144 research outputs found
Understanding the saturation power of Josephson Parametric Amplifiers made from SQUIDs arrays
We report on the implementation and detailed modelling of a Josephson
Parametric Amplifier (JPA) made from an array of eighty Superconducting QUantum
Interference Devices (SQUIDs), forming a non-linear quarter-wave resonator.
This device was fabricated using a very simple single step fabrication process.
It shows a large bandwidth (45 MHz), an operating frequency tunable between 5.9
GHz and 6.8 GHz and a large input saturation power (-117 dBm) when biased to
obtain 20 dB of gain. Despite the length of the SQUID array being comparable to
the wavelength, we present a model based on an effective non-linear LC series
resonator that quantitatively describes these figures of merit without fitting
parameters. Our work illustrates the advantage of using array-based JPA since a
single-SQUID device showing the same bandwidth and resonant frequency would
display a saturation power 15 dB lower.Comment: 12 pages, 9 figures, Appendices include
Kerr non-linearity in a superconducting Josephson metamaterial
We present a detailed experimental and theoretical analysis of the dispersion
and non-linear Kerr frequency shifts of plasma modes in a one-dimensional
Josephson junction chain containing 500 SQUIDs in the regime of weak
nonlinearity. The measured low-power dispersion curve agrees perfectly with the
theoretical model if we take into account the Kerr renormalisation of the bare
frequencies and the long-range nature of the island charge screening by a
remote ground plane. We measured the self- and cross-Kerr shifts for the
frequencies of the eight lowest modes in the chain. We compare the measured
Kerr coefficients with theory and find good agreement
A way to measure electron spin-flipping at F/N interfaces and application to Co/Cu
We describe a technique, using the current-perpendicular-to-plane (CPP)
geometry, to measure the parameter delta(F/N), characterizing flipping of
electron spins at a ferromagnetic/non-magnetic (F/N) metallic interface. The
technique involves measuring the CPP magnetoresistance of a sample containing a
ferromagnetically coupled [F/N]x n multilayer embedded within the 20 nm thick
central Cu layer of a symmetric Py-based, double exchange-biased spin-valve. To
focus on delta(F/N), the F- and N-layers are made thin compared to their
spin-diffusion lengths. We test the technique using F/N = Co/Cu. Analysing with
no adjustable parameters, gives inconsistency with delta(Co/Cu) = 0, but
consistency with our prior value of delta(Co/Cu) = 0.25 (+/- 0.1). Taking
delta(Co/Cu) as adjustable gives delta(Co/Cu) = 0.33 (+0.03/-0.08).Comment: 3 pages, 2 figures. To appear in Applied Physics Letter
Fast high fidelity quantum non-demolition qubit readout via a non-perturbative cross-Kerr coupling
Qubit readout is an indispensable element of any quantum information
processor. In this work, we experimentally demonstrate a non-perturbative
cross-Kerr coupling between a transmon and a polariton mode which enables an
improved quantum non-demolition (QND) readout for superconducting qubits. The
new mechanism uses the same experimental techniques as the standard QND qubit
readout in the dispersive approximation, but due to its non-perturbative
nature, it maximizes the speed, the single-shot fidelity and the QND properties
of the readout. In addition, it minimizes the effect of unwanted decay channels
such as the Purcell effect. We observed a single-shot readout fidelity of 97.4%
for short 50 ns pulses, and we quantified a QND-ness of 99% for long
measurement pulses with repeated single-shot readouts
Use of partial least squares regression to impute SNP genotypes in Italian Cattle breeds
Background
The objective of the present study was to test the ability of the partial least squares regression technique to impute genotypes from low density single nucleotide polymorphisms (SNP) panels i.e. 3K or 7K to a high density panel with 50K SNP. No pedigree information was used.
Methods
Data consisted of 2093 Holstein, 749 Brown Swiss and 479 Simmental bulls genotyped with the Illumina 50K Beadchip. First, a single-breed approach was applied by using only data from Holstein animals. Then, to enlarge the training population, data from the three breeds were combined and a multi-breed analysis was performed. Accuracies of genotypes imputed using the partial least squares regression method were compared with those obtained by using the Beagle software. The impact of genotype imputation on breeding value prediction was evaluated for milk yield, fat content and protein content.
Results
In the single-breed approach, the accuracy of imputation using partial least squares regression was around 90 and 94% for the 3K and 7K platforms, respectively; corresponding accuracies obtained with Beagle were around 85% and 90%. Moreover, computing time required by the partial least squares regression method was on average around 10 times lower than computing time required by Beagle. Using the partial least squares regression method in the multi-breed resulted in lower imputation accuracies than using single-breed data. The impact of the SNP-genotype imputation on the accuracy of direct genomic breeding values was small. The correlation between estimates of genetic merit obtained by using imputed versus actual genotypes was around 0.96 for the 7K chip.
Conclusions
Results of the present work suggested that the partial least squares regression imputation method could be useful to impute SNP genotypes when pedigree information is not available
Qubit readout using in-situ bifurcation of a nonlinear dissipative polariton in the mesoscopic regime
We explore the nonlinear response to a strong drive of polaritonic meters for
superconducting qubit state readout. The two polaritonic meters result from the
strong hybridization between a bosonic mode of a 3D microwave cavity and an
anharmonic ancilla mode of the superconducting circuit. Both polaritons inherit
a self-Kerr nonlinearity , and decay rate from the ancilla and
cavity, respectively. They are coupled to a transmon qubit via a
non-perturbative cross-Kerr coupling resulting in a large cavity pull . By applying magnitic flux, the ancilla mode frequency varies
modifying the hybridization conditions and thus the properties of the readout
polariton modes. Using this, the hybridisation is tuned in the mesoscopic
regime of the non-linear dissipative polariton where the self-Kerr and decay
rates of one polariton are similar leading to bistability and
bifurcation behavior at small photon number. This bistability and bifurcation
behavior depends on the qubit state and we report qubit state readout in a
latching-like manner thanks to the bifurcation of the upper polariton. Without
any external quantum-limited amplifier, we obtain a single-shot fidelity of
in a ns integration time
Design of a Bovine Low-Density SNP Array Optimized for Imputation
The Illumina BovineLD BeadChip was designed to support imputation to higher density genotypes in dairy and beef breeds by including single-nucleotide polymorphisms (SNPs) that had a high minor allele frequency as well as uniform spacing across the genome except at the ends of the chromosome where densities were increased. The chip also includes SNPs on the Y chromosome and mitochondrial DNA loci that are useful for determining subspecies classification and certain paternal and maternal breed lineages. The total number of SNPs was 6,909. Accuracy of imputation to Illumina BovineSNP50 genotypes using the BovineLD chip was over 97% for most dairy and beef populations. The BovineLD imputations were about 3 percentage points more accurate than those from the Illumina GoldenGate Bovine3K BeadChip across multiple populations. The improvement was greatest when neither parent was genotyped. The minor allele frequencies were similar across taurine beef and dairy breeds as was the proportion of SNPs that were polymorphic. The new BovineLD chip should facilitate low-cost genomic selection in taurine beef and dairy cattle
Propagating Quantum Microwaves: Towards Applications in Communication and Sensing
The field of propagating quantum microwaves has started to receive
considerable attention in the past few years. Motivated at first by the lack of
an efficient microwave-to-optical platform that could solve the issue of secure
communication between remote superconducting chips, current efforts are
starting to reach other areas, from quantum communications to sensing. Here, we
attempt at giving a state-of-the-art view of the two, pointing at some of the
technical and theoretical challenges we need to address, and while providing
some novel ideas and directions for future research. Hence, the goal of this
paper is to provide a bigger picture, and -- we hope -- to inspire new ideas in
quantum communications and sensing: from open-air microwave quantum key
distribution to direct detection of dark matter, we expect that the recent
efforts and results in quantum microwaves will soon attract a wider audience,
not only in the academic community, but also in an industrial environment
The Hierarchical Age-Period-Cohort model: Why does it find the results that it finds?
It is claimed the hierarchical-age–period–cohort (HAPC) model solves the age–period–cohort (APC) identification problem. However, this is debateable; simulations show situations where the model produces incorrect results, countered by proponents of the model arguing those simulations are not relevant to real-life scenarios. This paper moves beyond questioning whether the HAPC model works, to why it produces the results it does. We argue HAPC estimates are the result not of the distinctive substantive APC processes occurring in the dataset, but are primarily an artefact of the data structure—that is, the way the data has been collected. Were the data collected differently, the results produced would be different. This is illustrated both with simulations and real data, the latter by taking a variety of samples from the National Health Interview Survey (NHIS) data used by Reither et al. (Soc Sci Med 69(10):1439–1448, 2009) in their HAPC study of obesity. When a sample based on a small range of cohorts is taken, such that the period range is much greater than the cohort range, the results produced are very different to those produced when cohort groups span a much wider range than periods, as is structurally the case with repeated cross-sectional data. The paper also addresses the latest defence of the HAPC model by its proponents (Reither et al. in Soc Sci Med 145:125–128, 2015a). The results lend further support to the view that the HAPC model is not able to accurately discern APC effects, and should be used with caution when there appear to be period or cohort near-linear trends
Electoral Volatility, Political Sophistication, Trust and Efficacy
In this article we investigate voter volatility and analyze the causes and motives of switching vote intentions. We test two main sets of variables linked to volatility in literature; political sophistication and ‘political (dis)satisfaction’. Results show that voters with low levels of political efficacy tend to switch more often, both within a campaign and between elections. In the analysis we differentiate between campaign volatility and inter-election volatility and by doing so show that the dynamics of a campaign have a profound impact on volatility. The campaign period is when the lowly sophisticated switch their vote intention. Those with higher levels of interest in politics have switched their intention before the campaign has started. The data for this analysis are from the three wave PartiRep Belgian Election Study (2009)
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