1,233 research outputs found
Entanglement of a qubit with a single oscillator mode
We solve a model of a qubit strongly coupled to a massive environmental
oscillator mode where the qubit backaction is treated exactly. Using a
Ginzburg-Landau formalism, we derive an effective action for this well known
localization transition. An entangled state emerges as an instanton in the
collective qubit-environment degree of freedom and the resulting model is shown
to be formally equivalent to a Fluctuating Gap Model (FGM) of a disordered
Peierls chain. Below the transition, spectral weight is transferred to an
exponentially small energy scale leaving the qubit coherent but damped. Unlike
the spin-boson model, coherent and effectively localized behaviors may coexist.Comment: 4 pages, 1 figure; added calculation of entanglement entrop
A more patient-friendly use of circular fixators in deformity correction
PURPOSE: The evaluation of a construction that allows the exchange of circular and unilateral external fixators on the same fixation pins to the bone in outpatient circumstances during bone lengthening and alignment procedures. METHODS: Nine children were treated with this concept. After bone lengthening and alignment, the circular fixators were exchanged for unilateral fixators in the outpatient clinic to hold the position of the bony parts during the consolidation phase. RESULTS: The decrease of time needed to use the circular fixator during the treatment was considered to be an improvement in comfort. CONCLUSIONS: The concept of using both a circular and a unilateral external fixator in a construction that allows the exchange of the external fixators in outpatient circumstances combines the advantages of both systems, and creates more options in the different stages of bone deformity correction. Patient comfort is increased by the decrease of time needed to use the circular fixator
Identification and tunable optical coherent control of transition-metal spins in silicon carbide
Color centers in wide-bandgap semiconductors are attractive systems for
quantum technologies since they can combine long-coherent electronic spin and
bright optical properties. Several suitable centers have been identified, most
famously the nitrogen-vacancy defect in diamond. However, integration in
communication technology is hindered by the fact that their optical transitions
lie outside telecom wavelength bands. Several transition-metal impurities in
silicon carbide do emit at and near telecom wavelengths, but knowledge about
their spin and optical properties is incomplete. We present all-optical
identification and coherent control of molybdenum-impurity spins in silicon
carbide with transitions at near-infrared wavelengths. Our results identify
spin for both the electronic ground and excited state, with highly
anisotropic spin properties that we apply for implementing optical control of
ground-state spin coherence. Our results show optical lifetimes of 60 ns
and inhomogeneous spin dephasing times of 0.3 s, establishing
relevance for quantum spin-photon interfacing.Comment: Updated version with minor correction, full Supplementary Information
include
No Apparent Costs for Facultative Antibiotic Production by the Soil Bacterium Pseudomonas fluorescens Pf0-1
Background: Many soil-inhabiting bacteria are known to produce secondary metabolites that can suppress microorganisms
competing for the same resources. The production of antimicrobial compounds is expected to incur fitness costs for the
producing bacteria. Such costs form the basis for models on the co-existence of antibiotic-producing and non-antibiotic
producing strains. However, so far studies quantifying the costs of antibiotic production by bacteria are scarce. The current
study reports on possible costs, for antibiotic production by Pseudomonas fluorescens Pf0-1, a soil bacterium that is induced
to produce a broad-spectrum antibiotic when it is confronted with non-related bacterial competitors or supernatants of
their cultures.
Methodology and Principal Findings: We measured the possible cost of antibiotic production for Pseudomonas fluorescens
Pf0-1 by monitoring changes in growth rate with and without induction of antibiotic production by supernatant of a
bacterial competitor, namely Pedobacter sp.. Experiments were performed in liquid as well as on semi-solid media under
nutrient-limited conditions that are expected to most clearly reveal fitness costs. Our results did not reveal any significant
costs for production of antibiotics by Pseudomonas fluorescens Pf0-1. Comparison of growth rates of the antibioticproducing
wild-type cells with those of non-antibiotic producing mutants did not reveal costs of antibiotic production
either.
Significance: Based on our findings we propose that the facultative production of antibiotics might not be selected to
mitigate metabolic costs, but instead might be advantageous because it limits the risk of competitors evolving resistance, or
even the risk of competitors feeding on the compounds produced.
Method for direct observation of coherent quantum oscillations in a superconducting phase qubit
Time-domain observations of coherent oscillations between quantum states in
mesoscopic superconducting systems were so far restricted to restoring the
time-dependent probability distribution from the readout statistics. We propose
a new method for direct observation of Rabi oscillations in a phase qubit. The
external source, typically in GHz range, induces transitions between the qubit
levels. The resulting Rabi oscillations of supercurrent in the qubit loop are
detected by a high quality resonant tank circuit, inductively coupled to the
phase qubit. Detailed calculation for zero and non-zero temperature are made
for the case of persistent current qubit. According to the estimates for
dephasing and relaxation times, the effect can be detected using conventional
rf circuitry, with Rabi frequency in MHz range.Comment: 5 pages, 1 figure, to appear in Phys.Rev.
Furnace for in situ and simultaneous studies of nano-precipitates and phase transformations in steels by SANS and neutron diffraction
Interphase precipitation occurring during solid-state phase transformations in micro-alloyed steels is generally studied through transmission electron microscopy, atom probe tomography, and ex situ measurements of Small-Angle Neutron Scattering (SANS). The advantage of SANS over the other two characterization techniques is that SANS allows for the quantitative determination of size distribution, volume fraction, and number density of a statistically significant number of precipitates within the resulting matrix at room temperature. However, the performance of ex situ SANS measurements alone does not provide information regarding the probable correlation between interphase precipitation and phase transformations. This limitation makes it necessary to perform in situ and simultaneous studies on precipitation and phase transformations in order to gain an in-depth understanding of the nucleation and growth of precipitates in relation to the evolution of austenite decomposition at high temperatures. A furnace is, thus, designed and developed for such in situ studies in which SANS measurements can be simultaneously performed with neutron diffraction measurements during the application of high-temperature thermal treatments. The furnace is capable of carrying out thermal treatments involving fast heating and cooling as well as high operation temperatures (up to 1200 °C) for a long period of time with accurate temperature control in a protective atmosphere and in a magnetic field of up to 1.5 T. The characteristics of this furnace give the possibility of developing new research studies for better insight of the relationship between phase transformations and precipitation kinetics in steels and also in other types of materials containing nano-scale microstructural features.This work was financially supported equally by the Technology Foundation TTW, as part of the Netherlands Organization for Scientific Research (NWO), and Tata Steel Europe through the Grant No. 14307 under the Project No. S41.5.14548 in the framework of the Materials Innovation Institute (M2i) Partnership Program. The experiments performed at ISIS Neutron and Muon Source were supported by beam-time allocation from the Netherlands Organization for Scientific Research (NWO) through Project No. 721.012.102 (LARMOR) with Experiment No. RB1869024
Fairness in Algorithmic Decision Making: An Excursion Through the Lens of Causality
As virtually all aspects of our lives are increasingly impacted by
algorithmic decision making systems, it is incumbent upon us as a society to
ensure such systems do not become instruments of unfair discrimination on the
basis of gender, race, ethnicity, religion, etc. We consider the problem of
determining whether the decisions made by such systems are discriminatory,
through the lens of causal models. We introduce two definitions of group
fairness grounded in causality: fair on average causal effect (FACE), and fair
on average causal effect on the treated (FACT). We use the Rubin-Neyman
potential outcomes framework for the analysis of cause-effect relationships to
robustly estimate FACE and FACT. We demonstrate the effectiveness of our
proposed approach on synthetic data. Our analyses of two real-world data sets,
the Adult income data set from the UCI repository (with gender as the protected
attribute), and the NYC Stop and Frisk data set (with race as the protected
attribute), show that the evidence of discrimination obtained by FACE and FACT,
or lack thereof, is often in agreement with the findings from other studies. We
further show that FACT, being somewhat more nuanced compared to FACE, can yield
findings of discrimination that differ from those obtained using FACE.Comment: 7 pages, 2 figures, 2 tables.To appear in Proceedings of the
International Conference on World Wide Web (WWW), 201
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