3,569 research outputs found
Self-Excitation and Feedback Cooling of an Isolated Proton
The first one-proton self-excited oscillator (SEO) and one-proton feedback
cooling are demonstrated. In a Penning trap with a large magnetic gradient, the
SEO frequency is resolved to the high precision needed to detect a one-proton
spin flip. This is after undamped magnetron motion is sideband-cooled to a 14
mK theoretical limit, and despite random frequency shifts (larger than those
from a spin flip) that take place every time sideband cooling is applied in the
gradient. The observations open a possible path towards a million-fold improved
comparison of the antiproton and proton magnetic moments
Cavity Control of a Single-Electron Quantum Cyclotron:\\Measuring the Electron Magnetic Moment
Measurements with a one-electron quantum cyclotron determine the electron
magnetic moment, given by , and the fine structure
constant, . Brief
announcements of these measurements are supplemented here with a more complete
description of the one-electron quantum cyclotron and the new measurement
methods, a discussion of the cavity control of the radiation field, a summary
of the analysis of the measurements, and a fuller discussion of the
uncertainties
Past electron-positron g-2 experiments yielded sharpest bound on CPT violation for point particles
In our past experiments on a single electron and positron we measured the
cyclotron and spin-cyclotron difference frequencies omega_c and omega_a and the
ratios a = omega_a/ omega_c at omega_c = 141 Ghz for e^- and e^+ and later,
only for e^-, also at 164 Ghz. Here, we do extract from these data, as had not
done before, a new and very different figure of merit for violation of CPT
symmetry, one similar to the widely recognized impressive limit |m_Kaon -
m_Antikaon|/m_Kaon < 10^-18 for the K-mesons composed of two quarks. That
expression may be seen as comparing experimental relativistic masses of
particle states before and after the C, P, T operations had transformed
particle into antiparticle. Such a similar figure of merit for a non-composite
and quite different lepton, found by us from our Delta a = a^- - a^+ data, was
even smaller, h_bar |omega_a^- - omega_a^+|/2m_0 c^2 = |Delta a| h_bar
omega_c/2m_0 c^2) < 3(12) 10^-22.Comment: Improved content, Editorially approved for publication in PRL, LATEX
file, 5 pages, no figures, 16
Quantum Logic with a Single Trapped Electron
We propose the use of a trapped electron to implement quantum logic
operations. The fundamental controlled-NOT gate is shown to be feasible. The
two quantum bits are stored in the internal and external (motional) degrees of
freedom.Comment: 7 Pages, REVTeX, No Figures, To appear in Phys. Rev.
Direct high-precision measurement of the magnetic moment of the proton
The spin-magnetic moment of the proton is a fundamental property of
this particle. So far has only been measured indirectly, analysing the
spectrum of an atomic hydrogen maser in a magnetic field. Here, we report the
direct high-precision measurement of the magnetic moment of a single proton
using the double Penning-trap technique. We drive proton-spin quantum jumps by
a magnetic radio-frequency field in a Penning trap with a homogeneous magnetic
field. The induced spin-transitions are detected in a second trap with a strong
superimposed magnetic inhomogeneity. This enables the measurement of the
spin-flip probability as a function of the drive frequency. In each measurement
the proton's cyclotron frequency is used to determine the magnetic field of the
trap. From the normalized resonance curve, we extract the particle's magnetic
moment in units of the nuclear magneton . This
measurement outperforms previous Penning trap measurements in terms of
precision by a factor of about 760. It improves the precision of the forty year
old indirect measurement, in which significant theoretical bound state
corrections were required to obtain , by a factor of 3. By application
of this method to the antiproton magnetic moment the fractional
precision of the recently reported value can be improved by a factor of at
least 1000. Combined with the present result, this will provide a stringent
test of matter/antimatter symmetry with baryons.Comment: published in Natur
Possible Spontaneous Breaking of Lorentz and CPT Symmetry
One possible ramification of unified theories of nature such as string theory
that may underlie the conventional standard model is the possible spontaneous
breakdown of Lorentz and CPT symmetry. In this talk, the formalism for
inclusion of such effects into a low-energy effective field theory is
presented. An extension of the standard model that includes Lorentz- and
CPT-breaking terms is developed. The restriction of the standard model
extension to the QED sector is then discussed.Comment: Talk presented at Non-Accelerator New Physics, Dubna, Russia, July
199
Low temperature ferromagnetic properties of the diluted magnetic semiconductor Sb2-xCrxTe3
We report on magnetic and electrical transport properties of Sb2-xCrxTe3
single crystals with 0 <= x <= 0.095 over temperatures from 2 K to 300 K. A
ferromagnetic state develops in these crystals at low temperatures with Curie
temperatures that are proportional to x (for x > 0.014), attaining a maximum
value of 20 K for x = 0.095. Hysteresis below TC for applied field parallel to
the c-axis is observed in both magnetization and Hall effect measurements.
Magnetic as well as transport data indicate that Cr takes the 3+ (3d3) valence
state, substituting for antimony in the host lattice structure, and does not
significantly affect the background hole concentration. Analysis of the
anomalous Hall effect reveals that skew scattering is responsible for its
presence. These results broaden the scope of ferromagnetism in the V2-VI3
diluted magnetic semiconductors (DMS) and in ferromagnetic DMS structures
generallyComment: 24 pages, 5 figures, submitted to PR
CPT and Lorentz Tests in Penning Traps
A theoretical analysis is performed of Penning-trap experiments testing CPT
and Lorentz symmetry through measurements of anomalous magnetic moments and
charge-to-mass ratios. Possible CPT and Lorentz violations arising from
spontaneous symmetry breaking at a fundamental level are treated in the context
of a general extension of the SU(3) x SU(2) x U(1) standard model and its
restriction to quantum electrodynamics. We describe signals that might appear
in principle, introduce suitable figures of merit, and estimate CPT and Lorentz
bounds attainable in present and future Penning-trap experiments. Experiments
measuring anomaly frequencies are found to provide the sharpest tests of CPT
symmetry. Bounds are attainable of approximately in the
electron-positron case and of for a suggested experiment with
protons and antiprotons. Searches for diurnal frequency variations in these
experiments could also limit certain types of Lorentz violation to the level of
in the electron-positron system and others at the level of
in the proton-antiproton system. In contrast, measurements comparing
cyclotron frequencies are sensitive within the present theoretical framework to
different kinds of Lorentz violation that preserve CPT. Constraints could be
obtained on one figure of merit in the electron-positron system at the level of
, on another in the proton-antiproton system at , and on a
third at using comparisons of ions with antiprotons.Comment: 31 pages, published in Physical Review
A Clinical Investigation of Motivation to Change Standards and Cognitions about Failure in Perfectionism
Background: Clinical perfectionism is a transdiagnostic process that has been found to maintain eating disorders, anxiety disorders and depression. Cognitive behavioural models explaining the maintenance of clinical perfectionism emphasize the contribution of dichotomous thinking and resetting standards higher following both success and failure in meeting their goals. There has been a paucity of research examining the predictions of the models and motivation to change perfectionism. Motivation to change is important as individuals with clinical perfectionism often report many perceived benefits of their perfectionism; they are, therefore, likely to be ambivalent regarding changing perfectionism. Aims: The aim was to compare qualitative responses regarding questions about motivation to change standards and cognitions regarding failure to meet a personal standard in two contrasting groups with high and low negative perfectionism. Negative perfectionism refers to concern over not meeting personal standards. Method: A clinical group with a range of axis 1 diagnoses who were elevated on negative perfectionism were compared to a group of athletes who were low on negative perfectionism. Results: Results indicated that the clinical group perceived many negative consequences of their perfectionism. They also, however, reported numerous benefits and the majority stated that they would prefer not to change their perfectionism. The clinical group also reported dichotomous thinking and preferring to either keep standards the same or reset standards higher following failure, whilst the athlete group reported they would keep standards the same or set them lower. Conclusions: The findings support predictions of the cognitive behavioural model of clinical perfectionism
Neighbourhood, Route and Workplace-Related Environmental Characteristics Predict Adults' Mode of Travel to Work
Commuting provides opportunities for regular physical activity which can reduce the risk of chronic disease. Commuters' mode of travel may be shaped by their environment, but understanding of which specific environmental characteristics are most important and might form targets for intervention is limited. This study investigated associations between mode choice and a range of objectively assessed environmental characteristics.Participants in the Commuting and Health in Cambridge study reported where they lived and worked, their usual mode of travel to work and a variety of socio-demographic characteristics. Using geographic information system (GIS) software, 30 exposure variables were produced capturing characteristics of areas around participants' homes and workplaces and their shortest modelled routes to work. Associations between usual mode of travel to work and personal and environmental characteristics were investigated using multinomial logistic regression.Of the 1124 respondents, 50% reported cycling or walking as their usual mode of travel to work. In adjusted analyses, home-work distance was strongly associated with mode choice, particularly for walking. Lower odds of walking or cycling rather than driving were associated with a less frequent bus service (highest versus lowest tertile: walking OR 0.61 [95% CI 0.20–1.85]; cycling OR 0.43 [95% CI 0.23–0.83]), low street connectivity (OR 0.22, [0.07–0.67]; OR 0.48 [0.26–0.90]) and free car parking at work (OR 0.24 [0.10–0.59]; OR 0.55 [0.32–0.95]). Participants were less likely to cycle if they had access to fewer destinations (leisure facilities, shops and schools) close to work (OR 0.36 [0.21–0.62]) and a railway station further from home (OR 0.53 [0.30–0.93]). Covariates strongly predicted travel mode (pseudo r-squared 0.74).Potentially modifiable environmental characteristics, including workplace car parking, street connectivity and access to public transport, are associated with travel mode choice, and could be addressed as part of transport policy and infrastructural interventions to promote active commuting
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