Quantum state detection of a superconducting flux qubit using a DC-SQUID in the inductive mode

We present a readout method for superconducting flux qubits. The qubit quantum flux state can be measured by determining the Josephson inductance of an inductively coupled DC superconducting quantum interference device (DC-SQUID). We determine the response function of the DC-SQUID and its back-action on the qubit during measurement. Due to driving, the qubit energy relaxation rate depends on the spectral density of the measurement circuit noise at sum and difference frequencies of the qubit Larmor frequency and SQUID driving frequency. The qubit dephasing rate is proportional to the spectral density of circuit noise at the SQUID driving frequency. These features of the backaction are qualitatively different from the case when the SQUID is used in the usual switching mode. For a particular type of readout circuit with feasible parameters we find that single shot readout of a superconducting flux qubit is possible.Comment: 11 pages, 3 figures; submitted to Phys. Rev.

Characterising exo-ringsystems around fast-rotating stars using the Rossiter-McLaughlin effect

Planetary rings produce a distinct shape distortion in transit lightcurves. However, to accurately model such lightcurves the observations need to cover the entire transit, especially ingress and egress, as well as an out-of-transit baseline. Such observations can be challenging for long period planets, where the transits may last for over a day. Planetary rings will also impact the shape of absorption lines in the stellar spectrum, as the planet and rings cover different parts of the rotating star (the Rossiter-McLaughlin effect). These line-profile distortions depend on the size, structure, opacity, obliquity and sky projected angle of the ring system. For slow rotating stars, this mainly impacts the amplitude of the induced velocity shift, however, for fast rotating stars the large velocity gradient across the star allows the line distortion to be resolved, enabling direct determination of the ring parameters. We demonstrate that by modeling these distortions we can recover ring system parameters (sky-projected angle, obliquity and size) using only a small part of the transit. Substructure in the rings, e.g. gaps, can be recovered if the width of the features ($\delta W$) relative to the size of the star is similar to the intrinsic velocity resolution (set by the width of the local stellar profile, $\gamma$) relative to the stellar rotation velocity ($v$ sin$i$, i.e. $\delta W / R_* \gtrsim v$sin$i$/$\gamma$). This opens up a new way to study the ring systems around planets with long orbital periods, where observations of the full transit, covering the ingress and egress, are not always feasible.Comment: Accepted for publication in MNRA

Tax Reform and the Dutch Labor Market: An Applied General Equilibrium Approach

This paper employs MIMIC, an applied general equilibrium model of the Dutch economy, to explore various tax cuts aimed at combating unemployment and raising labor supply. MIMIC combines modern labor-market theories, a firm empirical foundation detailed description of Dutch labor-market institutions. We develop a small aggregate model which contains the core of MIMIC, namely wage setting, job matching, labor supply demand. In addition to illustrating the main economic mechanisms in MIMIC shows the advantages of employing a larger, more disaggregated model that accounts for heterogeneity, institutional details, and more economic mechanisms. Targeting in-work benefits at the low skilled is the most effective way to cut economy-wide unemployment quality and quantity of labor supply. Cuts in social security contributions paid by employers and subsidies for hiring long-term unemployed reduce unskilled unemployment most substantially. Tax cuts in the higher tax brackets boost the quantity and quality of formal labor supply but are less effective in reducing unemployment and in raising unskilled employment and female labor supply.

Superconductor-insulator transition in nanowires and nanowire arrays

Superconducting nanowires are the dual elements to Josephson junctions, with quantum phase-slip processes replacing the tunneling of Cooper pairs. When the quantum phase-slip amplitude ES is much smaller than the inductive energy EL, the nanowire responds as a superconducting inductor. When the inductive energy is small, the response is capacitive. The crossover at low temperatures as a function of ES/EL is discussed and compared with earlier experimental results. For one-dimensional and two-dimensional arrays of nanowires quantum phase transitions are expected as a function of ES/EL. They can be tuned by a homogeneous magnetic frustration.Comment: 15 pages, 10 figure

A Weaker Faithfulness Assumption based on Triple Interactions

One of the core assumptions in causal discovery is the faithfulness assumption---i.e. assuming that independencies found in the data are due to separations in the true causal graph. This assumption can, however, be violated in many ways, including xor connections, deterministic functions or cancelling paths. In this work, we propose a weaker assumption that we call 2-adjacency faithfulness. In contrast to adjacency faithfulness, which assumes that there is no conditional independence between each pair of variables that are connected in the causal graph, we only require no conditional independence between a node and a subset of its Markov blanket that can contain up to two nodes. Equivalently, we adapt orientation faithfulness to this setting. We further propose a sound orientation rule for causal discovery that applies under weaker assumptions. As a proof of concept, we derive a modified Grow and Shrink algorithm that recovers the Markov blanket of a target node and prove its correctness under strictly weaker assumptions than the standard faithfulness assumption

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

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 $\mu s$.Comment: 4 pages, 4 figures; modified content, figures and references; accepted for publication in Phys. Rev. Let

The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b

For extrasolar planets discovered using the radial velocity method, the spectral characterization of the host star leads to a mass-estimate of the star and subsequently of the orbiting planet. In contrast, if also the orbital velocity of the planet would be known, the masses of both star and planet could be determined directly using Newton's law of gravity, just as in the case of stellar double-line eclipsing binaries. Here we report on the detection of the orbital velocity of extrasolar planet HD209458b. High dispersion ground-based spectroscopy during a transit of this planet reveals absorption lines from carbon monoxide produced in the planet atmosphere, which shift significantly in wavelength due to the change in the radial component of the planet orbital velocity. These observations result in a mass determination of the star and planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec blueshift of the carbon monoxide signal with respect to the systemic velocity of the host star suggests the presence of a strong wind flowing from the irradiated dayside to the non-irradiated nightside of the planet within the 0.01-0.1 mbar atmospheric pressure range probed by these observations. The strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3 in this planet's upper atmosphere.Comment: 11 Pages main article and 6 pages suppl. information: A final, edited version appears in the 24 May 2010 issue of Natur

What Explains the Variation in Estimates of Labour Supply Elasticities?

This paper performs a meta-analysis of empirical estimates of uncompensated labour supply elasticities. We find that much of the variation in elasticities can be explained by the variation in gender, participation rates, and country fixed effects. Country differences appear to be small though. There is no systematic impact of the model specification or marital status on reported elasticities. The decision to participate is more responsive than is the decision regarding hours worked. Even at the intensive margin, we find that the elasticity for women exceeds that for men. For men and women in the Netherlands, we predict an uncompensated labour supply elasticity of 0.1 and 0.5, respectively. These values are robust for alternative samples and specifications of the meta regression.labour supply, meta-analysis, uncompensated elasticity