. This accords with an independent finding of increasing aerosol loading over the Australian region as a whole, suggesting that rising dust activity over the Lake Eyre Basin may be a significant contributor to changes in the aerosol budget of the continent
Analysis of measurement errors for a superconducting phase qubit
We analyze several mechanisms leading to errors in a course of measurement of
a superconducting flux-biased phase qubit. Insufficiently long measurement
pulse may lead to nonadiabatic transitions between qubit states and
, before tunneling through a reduced barrier is supposed to distinguish
the qubit states. Finite (though large) ratio of tunneling rates for these
states leads to incomplete discrimination between and .
Insufficiently fast energy relaxation after the tunneling of state may
cause the repopulation of the quantum well in which only the state is
supposed to remain. We analyze these types of measurement errors using
analytical approaches as well as numerical solution of the time-dependent
Schr\"{o}dinger equation.Comment: 14 pages, 14 figure
Finite size spectrum, magnon interactions and magnetization of S=1 Heisenberg spin chains
We report our density matrix renormalization-group and analytical work on S=1
antiferromagnetic Heisenberg spin chains. We study the finite size behavior
within the framework of the non-linear sigma model. We study the effect of
magnon-magnon interactions on the finite size spectrum and on the magnetization
curve close to the critical magnetic field, determine the magnon scattering
length and compare it to the prediction from the non-linear model.Comment: 28 pages, 8 figures, made substantial improvement
Isocaling and the Symmetry Energy in the Multifragmentation Regime of Heavy Ion Collisions
The ratio of the symmetry energy coefficient to temperature, , in
Fermi energy heavy ion collisions, has been experimentally extracted as a
function of the fragment atomic number using isoscaling parameters and the
variance of the isotope distributions. The extracted values have been compared
to the results of calculations made with an Antisymmetrized Molecular Dynamics
(AMD) model employing a statistical decay code to account for deexcitation of
excited primary fragments. The experimental values are in good agreement with
the values calculated but are significantly different from those characterizing
the yields of the primary AMD fragments.Comment: 12 pages, 6 figure
On the sample size dependence of the critical current density in MgB superconductors
Sample size dependent critical current density has been observed in magnesium
diboride superconductors. At high fields, larger samples provide higher
critical current densities, while at low fields, larger samples give rise to
lower critical current densities. The explanation for this surprising result is
proposed in this study based on the electric field generated in the
superconductors. The dependence of the current density on the sample size has
been derived as a power law ( is the factor
characterizing curve ). This dependence provides one with
a new method to derive the factor and can also be used to determine the
dependence of the activation energy on the current density.Comment: Revtex, 4 pages, 5 figure
A 3,500-year tree-ring record of annual precipitation on the northeastern Tibetan Plateau
An annually resolved and absolutely dated ring-width chronology spanning 4,500 y has been constructed using subfossil, archaeological, and living-tree juniper samples from the northeastern Tibetan Plateau. The chronology represents changing mean annual precipitation and is most reliable after 1500 B.C. Reconstructed precipitation for this period displays a trend toward more moist conditions: the last 10-, 25-, and 50-y periods all appear to be the wettest in at least three and a half millennia. Notable historical dry periods occurred in the 4th century BCE and in the second half of the 15th century CE. The driest individual year reconstructed (since 1500 B.C.) is 1048 B.C., whereas the wettest is 2010. Precipitation variability in this region appears not to be associated with inferred changes in Asian monsoon intensity during recent millennia. The chronology displays a statistical association with the multidecadal and longer-term variability of reconstructed mean Northern Hemisphere temperatures over the last two millennia. This suggests that any further large-scale warming might be associated with even greater moisture supply in this region
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