434 research outputs found
Beyond the Spin Model Approximation for Ramsey Spectroscopy
Ramsey spectroscopy has become a powerful technique for probing
non-equilibrium dynamics of internal (pseudospin) degrees of freedom of
interacting systems. In many theoretical treatments, the key to understanding
the dynamics has been to assume the external (motional) degrees of freedom are
decoupled from the pseudospin degrees of freedom. Determining the validity of
this approximation -- known as the spin model approximation -- is complicated,
and has not been addressed in detail. Here we shed light in this direction by
calculating Ramsey dynamics exactly for two interacting spin-1/2 particles in a
harmonic trap. We focus on -wave-interacting fermions in quasi-one and
two-dimensional geometries. We find that in 1D the spin model assumption works
well over a wide range of experimentally-relevant conditions, but can fail at
time scales longer than those set by the mean interaction energy. Surprisingly,
in 2D a modified version of the spin model is exact to first order in the
interaction strength. This analysis is important for a correct interpretation
of Ramsey spectroscopy and has broad applications ranging from precision
measurements to quantum information and to fundamental probes of many-body
systems
Three-dimensional color code thresholds via statistical-mechanical mapping
Three-dimensional (3D) color codes have advantages for fault-tolerant quantum
computing, such as protected quantum gates with relatively low overhead and
robustness against imperfect measurement of error syndromes. Here we
investigate the storage threshold error rates for bit-flip and phase-flip noise
in the 3D color code on the body-centererd cubic lattice, assuming perfect
syndrome measurements. In particular, by exploiting a connection between error
correction and statistical mechanics, we estimate the threshold for 1D
string-like and 2D sheet-like logical operators to be and . We obtain these
results by using parallel tempering Monte Carlo simulations to study the
disorder-temperature phase diagrams of two new 3D statistical-mechanical
models: the 4- and 6-body random coupling Ising models.Comment: 4+7 pages, 6 figures, 1 tabl
A comparison of short-term and long-term air pollution exposure associations with mortality in two cohorts in Scotland
Air pollutionâmortality risk estimates are generally larger at longer-term, compared with short-term, exposure time scales. We compared associations between short-term exposure to black smoke (BS) and mortality with long-term exposureâmortality associations in cohort participants and with short-term exposureâmortality associations in the general population from which the cohorts were selected. We assessed short-to-mediumâterm exposureâmortality associations in the RenfrewâPaisley and Collaborative cohorts (using nested caseâcontrol data sets), and compared them with long-term exposureâmortality associations (using a multilevel spatiotemporal exposure model and survival analyses) and short-to-mediumâterm exposureâmortality associations in the general population (using time-series analyses). For the RenfrewâPaisley cohort (15,331 participants), BS exposureâmortality associations were observed in nested caseâcontrol analyses that accounted for spatial variations in pollution exposure and individual-level risk factors. These cohort-based associations were consistently greater than associations estimated in time-series analyses using a single monitoring site to represent general population exposure {e.g., 1.8% [95% confidence interval (CI): 0.1, 3.4%] vs. 0.2% (95% CI: 0.0, 0.4%) increases in mortality associated with 10-ÎŒg/m3 increases in 3-day lag BS, respectively}. Exposureâmortality associations were of larger magnitude for longer exposure periods [e.g., 3.4% (95% CI: â0.7, 7.7%) and 0.9% (95% CI: 0.3, 1.5%) increases in all-cause mortality associated with 10-ÎŒg/m3 increases in 31-day BS in caseâcontrol and time-series analyses, respectively; and 10% (95% CI: 4, 17%) increase in all-cause mortality associated with a 10-ÎŒg/m3 increase in geometic mean BS for 1970â1979, in survival analysis]. After adjusting for individual-level exposure and potential confounders, short-term exposureâmortality associations in cohort participants were of greater magnitude than in comparable general population time-series study analyses. However, short-term exposureâmortality associations were substantially lower than equivalent long-term associations, which is consistent with the possibility of larger, more persistent cumulative effects from long-term exposures
Realizing Exactly Solvable SU(N) Magnets with Thermal Atoms
We show that thermal fermionic alkaline-earth atoms in a flat-bottom trap
allow one to robustly implement a spin model displaying two symmetries: the
symmetry that permutes atoms occupying different vibrational levels of
the trap and the SU() symmetry associated with nuclear spin states. The
high symmetry makes the model exactly solvable, which, in turn, enables the
analytic study of dynamical processes such as spin diffusion in this SU()
system. We also show how to use this system to generate entangled states that
allow for Heisenberg-limited metrology. This highly symmetric spin model should
be experimentally realizable even when the vibrational levels are occupied
according to a high-temperature thermal or an arbitrary non-thermal
distribution.Comment: 12 pages, 5 figures (including supplemental materials
Protected gates for topological quantum field theories
We study restrictions on locality-preserving unitary logical gates for
topological quantum codes in two spatial dimensions. A locality-preserving
operation is one which maps local operators to local operators --- for example,
a constant-depth quantum circuit of geometrically local gates, or evolution for
a constant time governed by a geometrically-local bounded-strength Hamiltonian.
Locality-preserving logical gates of topological codes are intrinsically fault
tolerant because spatially localized errors remain localized, and hence
sufficiently dilute errors remain correctable. By invoking general properties
of two-dimensional topological field theories, we find that the
locality-preserving logical gates are severely limited for codes which admit
non-abelian anyons; in particular, there are no locality-preserving logical
gates on the torus or the sphere with M punctures if the braiding of anyons is
computationally universal. Furthermore, for Ising anyons on the M-punctured
sphere, locality-preserving gates must be elements of the logical Pauli group.
We derive these results by relating logical gates of a topological code to
automorphisms of the Verlinde algebra of the corresponding anyon model, and by
requiring the logical gates to be compatible with basis changes in the logical
Hilbert space arising from local F-moves and the mapping class group.Comment: 50 pages, many figures, v3: updated to match published versio
The influence of weather-type and long-range transport on airborne particle concentrations in Edinburgh, UK
This study investigated the influence of regional-scale synoptic weather type and
geographical source regions of air masses on two-particle concentration metrics
(Black Smoke (BS) and PM10) in the city of Edinburgh, UK, between 1981 and 1996.
Twenty-seven classifications of Jenkinson Daily Weather Types (JWT) were subdivided
into 9 directional categories and 3 vorticity categories, and the influence of
JWT category on BS and PM10 determined. Four-day air mass back-trajectories for 1
July 1995â30 June 1996 were computed and grouped into 8 categories depending on
the geographical route followed. Significantly elevated concentrations of BS (median
values 2, 5 and 4 ÎŒg mâ3 greater than median for 1981â1996) and PM10 (median
values 3, 5.5 and 8 ÎŒg mâ3 greater than median for 1992â1996) were observed for
anticyclonic, southerly and south-easterly weather types, respectively. These
differences were not identified at conventional levels of significance for BS in 1995â
1996. This may reflect a shift in more recent times to lower concentrations of
predominantly locally emitted BS less affected by regional scale meteorology.
Conversely, significant inter-trajectory category differences were observed for PM10
during 1995â1996, with highest concentrations associated with Eastern European
trajectories and south-easterly weather type categories (11.4 and 10.7 ÎŒg mâ3 greater
than annual means, respectively). The variation in particle concentration across
weather-type was a significant proportion of total median particle concentration, and
of a magnitude associated with adverse health outcomes. Thus current PM10
concentrations (and associated health outcomes) in Edinburgh are likely to be
significantly influenced by regional-scale meteorology independent of local air quality
management areas. Furthermore, changes in long-term trends in distributions of
synoptic weather types indicate that future climate change may influence exposure to
PM10 and the PM10:BS ratio in Edinburgh. Further definition of the relationships
between long-range transport and particle concentration will improve classification of
human exposure in epidemiological studies
How brands craft national identity
Drawing on cultural branding research, we examine how brands can craft national identity. We do so with reference to how brands enabled New Zealandâs displaced PÄkehÄ (white) majority to carve out a sense of we-ness against the backdrop of globalization and resurgent indigenous identity claims. Using multiple sources of ethnographic data, we develop a process model of how brands create national identity through we-ness. We find that marketplace actors deployed brands to create and renew perceptions of we-ness through four-stages: reification, lumping, splitting, and horizon expansion. From this, we make three primary contributions to the consumer research literature: we develop a four-part process model of how brands become national identity resources, explore the characteristics of the brands that enable the emergence of and evolution of we-ness, and explore how our processes can address a sense of dispossession among displaced-majorities in similarly defined contexts
Characterization of PM10-bound polycyclic aromatic hydrocarbons and associated carcinogenic risk in Bangkok, Thailand
Concentrations of ambient particulate-bound polycyclic aromatic hydrocarbons (pPAHs) were measured in PM10 samples collected at roadside, industrial and urban background sites in Bangkok between May 2013 and May 2014. The annual average PM10 concentrations were not significantly different between the roadside (56.4 ± 27.3 ”g mâ3) and industrial (51.0 ± 31.1 ”g mâ3) sites. The lowest annual mean PM10 was observed at the urban background site (39.8 ± 22.2 ”g mâ3). Seasonal variations of pPAHs were observed at the three sampling sites. The total pPAHs ranged between 1.09 and 13.10 ng mâ3 (mean 4.85 ± 2.51 ng mâ3), 1.49 and 9.39 ng mâ3 (mean 3.84 ± 2.01 ng mâ3) and 0.77 and 5.20 ng mâ3 (mean 2.28 ± 1.16 ng mâ3) at the roadside, industrial and urban background sites, respectively. The observed annual average benzo[a]pyrene concentrations were 0.47 ± 0.39 ng mâ3, 0.35 ± 0.27 ng mâ3 and 0.24 ± 0.19 ng mâ3 at the roadside, industrial and urban background sites. Long-term carcinogenic health risk of inhalation exposure expressed as the toxicity equivalent to benzo[a]pyrene concentrations were calculated as 0.83, 0.72 and 0.39 ng mâ3 at the industrial, roadside and urban background sites, respectively. The composition of pPAHs plays an important role in the carcinogenicity of a PAHs mixture
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