174 research outputs found
Pressure of the Standard Model Near the Electroweak Phase Transition
We extend our previous determination of the thermodynamic pressure of the
Standard Model so that the result can be applied down to temperatures
corresponding to the electroweak crossover. This requires a further resummation
which can be cleanly organised within the effective theory framework. The
result allows for a precise determination of the expansion rate of the Universe
for temperatures around the electroweak crossover.Comment: 16 pages, 6 figures. v2: published versio
Pressure of the Standard Model at High Temperatures
We compute the pressure of the standard model at high temperatures in the
symmetric phase to three loops, or to O(g^5) in all coupling constants. We find
that the terms of the perturbative expansion in the SU(2) + Higgs sector
decrease monotonically with increasing order, but the large values of the
strong coupling constant g_s and the Yukawa coupling of the top quark g_Y make
the expansion in the full theory converge more slowly. The final result is
observed to be about 10% smaller than the ideal gas pressure commonly used in
cosmological calculations.Comment: 30 pages, 4 figures. v2: one reference added, minor revisions,
accepted for publication in JHE
Mesonic screening masses at high temperature and finite density
We compute the first perturbative correction to the static correlation
lengths of light quark bilinears in hot QCD with finite quark chemical
potentials. The correction is small and positive, with mu-dependence depending
on the relative sign of chemical potentials and the number of dynamical
flavors. The computation is carried out using a three-dimensional effective
theory for the lowest fermionic Matsubara mode. We also compute the full
correlator in free theory and find a rather complicated general mu-dependence
at shorter distances. Finally, rough comparisons with lattice simulations are
discussed.Comment: 24 pages, 5 figures, JHEP style. Minor corrections and
clarifications, version to appear in JHE
The ultraviolet limit and sum rule for the shear correlator in hot Yang-Mills theory
We determine a next-to-leading order result for the correlator of the shear
stress operator in high-temperature Yang-Mills theory. The computation is
performed via an ultraviolet expansion, valid in the limit of small distances
or large momenta, and the result is used for writing operator product
expansions for the Euclidean momentum and coordinate space correlators as well
as for the Minkowskian spectral density. In addition, our results enable us to
confirm and refine a shear sum rule originally derived by Romatschke, Son and
Meyer.Comment: 16 pages, 2 figures. v2: small clarifications, one reference added,
published versio
Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory
Inspired by recent lattice measurements, we determine the short-distance (a
> omega >> pi T) asymptotics
of scalar (trace anomaly) and pseudoscalar (topological charge density)
correlators at 2-loop order in hot Yang-Mills theory. The results are expressed
in the form of an Operator Product Expansion. We confirm and refine the
determination of a number of Wilson coefficients; however some discrepancies
with recent literature are detected as well, and employing the correct values
might help, on the qualitative level, to understand some of the features
observed in the lattice measurements. On the other hand, the Wilson
coefficients show slow convergence and it appears uncertain whether this
approach can lead to quantitative comparisons with lattice data. Nevertheless,
as we outline, our general results might serve as theoretical starting points
for a number of perhaps phenomenologically more successful lines of
investigation.Comment: 27 pages. v2: minor improvements, published versio
Microwave Package Design for Superconducting Quantum Processors
Solid-state qubits with transition frequencies in the microwave regime, such
as superconducting qubits, are at the forefront of quantum information
processing. However, high-fidelity, simultaneous control of superconducting
qubits at even a moderate scale remains a challenge, partly due to the
complexities of packaging these devices. Here, we present an approach to
microwave package design focusing on material choices, signal line engineering,
and spurious mode suppression. We describe design guidelines validated using
simulations and measurements used to develop a 24-port microwave package.
Analyzing the qubit environment reveals no spurious modes up to 11GHz. The
material and geometric design choices enable the package to support qubits with
lifetimes exceeding 350 {\mu}s. The microwave package design guidelines
presented here address many issues relevant for near-term quantum processors.Comment: 15 pages, 9 figure
Association of screen time with long-term stress and temperament in preschoolers: results from the DAGIS study
Screen time is increasing rapidly in young children. The aim of this
study was to examine associations of long-term stress and temperament
with screen time in Finnish preschool children and the moderating role
of socioeconomic status. Cross-sectional DAGIS data were utilized.
Long-term stress was assessed using hair cortisol concentration,
indicating values of the past 2Â months. Temperament was reported by the
parents using the Childrenâs Behavior Questionnaire (the Very Short
Form), and three broad temperament dimensions were constructed:
surgency, negative affectivity, and effortful control. Screen time was
reported by the parents over 7Â days. The highest education level in the
household was used as an indicator of socioeconomic status. In total,
779 children (mean age, 4.7â±â0.9 years, 52% boys) were included in the
study. Of the temperament dimensions, a higher effortful control was
associated with less screen time (BÂ =âââ6.70, pâ=â0.002).
There was no evidence for an association between hair cortisol
concentration and screen time nor a moderating role of socioeconomic
status in the associations (pâ>â0.05).Conclusion:
Our findings indicate that preschool children with a higher score in
effortful control had less screen time. Because effortful control
reflects general self-regulatory abilities, promoting these skills may
be effective in reducing screen time in young children.</p
Impact of ionizing radiation on superconducting qubit coherence
The practical viability of any qubit technology stands on long coherence
times and high-fidelity operations, with the superconducting qubit modality
being a leading example. However, superconducting qubit coherence is impacted
by broken Cooper pairs, referred to as quasiparticles, with a density that is
empirically observed to be orders of magnitude greater than the value predicted
for thermal equilibrium by the Bardeen-Cooper-Schrieffer (BCS) theory of
superconductivity. Previous work has shown that infrared photons significantly
increase the quasiparticle density, yet even in the best isolated systems, it
still remains higher than expected, suggesting that another generation
mechanism exists. In this Letter, we provide evidence that ionizing radiation
from environmental radioactive materials and cosmic rays contributes to this
observed difference, leading to an elevated quasiparticle density that would
ultimately limit superconducting qubits of the type measured here to coherence
times in the millisecond regime. We further demonstrate that introducing
radiation shielding reduces the flux of ionizing radiation and positively
correlates with increased coherence time. Albeit a small effect for today's
qubits, reducing or otherwise mitigating the impact of ionizing radiation will
be critical for realizing fault-tolerant superconducting quantum computers.Comment: 16 pages, 12 figure
Deep Neural Network Discrimination of Multiplexed Superconducting Qubit States
Demonstrating a quantum computational advantage will require high-fidelity
control and readout of multi-qubit systems. As system size increases,
multiplexed qubit readout becomes a practical necessity to limit the growth of
resource overhead. Many contemporary qubit-state discriminators presume
single-qubit operating conditions or require considerable computational effort,
limiting their potential extensibility. Here, we present multi-qubit readout
using neural networks as state discriminators. We compare our approach to
contemporary methods employed on a quantum device with five superconducting
qubits and frequency-multiplexed readout. We find that fully-connected
feedforward neural networks increase the qubit-state-assignment fidelity for
our system. Relative to contemporary discriminators, the assignment error rate
is reduced by up to 25% due to the compensation of system-dependent
nonidealities such as readout crosstalk which is reduced by up to one order of
magnitude. Our work demonstrates a potentially extensible building block for
high-fidelity readout relevant to both near-term devices and future
fault-tolerant systems.Comment: 18 Pages, 9 figure
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