50 research outputs found
Non-equilibrium critical scaling and universality in a quantum simulator
Universality and scaling laws are hallmarks of equilibrium phase transitions
and critical phenomena. However, extending these concepts to non-equilibrium
systems is an outstanding challenge. Despite recent progress in the study of
dynamical phases, the universality classes and scaling laws for non-equilibrium
phenomena are far less understood than those in equilibrium. In this work,
using a trapped-ion quantum simulator with single-ion resolution, we
investigate the non-equilibrium nature of critical fluctuations following a
quantum quench to the critical point. We probe the scaling of spin fluctuations
after a series of quenches to the critical Hamiltonian of a long-range Ising
model. With systems of up to 50 spins, we show that the amplitude and timescale
of the post-quench fluctuations scale with system size with distinct universal
critical exponents. While a generic quench can lead to thermal critical
behaviour, we find that a second quench from one critical state to another
(i.e. a double quench) results in critical behaviour that does not have an
equilibrium counterpart. Our results demonstrate the ability of quantum
simulators to explore universal scaling beyond the equilibrium paradigm.Comment: 10 pages, 5 figures. Supplementary information contains 18 pages, 10
figure
Broadband velocity modulation spectroscopy of HfF^+: towards a measurement of the electron electric dipole moment
Precision spectroscopy of trapped HfF^+ will be used in a search for the
permanent electric dipole moment of the electron (eEDM). While this dipole
moment has yet to be observed, various extensions to the standard model of
particle physics (such as supersymmetry) predict values that are close to the
current limit. We present extensive survey spectroscopy of 19 bands covering
nearly 5000 cm^(-1) using both frequency-comb and single-frequency laser
velocity-modulation spectroscopy. We obtain high-precision rovibrational
constants for eight electronic states including those that will be necessary
for state preparation and readout in an actual eEDM experiment.Comment: 13 pages, 7 figures, 3 table
Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center
Infrared absorption lines of H3+, including the metastable R(3,3)l line, have
been observed toward eight bright infrared sources associated with hot and
massive stars located in and between the Galactic Center Cluster and the
Quintuplet Cluster 30 pc to the east. The absorption lines with high velocity
dispersion arise in the Galaxy's Central Molecular Zone (CMZ) as well as in
foreground spiral arms. The temperature and density of the gas in the CMZ, as
determined from the relative strengths of the H3+ lines, are T=200-300K and
n=50-200cm^-3. The detection of high column densities of H3+ toward all eight
stars implies that this warm and diffuse gaseous environment is widespread in
the CMZ. The products of the ionization rate and path length for these sight
lines are 1000 and 10 times higher than in dense and diffuse clouds in the
Galactic disk, respectively, indicating that the ionization rate, zeta, is not
less than 10^-15 s^-1 and that L is at least on the order of 50 pc. The warm
and diffuse gas is an important component of the CMZ, in addition to the three
previously known gaseous environments: (1) cold molecular clouds observed by
radio emission of CO and other molecules, (2) hot (T=10^4-10^6K) and highly
ionized diffuse gas (n_e=10-100cm^-3) seen in radio recombination lines, far
infrared atomic lines, and radio-wave scattering, and (3) ultra-hot
(T=10^7-10^8K) X-ray emitting plasma. Its prevalence significantly changes the
understanding of the environment of the CMZ. The sight line toward GC IRS 3 is
unique in showing an additional H3+ absorption component, which is interpreted
as due to either a cloud associated with circumnuclear disk or the "50 km s^-1
cloud" known from radio observations. An infrared pumping scheme is examined as
a mechanism to populate the (3,3) metastable level in this cloud.Comment: 15 pages, 5 figures, 4 tables Accepted for publication in the
Astrophysical Journa
Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): study protocol for a randomized controlled trial
BACKGROUND:
Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART).
METHODS/DESIGN:
ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH2O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure 6430 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle.
DISCUSSION:
If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration metho
Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial
Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt
Quantum optics for space platforms
10.1364/OPN.23.10.000042Optics and Photonics News231042-49OPPH
Observation of Stark many-body localization without disorder
Thermalization is a ubiquitous process of statistical physics, in which
details of few-body observables are washed out in favor of a featureless steady
state. Even in isolated quantum many-body systems, limited to reversible
dynamics, thermalization typically prevails. However, in these systems, there
is another possibility: many-body localization (MBL) can result in preservation
of a non-thermal state. While disorder has long been considered an essential
ingredient for this phenomenon, recent theoretical work has suggested that a
quantum many-body system with a uniformly increasing field -- but no disorder
-- can also exhibit MBL, resulting in `Stark MBL.' Here we realize Stark MBL in
a trapped-ion quantum simulator and demonstrate its key properties: halting of
thermalization and slow propagation of correlations. Tailoring the interactions
between ionic spins in an effective field gradient, we directly observe their
microscopic equilibration for a variety of initial states, and we apply
single-site control to measure correlations between separate regions of the
spin chain. Further, by engineering a varying gradient, we create a
disorder-free system with coexisting long-lived thermalized and nonthermal
regions. The results demonstrate the unexpected generality of MBL, with
implications about the fundamental requirements for thermalization and with
potential uses in engineering long-lived non-equilibrium quantum matter