Search results for "Metas"
showing 10 items of 1693 documents
Ion storage technique for very long living states: The decay rate of the 5D 3/2 state of Ba II
1979
The metastable 5D 3/2 state of Ba+ is used to demonstrate the possibility of the ion storage technique for the measurement of extremely long lived states. The ions are confined in a r.f. quadrupole trap and excited by a strong pulsed tunable dye laser to the 6P 1/2 state which partially decays into the 5D 3/2 state. Sampling of the time development of the ground state population leads to the determination of the 5D 3/2 decay rate. Using He as a buffer gas at a pressure of about 10−6 mbar to initially store the ions, varying the gas density and extrapolating to zero pressure, we find for the lifetime $$\tau _{D_{3/2} } = 17.5 \pm 4s$$ .
Interdisciplinary experiments with polarized 3He
1998
Abstract Optical pumping of metastable 3 He atoms is a very efficient method to produce large quantities of nuclear spin-polarized 3 He. Recent developments in mechanical compression of the gas, its storage and transport allow for its flexible use in different fields of physics and applied science. Among these are (1) scattering experiments of polarized beams from polarized 3 He-targets, (2) 3 He as neutron spin filter to polarize neutron beams at research reactors, and (3) polarized 3 He gas inhaled into the lungs to perform magnetic resonance imaging. The paper discusses the different topics along with results obtained in a first round of experiments.
Statistical Theories of Phase Transitions
2013
The sections in this article are Introduction Phenomenological Concepts Order Parameters and the Landau Symmetry Classification Second-Order Transitions and Concepts about Critical Phenomena (Critical Exponents, Scaling Laws, etc.) Second-Order Versus First-Order Transitions; Tricritical and other Multicritical Phenomena Dynamics of Fluctuations at Phase Transitions Effects of Surfaces and of Quenched Disorder on Phase Transitions: A Brief Overview Computational Methods Dealing with the Statistical Mechanics of Phase Transitions and Phase Diagrams Models for Order–Disorder Phenomena in Alloys Molecular Field Theory and its Generalization (Cluster Variation Method, etc) Computer Simulation T…
Stabilization of quantum metastable states by dissipation
2015
Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. Here we show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable state has a nonmonotonic behavior versus the system-bath coupling and the temperature, producing a stabilizing effect.
Stabilization by dissipation and stochastic resonant activation in quantum metastable systems
2018
In this tutorial paper we present a comprehensive review of the escape dynamics from quantum metastable states in dissipative systems and related noise-induced effects. We analyze the role of dissipation and driving in the escape process from quantum metastable states with and without an external driving force, starting from a nonequilibrium initial condition. We use the Caldeira–Leggett model and a non-perturbative theoretical technique within the Feynman–Vernon influence functional approach in strong dissipation regime. In the absence of driving, we find that the escape time from the metastable region has a nonmonotonic behavior versus the system-bath coupling and the temperature, produci…
A simple method for counting the number of trapped ions in an ion trap
1996
The number of stored Ca\(^+\) ions in an ion trap was measured optically by utilizing the metastable states. All the ions trapped are first pumped into the metastable \(D\) states. The ions in the metastable \(D\) states are transferred to the ground \(S\) state via the \(P\) state by exciting a \(D\rightarrow P\) transition. Each ion then emits one photon through a subsequent \(P\rightarrow S\) spontaneous emission. Thus, the number of photons is the same as the number of trapped ions initially in the metastable states. When a fraction of all the stored ions are pumped into the metastable states, the method is still applicable if the fraction of the ions is known.
Theory of first-order phase transitions
1987
An introductory review of various concepts about first-order phase transitions is given. Rules for classification of phase transitions as second or first order are discussed, as well as exceptions to these rules. Attention is drawn to the rounding of first-order transitions due to finite-size or quenched impurities. Computational methods to calculate phase diagrams for simple model Hamiltonians are also described. Particular emphasis is laid on metastable states near first-order phase transitions, on the 'stability limits' of such states (e.g. the 'spinodal curve' of the gas-liquid transition) and on the dynamic mechanisms by which metastable states decay (nucleation and growth of droplets …
Collisional de-excitation of the metastableD-states of Ba+ by He, Ne, N2 and H2
1989
The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba+ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P1/2 or 6P3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H2 and N2 we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10−13cm3/s, 〈σ·υ〉 (Ne)=5.1±0.4·10−13cm3/s, 〈σ·υ〉 (…
Direct time delay computation applied to the O + O2 exchange reaction at low energy: Lifetime spectrum of O3* species
2021
We report full quantum dynamical calculations for lifetimes of scattering resonances, among which are true metastable states, of the intermediate heavy ozone complex 50O3* of the 18O + 16O16O reaction, for any value of the total angular momentum quantum number J. We show that computations for nonzero values of J are mandatory in order to properly analyze resonances and time delays, with a view to establish a somewhat comprehensive eigenlife spectrum of the complex O3*. Calculations have been performed in a given low to moderate energy range, including the interval between zero-point energies (ZPEs) of reagents and product species. Quasi-bound states tend to be more numerous, and eigenlifeti…
Spin stiffness of vector spin glasses
2011
Abstract We study domain-wall excitations for O ( m ) vector spin glasses in the limit m → ∞ , where the energy landscape is simplified considerably compared to XY or Heisenberg models due to the complete disappearance of metastability. Using numerical ground-state calculations and appropriate pairs of complementary boundary conditions, domain-wall defects are inserted into the systems and their excitation energies are measured. This allows us to determine the stiffness exponents for lattices of a range of spatial dimensions d = 2 , … , 7 . Compiling these results, we can finally determine the lower critical dimension of the model. The outcome is compared to estimates resulting from field-t…