Atomic Lifetimes Research Articles

Non-nearest neighbour ICD in clusters

Interatomic Coulombic decay (ICD) is an electronic decay process of excited, ionized systems. It has been shown to occur in a multitude of small and large systems. The effects of more than one possible decay partner are discussed in detail illustrated by simulated ICD electron spectra of NeAr clusters and pure Ne clusters. Hereby, the mostly underestimated contribution of decay with non-nearest neighbours is highlighted. In the neon clusters, the lifetime of the bulk atoms is found to be in excellent agreement with experiment (Jahnke et al 2004 Phys. Rev. Lett. 93 173401) while the lifetimes of the surface atoms differ significantly. Hence, the experimental lifetime can not purely be explained by the effect of the number of neighbours. We propose the possibility to investigate the transition from small clusters to the solid state by using the ICD electron spectra to distinguish between icosahedral and cuboctahedral cluster structures.

Controlling spin relaxation with a cavity.

Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the rate of spontaneous emission can be greatly enhanced by placing the quantum system in a resonant cavity. This effect has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, and is essential for the realization of high-efficiency single-photon sources. Here we report the application of this idea to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity with a high quality factor and a small mode volume, we reach the regime in which spontaneous emission constitutes the dominant mechanism of spin relaxation. The relaxation rate is increased by three orders of magnitude as the spins are tuned to the cavity resonance, demonstrating that energy relaxation can be controlled on demand. Our results provide a general way to initialize spin systems into their ground state and therefore have applications in magnetic resonance and quantum information processing. They also demonstrate that the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point at which quantum fluctuations have a marked effect on the spin dynamics; as such, they represent an important step towards the coherent magnetic coupling of individual spins to microwave photons.

The investigation ofK+π−,π+K−andπ+π−atoms

Theory, using Low Energy QCD, predicts with high precision the pion-pion and pion-kaon scattering lengths. There is accurate relation between K + π − and π + K − atoms lifetime and pion-kaon S-wave scattering lengths with isospin 1/2 and 3/2. Experiment DIRAC at CERN PS detects 345 ± 61 pairs from K + π − and π + K − atoms breakup. It allows to achieve the first observation of exotic atoms consisted of pion and kaon. Measured values of πK atom lifetime and corresponding pion-kaon scattering length difference are presented. It is shown, that experimental accuracy for pion-kaon scattering length difference could be significantly improved with an experiment at SPS energy.

Detection of the carcinogenic properties of synthetic and natural dyes using positron annihilation lifetime spectrometry.

Positron annihilation lifetime spectrometry was used to detect the carcinogenic properties of a range of synthetic and natural dyes used in the food and drug industries. This technique is based on the electrophilic character of carcinogens and the sensitivity of positron annihilation lifetime spectrometry, in which the lifetime of the exotic positronium atom is dependent on the electron density environment. Differences between the annihilation times of some synthetic and natural dyes were examined. The obtained data were compared with the boundary values for the lifetime of positronium, which has previously been shown to be able to divide substances into carcinogens and non-carcinogens.

852-nm triggered single-photon source based on trapping and manipulation of a single cesium atom confined in a microscopic optical dipole trap

Single-atom-based single-photon source has several advantages, such as narrow bandwidth, wavelength matching with the absorption line of the same atomic ensemble, and insensitivity to the environment disturbing, and it is very important not only for basic researches in quantum optic field but also for applications in quantum information processing. In this paper, we report the generation of a 10-MHz-repetition-rate triggered single-photon source at 852 nm based on a trapped single cesium atom in a far-off-resonance microscopic optical dipole trap (FORT). To generate an optical dipole trap, a far-red-detuned 1064 nm laser beam is tightly focused by using a high numerical aperture lens, a typical trap depth is 2 mK and trap waist is 2.3 m. To obtain a maximum probability of pulsed excitation, the frequency of the pulsed laser should be resonant with the atomic energy levels and the trapped single atom must be excited with a -pulse. However, the interaction between the FORT laser and the atoms causes AC Stark shifts of the atomic energy levels. Thus, in order to demonstrate the resonant pulsed excitation, it is important to calculate and measure the shift of 6S1/2|Fg=4,mF=+4-6P3/2|Fe=5,mF=+5 cyclical transition in the FORT. For a two-level system, the probability of pulsed excitation can be described by Rabi oscillations with a characteristic Rabi frequency . With an optimized time sequence, we experimentally demonstrate the Rabi oscillation between the ground state and the excited state, and the peak power of -pulse laser is about 1.25 mW. We also measure the temporal envelope of single photons after a -pulse excitation. A gated pulsed excitation and cooling technique are used to reduce the possibility that atoms are heated by -pulse laser. The typical trapping lifetime of single cesium atom is extended from~108 ups to~2536 ms. The corresponding number of excitations is improved from 108 to 360000. The second-order intensity correlations of the emitted single-photon are characterized by implementing Hanbury Brown-Twiss setup. The statistics shows a strong anti-bunching with a value of 0.09 for the second-order correlation at zero delay. In the future, we will perform a Hong-Ou-Mandel two-photon interference experiment to analyze the indistinguishability of the single photons. We will also trap single atoms in a magic-wavelength optical dipole trap where the ground and the excited states have the same shift.

Cooperative Emission of a Pulse Train in an Optically Thick Scattering Medium.

An optically thick cold atomic cloud emits a coherent flash of light in the forward direction when the phase of an incident probe field is abruptly changed. Because of cooperativity, the duration of this phenomena can be much shorter than the excited lifetime of a single atom. Repeating periodically the abrupt phase jump, we generate a train of pulses with short repetition time, high intensity contrast, and high efficiency. In this regime, the emission is fully governed by cooperativity even if the cloud is dilute.

Extended Ehrenfest theorem with radiative corrections

A set of basic evolution equations for the mean values of dynamical variables is obtained from the Fokker–Planck equation applied to the general problem of a particle subject to a random force. The specific case of stochastic electrodynamics is then considered, in which the random force is due to the zero-point radiation field. Elsewhere it has been shown that when this system reaches a state of energy balance, it becomes controlled by an equation identical to Schrödinger’s, if the radiationless approximation is made. The Fokker–Planck equation was shown to lead to the Ehrenfest theorem under such an approximation. Here we show that when the radiative terms are not neglected, an extended form of the Ehrenfest equation is obtained, from which follow, among others, the correct formulas for the atomic lifetimes and the (nonrelativistic) Lamb shift.

Probing the quantum vacuum with an artificial atom in front of a mirror

Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons flitting in and out of existence, they still have a very real impact, \emph{e.g.}, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a "mirror", creating regions in space where they are suppressed. As we then effectively move an artificial atom in and out of these regions, measuring the atomic lifetime tells us the strength of the fluctuations. The weakest fluctuation strength we observe is 0.02 quanta, a factor of 50 below what would be expected without the mirror, demonstrating that we can hide the atom from the vacuum.

Measuring excited state lifetime of Rb atoms with pump-probe technique

A technique for measuring the excited state lifetime τex of optical transitions in alkali atoms is presented. It is a form of pump-probe technique based on time-resolved optical transmission through the atomic vapor cell. This technique can serve as an alternative to the traditionally used time-resolved photofluorescence methods when measuring alkali vapor cells with heavily quenched fluorescence, where the τex is expected to be on the order of a few nanoseconds, and the highly sensitive fluorescence detectors with sub-nanosecond temporal resolution that are required may not be available. We use this technique to measure the τex of Rb atoms in vapor cells with different buffer gas pressures.

Mass scaling in photoassociation of spin-singlet atoms

SynopsisPhotoassociation spectroscopy, based on forming of molecules from colliding atoms in the presence of light, is a priceless tool for the study of atomic interactions. It enables direct measurements of bound state energies, both in excited and ground state molecules. Applications include determinations of s-wave scattering lengths, as well as atomic state lifetimes. In this work we present the results of our research on the mass-scaling behaviour of molecular bound state energies and collisional properties in spin-singlet atoms. We will concentrate on two such species: strontium and ytterbium, both of which offer several stable isotopes, enabling mass tuning of the system's properties.

Semi-empirical studies of atomic transition probabilities, oscillator strengths and radiative lifetimes in Hf II

Over the past few years, laser induced fluorescence and Fourier Transform techniques have been applied to measure radiative lifetimes and branching fractions in Hf II in order to derive oscillator strengths and transition probabilities. In the present work, we propose to compare for the first time these experimental data to computed values obtained by two different semi-empirical approaches, respectively based on a parametrization of the oscillator strengths and on a pseudo-relativistic Hartree–Fock model including core-polarization effects. The overall agreement between all sets of data is found to be good. We furthermore give radial integrals of the main atomic transitions in this study: 〈5d6s6p|r1|5d26s〉=0.1504 (0.0064), 〈6s26p|r1|5d6s2〉=1.299 (0.012), 〈5d26p|r1|5d26s〉=−0.298 (0.013), 〈5d26p|r1|5d3〉=2.025 (0.027). Finally a new set of oscillator strengths and transition probabilities is reported for many transitions in Hf II.

Sapphire: a better material for atomization and in situ collection of silver volatile species for atomic absorption spectrometry

Sapphire is presented as a high temperature and corrosion resistant material of an optical tube of an atomizer for volatile species of Ag generated by the reaction with NaBH4. The modular atomizer design was employed which allowed to carry out the measurements in two modes: (i) on-line atomization and (ii) in situ collection (directly in the optical tube) by means of excess of O2 over H2 in the carrier gas during the trapping step and vice versa in the volatilization step. In comparison with quartz atomizers, the sapphire tube atomizer provides a significantly increased atomizer lifetime as well as substantially improved repeatability of the Ag in situ collection signals shapes. In situ collection of Ag in the sapphire tube atomizer was highly efficient (>90%). Limit of detection in the on-line atomization mode and in situ collection mode, respectively, was 1.2ngml−1 and 0.15ngml−1.

π K atom lifetime and π K scattering length measurements

π K atom lifetime and π K scattering length measurements

Blood pressure, left ventricular geometry, and systolic function in children exposed to inorganic arsenic.

Background:Inorganic arsenic (iAs) is a ubiquitous element present in the groundwater worldwide. Cardiovascular effects related to iAs exposure have been studied extensively in adult populations. Few epidemiological studies have been focused on iAs exposure–related cardiovascular disease in children.Objective:In this study we investigated the association between iAs exposure, blood pressure (BP), and functional and anatomical echocardiographic parameters in children.Methods:A cross-sectional study of 161 children between 3 and 8 years was conducted in Central Mexico. The total concentration of arsenic (As) species in urine (U-tAs) was determined by hydride generation–cryotrapping–atomic absorption spectrometry and lifetime iAs exposure was estimated by multiplying As concentrations measured in drinking water by the duration of water consumption in years (LAsE). BP was measured by standard protocols, and M-mode echocardiographic parameters were determined by ultrasonography.Results:U-tAs concentration and LAsE were significantly associated with diastolic (DBP) and systolic blood pressure (SBP) in multivariable linear regression models: DBP and SBP were 0.013 (95% CI: 0.002, 0.024) and 0.021 (95% CI: 0.004, 0.037) mmHg higher in association with each 1-ng/mL increase in U-tAs (p < 0.025), respectively. Left ventricular mass (LVM) was significantly associated with LAsE [5.5 g higher (95% CI: 0.65, 10.26) in children with LAsE > 620 compared with < 382 μg/L-year; p = 0.03] in an adjusted multivariable model. The systolic function parameters left ventricular ejection fraction (EF) and shortening fraction were 3.67% (95% CI: –7.14, –0.20) and 3.41% (95% CI: –6.44, –0.37) lower, respectively, in children with U-tAs > 70 ng/mL compared with < 35 ng/mL.Conclusion:Early-life exposure to iAs was significantly associated with higher BP and LVM and with lower EF in our study population of Mexican children.Citation:Osorio-Yáñez C, Ayllon-Vergara JC, Arreola-Mendoza L, Aguilar-Madrid G, Hernández-Castellanos E, Sánchez-Peña LC, Del Razo LM. 2015. Blood pressure, left ventricular geometry, and systolic function in children exposed to inorganic arsenic. Environ Health Perspect 123:629–635; http://dx.doi.org/10.1289/ehp.1307327

Experimental research on loading strontium bosons into the optical lattice operating at the “magic” wavelength

The optical lattice clock with neutral atoms occupies an outstanding position in the research field of atomic clocks, demonstrating the great potential of its performance (like the uncertainty and the stability). At present, the optical lattice clock has realized a 10-18 level of its uncertainty. In this paper, we present the realization of loading bosonic atoms 88Sr (strontium, alkaline-earth metals) into a one-dimensional (1D) optical lattice in our laboratory. The optical lattice where the atoms are trapped can make the energy level shift, called Stark shift. But there is the special optical lattice operating at the “magic” wavelength for clock transitions (5s2) 1S0-(5s5p) 3P0, which can make the same Stark light-shift for both of them, indicating a zero light-shift relative to the clock. In our experiment, Sr atoms are cooled in a two-stage cooling and its temperature can be as low as 2 μK. Then these cold atoms are confined in the Lamb-Dicke region by the lattice laser output from an amplified diode laser operating at the “magic” wavelength, 813 nm. Experimentally, it is straightforward to provide 850 mW of lattice power focused to a 38 μm beam radius. After the cold atoms have trapped in the optical lattice, the lifetime of atoms in 1D optical lattice is measured to be 270 ms. The temperature and the number are about 3.5 μK and 1.2×105 respectively. Besides, effects of the power of the lattice laser on both the number and temperature are analyzed. The number changes linearly with the laser power, while there is no obvious influence on the temperature by the power. This original and special approach for atoms trapped in the optical lattice can provide a long interrogation time for probing the clock transition. Furthermore, it may be the foundation for developing our optical lattice clock of strontium atoms.

Atomic structure, radiative lifetime and oscillator strength calculations in doubly ionized molybdenum (Mo iii)

Radiative lifetimes, transition probabilities and oscillator strengths in doubly ionized molybdenum (Mo iii) are reported for the first time in the present paper. This new set of atomic data has been obtained by using a semi-empirical computational technique based on the pseudo-relativistic Hartree–Fock approach in which a large amount of intravalence and core–valence electron correlations were included. In view of the lack of theoretical and experimental data available in the literature for this ion, the reliability of the results obtained in our work is discussed on the basis of comparisons with the isoelectronic ion Nb ii for which an investigation was recently performed using a similar method (Nilsson et al 2010 Astron. Astrophys. 511 A16).

Thermal equilibrium/disequilibrium features in the excited-state temperature of atomic helium in MAP-II divertor simulator

Doppler–Stark spectrometry and laser Thomson scattering diagnostics for helium plasmas were applied to the MAP-II (material and plasma) steady-state linear divertor simulator at the University of Tokyo. In recombining plasmas, as the volumetric recombination proceeded, atomic, ionic and electron temperatures converged to the same values, which indicated the achievement of thermal equilibrium. On the other hand, in ionizing plasmas, in addition to the collisional heating of bulk atoms, excess heating of atoms in the high principal quantum number states (above Griem’s boundary) was observed. This disequilibrium feature can be attributed to the presence of two prevailing conditions: that the characteristic time of the charge-exchange process of the atoms with ions in the system became shorter than the lifetime of the excited atoms spent above Griem’s boundary, and that the population influx from above Griem’s boundary is considerably larger than that from below the boundary.

3D modeling of magnetic atom traps on type-II superconductor chips

Magnetic traps for cold atoms have become a powerful tool in cold atom physics and condensed matter research. The traps on superconducting chips allow one to increase the trapped atom lifetime and coherence time by decreasing the thermal noise by several orders of magnitude compared to that of the typical normal-metal conductors. A thin superconducting film in the mixed state is, usually, the main element of such a chip. Using a finite element method to analyze thin film magnetization and transport current in type-II superconductivity, we study magnetic traps recently employed in experiments. The proposed approach allows us to predict important characteristics of the magnetic traps (their depth, shape, distance from the chip surface, etc) that are necessary when designing magnetic traps in cold atom experiments.

E1-forbidden transition rates in ions of astrophysical interest

Transition rates in atomic systems may appear to be of little importance in steady-state plasmas that are observed at great distances from Earth. However, some of the transition rates compete with collision rates, and in these cases certain line intensity ratios are affected and can serve as remote indicators of density. In the low-density environments of stellar coronae and planetary nebulae, the transition rates of interest are mostly spin-forbidden E1 decays, higher-multipole order transitions (M1, E2, M2, M3), and hyperfine-induced transitions. On Earth, measurements of the long upper level lifetimes of these atomic systems require the use of ion traps. A fair number of test cases with lifetimes in the range from nanoseconds to many seconds have been treated successfully, and the evolution of calculations along with the experimental progress is notable. A new generation of cold ion traps is expected to extend the atomic lifetime measurements on multiply charged ions into the range of many minutes.

Experimental and numerical investigation of time evolution of discharge current and optical emission in helium–nitrogen cryoplasmas

Cryoplasmas represent a class of non-equilibrium plasmas whose gas temperature can be controlled below room temperature. However, so far, the influence of the plasma gas temperature on the plasma chemical reactions has not yet been examined in detail. Here we investigated the time-dependent reaction dynamics related to optical emission in helium–nitrogen cryoplasmas. We acquired voltage and discharge current waveforms, optical emission spectra, and observed a temporal change of the emission intensity in helium–nitrogen cryoplasmas at two experimental conditions (temperatures of temperature detector: 5 K and plasma gas temperature: 28 K (condition A), 40 K and 54 K (condition B)). Two time-dependent phenomena were observed: the first was a longer duration of the discharge current compared to that of helium emission at both conditions A and B, and the second was nitrogen ion emission delayed by about 8 µs with respect to the emissions of atomic helium and helium dimers at 40 K. The experimental observations could be reproduced qualitatively by a global reaction model, which took into account the effect of the plasma gas temperature on the reaction rate constants and the diffusion coefficients. The simulations suggested that the reactions related to metastable helium atom were the key reactions, and that the long lifetimes of metastable helium atoms at cryogenic gas temperatures are crucial for the appearance of the time-dependent phenomena. These results imply that the plasma gas temperature is one of the key parameters in non-equilibrium plasma chemistry.