1,669 research outputs found
Simple Phase Bias for Superconducting Circuits
A phase-bias tool, based on a trapped fluxoid in a ring, is proposed and
demonstrated. It can provide arbitrary phase values and is simple to fabricate.
The phase bias has been realized in two superconducting quantum interference
devices, where the critical current versus magnetic flux is shown to be shifted
by a \pi/2 and \pi.Comment: 5 pages, including 4 figures. Submitted to AP
Tax Competition under Minimum Rates: The Case of European Diesel Excises
This paper estimates Nash-type fiscal reaction functions for European governments competing for revenue from diesel excises. It appears that European governments strategically set their excise levels by responding to their neighbors’ tax rates. This provides evidence for the presence of tax competition in diesel excises. In fact, a 10 percent higher rate in neighboring countries (in terms of the user price) induces a country to raise its own rate by between 2 and 3 percent. This impact is robust for alternative specifications. By imposing restrictions on excise levels, EU harmonization of excises in 1987 and the introduction of a minimum in 1992 exerted a positive impact on the excise level in a number of EU countries. It has not, however, significantly reduced the intensity of tax competition. Indeed, strategic tax responses have not significantly been reduced by these harmonization policies. We also find that high-tax countries appear to compete more aggressively than low-tax countries in the sense that they feature larger strategic tax responses. There is no significant difference between large and small countries.Diesel excise, strategic tax setting, minimum rates, European Union
The merger of vertically offset quasi-geostrophic vortices
We examine the critical merging distance between two equal-volume, equal-potential-vorticity quasi-geostrophic vortices. We focus on how this distance depends on the vertical offset between the two vortices, each having a unit mean height-to-width aspect ratio. The vertical direction is special in the quasi-geostrophic model (used to capture the leading-order dynamical features of stably stratified and rapidly rotating geophysical flows) since vertical advection is absent. Nevertheless vortex merger may still occur by horizontal advection. In this paper, we first investigate the equilibrium states for the two vortices as a function of their vertical and horizontal separation. We examine their basic properties together with their linear stability. These findings are next compared to numerical simulations of the nonlinear evolution of two spheres of potential vorticity. Three different regimes of interaction are identified, depending on the vertical offset. For a small offset, the interaction differs little from the case when the two vortices are horizontally aligned. On the other hand, when the vertical offset is comparable to the mean vortex radius, strong interaction occurs for greater horizontal gaps than in the horizontally aligned case, and therefore at significantly greater full separation distances. This perhaps surprising result is consistent with the linear stability analysis and appears to be a consequence of the anisotropy of the quasi-geostrophic equations. Finally, for large vertical offsets, vortex merger results in the formation of a metastable tilted dumbbell vortex.Publisher PDFPeer reviewe
QND measurement of a superconducting qubit in the weakly projective regime
Quantum state detectors based on switching of hysteretic Josephson junctions
biased close to their critical current are simple to use but have strong
back-action. We show that the back-action of a DC-switching detector can be
considerably reduced by limiting the switching voltage and using a fast
cryogenic amplifier, such that a single readout can be completed within 25 ns
at a repetition rate of 1 MHz without loss of contrast. Based on a sequence of
two successive readouts we show that the measurement has a clear quantum
non-demolition character, with a QND fidelity of 75 %.Comment: submitted to PR
The GROUSE project III: Ks-band observations of the thermal emission from WASP-33b
In recent years, day-side emission from about a dozen hot Jupiters has been
detected through ground-based secondary eclipse observations in the
near-infrared. These near-infrared observations are vital for determining the
energy budgets of hot Jupiters, since they probe the planet's spectral energy
distribution near its peak. The aim of this work is to measure the Ks-band
secondary eclipse depth of WASP-33b, the first planet discovered to transit an
A-type star. This planet receives the highest level of irradiation of all
transiting planets discovered to date. Furthermore, its host-star shows
pulsations and is classified as a low-amplitude delta-Scuti. As part of our
GROUnd-based Secondary Eclipse (GROUSE) project we have obtained observations
of two separate secondary eclipses of WASP-33b in the Ks-band using the LIRIS
instrument on the William Herschel Telescope (WHT). The telescope was
significantly defocused to avoid saturation of the detector for this bright
star (K~7.5). To increase the stability and the cadence of the observations,
they were performed in staring mode. We collected a total of 5100 and 6900
frames for the first and the second night respectively, both with an average
cadence of 3.3 seconds. On the second night the eclipse is detected at the
12-sigma level, with a measured eclipse depth of 0.244+0.027-0.020 %. This
eclipse depth corresponds to a brightness temperature of 3270+115-160 K. The
measured brightness temperature on the second night is consistent with the
expected equilibrium temperature for a planet with a very low albedo and a
rapid re-radiation of the absorbed stellar light. For the other night the short
out-of-eclipse baseline prevents good corrections for the stellar pulsations
and systematic effects, which makes this dataset unreliable for eclipse depth
measurements. This demonstrates the need of getting a sufficient out-of-eclipse
baseline.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Nondestructive readout for a superconducting flux qubit
We present a new readout method for a superconducting flux qubit, based on
the measurement of the Josephson inductance of a superconducting quantum
interference device that is inductively coupled to the qubit. The intrinsic
flux detection efficiency and back-action are suitable for a fast and
nondestructive determination of the quantum state of the qubit, as needed for
readout of multiple qubits in a quantum computer. We performed spectroscopy of
a flux qubit and we measured relaxation times of the order of 80 .Comment: 4 pages, 4 figures; modified content, figures and references;
accepted for publication in Phys. Rev. Let
Correlated electron states and transport in triangular arrays
We study correlated electron states in frustrated geometry of a triangular
lattice. The interplay of long range interactions and finite residual entropy
of a classical system gives rise to unusual effects in equilibrium ordering as
well as in transport. A novel correlated fluid phase is identified in a wide
range of densities and temperatures above freezing into commensurate solid
phases. The charge dynamics in the correlated phase is described in terms of a
height field, its fluctuations, and topological defects. We demonstrate that
the height field fluctuations give rise to a ``free'' charge flow and finite dc
conductivity. We show that freezing into the solid phase, controlled by the
long range interactions, manifests itself in singularities of transport
properties.Comment: 19 pages, 10 figure
Josephson squelch filter for quantum nanocircuits
We fabricated and tested a squelch circuit consisting of a copper powder
filter with an embedded Josephson junction connected to ground. For small
signals (squelch-ON), the small junction inductance attenuates strongly from DC
to at least 1 GHz, while for higher frequencies dissipation in the copper
powder increases the attenuation exponentially with frequency. For large
signals (squelch-OFF) the circuit behaves as a regular metal powder filter. The
measured ON/OFF ratio is larger than 50dB up to 50 MHz. This squelch can be
applied in low temperature measurement and control circuitry for quantum
nanostructures such as superconducting qubits and quantum dots.Comment: Corrected and completed references 6,7,8. Updated some minor details
in figure
- …