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arXiv2013

Novel techniques in VUV high-resolution spectroscopy

Novel VUV sources and techniques for VUV spectroscopy are reviewed. Laser-based VUV sources have been developed via non-linear upconversion of laser pulses in the nanosecond (ns), the picosecond (ps), and femtosecond (fs) domain, and are applied in high-resolution gas phase spectroscopic studies. While the ns and ps pulsed laser sources, at Fourier-transform limited bandwidths, are used in wavelength scanning spectroscopy, the fs laser source is used in a two-pulse time delayed mode. In addition a Fourier-transform spectrometer for high resolution gas-phase spectroscopic studies in the VUV is described, exhibiting the multiplex advantage to measure many resonances simultaneously.

physics.optics↗
arXiv2013

Atomic clocks: new prospects in metrology and geodesy

We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.

physics.atom-ph↗
arXiv2013

Antiproton low-energy collisions with Ps-atoms and true muonium atoms ($μ^+μ^-$)

Three-charge-particle collisions with participation of ultra-slow antiprotons ($\bar{\rm{p}}$) is the subject of this work. Specifically we compute the total cross sections and corresponding thermal rates of the following three-body reactions: $\bar{\rm p}+(e^+e^-) \rightarrow \bar{\rm{H}} + e^-$ and $\bar{\rm p}+(μ^+μ^-) \rightarrow \bar{\rm{H}}_μ + μ^-$, where $e^-(μ^-)$ is an electron (muon) and $e^+(μ^+)$ is a positron (antimuon) respectively, $\bar{\rm{H}}=(\bar{\rm p}e^+)$ is an antihydrogen atom and $\bar{\rm{H}}_μ=(\bar{\rm p}μ^+)$ is a muonic antihydrogen atom, i.e. a bound state of $\bar{\rm{p}}$ and $μ^+$. A set of two-coupled few-body Faddeev-Hahn-type (FH-type) equations is numerically solved in the framework of a modified close-coupling expansion approach.

physics.atom-ph↗
arXiv2013

On 1/Z expansion for two-electron systems

The $1/Z$-expansion for the Coulomb system of infinitely massive center of charge Z and two electrons is discussed. Numerical deficiency in Baker et al, {\em Phys. Rev. \bf A41}, 1247 (1990) is indicated which continue to raise doubts in correctness of their calculations of the higher order coefficients in $1/Z$-expansion expressed in Refs.[4-5]. It is shown that a minor modification of a few first coefficients found in Ref.[3] allows to calculate the ground state energies at $Z\ =\ 1, 2,\ldots \ 10$ (as well as at $Z > 10$) with a portion of 15th decimal digit in comparison with highly accurate calculations by C. Schwartz and by Nakashima-Nakatsuji. Ground state energies of two-electron ions $Z=11\ (Na^{9+})$ and $Z=12\ (Mg^{10+})$ are found with 14 decimal digits.

quant-ph↗
arXiv2013

The interference effect of laser-assisted bremsstrahlung emission in Coulumb fields of two nuclei

In this paper, the spontaneous bremsstrahlung emission from an electron scattered by two fixed nuclei in an intense laser field is investigated in details based upon the Volkov state and the Dirac-Volkov propagator. It has been found that the fundamental harmonic spectrum from the electron radiation exhibits distinctive fringes, which is dependent not only upon the internucleus distance and orientation, but also upon the initial energy of the electron and the laser intensity. By analyzing the differential cross section, we are able to explain these effects in terms of interference among the electron scattering by the nuclei. These results could have promising applications in probing the atomic or molecular dressed potentials in intense laser fields.

physics.optics↗
arXiv2013

Effective Hamiltonian for doubly excited Helium states based on four dimensional Harmonic Oscillator

Effective Hamiltonians for doubly excited Heliums states based on approximate O(4) symmetry are revised. New quantum numbers for a 4D Harmonic Oscillator are assigned to Helium states with both electrons in the n=2 shell. An effective Hamiltonian operator is constructed and optimzed by means of non-linear least-square fits to the energy levels of the Helium isoelectronic series. The results are interpreted in terms of electron correlation and a possible unified description of two-electron atom intrashell states.

physics.atom-ph↗
arXiv2013

Stability of atoms in the anionic domain (Z<N)

We study the stability and universal behaviour of the ionization energy of N-electron atoms with nuclear charge Z in the anionic domain (Z<N), considering the nuclear charge Z as an arbitrary (non-integral) parameter. HF and CISD ground state energy calculations were performed for systems with N and N-1 electrons to compute the ionization energies for nuclear charges ranging from the neutral atom region to the anionic instability threshold. As testing systems we choose inert gases (He-like, Ne-like and Ar-like isoelectronic sequences) and alkali metals (Li-like, Na-like, K-like sequences). From the results, it is apparent that, for inert gases case, the stability relation with N is completely inverted in the singly-charged anion region (Z=N-1) with respect to the neutral atom region (Z=N), i.e. larger systems are more stable than the smaller ones. We devised a semi-analytical model (inspired by the zero-range forces theory) which lead us to establish the ionization energy dependence on the nuclear charge near the threshold. This dependence is well observed in our numerical computations. Finally, we were able to describe qualitatively two universality classes for systems similar to inert gases and alkali metals, respectively.

physics.atom-ph↗
arXiv2013

Accessing interior magnetic field vector components in neutron electric dipole moment experiments via exterior measurements, I. Boundary-value techniques

We propose a new concept for determining the interior magnetic field vector components in neutron electric dipole moment experiments. If a closed three-dimensional boundary surface surrounding the fiducial volume of an experiment can be defined such that its interior encloses no currents or sources of magnetization, each of the interior vector field components and the magnetic scalar potential will satisfy a Laplace equation. Therefore, if either the vector field components or the normal derivative of the scalar potential can be measured on the surface of this boundary, thus defining a Dirichlet or Neumann boundary-value problem, respectively, the interior vector field components or the scalar potential (and, thus, the field components via the gradient of the potential) can be uniquely determined via solution of the Laplace equation. We discuss the applicability of this technique to the determination of the interior magnetic field components during the operating phase of neutron electric dipole moment experiments when it is not, in general, feasible to perform direct in situ measurements of the interior field components. We also study the specifications that a vector field probe must satisfy in order to determine the interior vector field components to a certain precision. The technique we propose here may also be applicable to experiments requiring monitoring of the vector magnetic field components within some closed boundary surface, such as searches for neutron-antineutron oscillations along a flight path or measurements in storage rings of the muon anomalous magnetic moment $g-2$ and the proton electric dipole moment.

nucl-ex↗
arXiv2013

Generation of high-frequency combs locked to atomic resonances by quantum phase modulation

A general mechanism for the generation of frequency combs referenced to atomic resonances is put forward. The mechanism is based on the periodic phase control of a quantum system's dipole response. We develop an analytic description of the comb spectral structure, depending on both the atomic and the phase-control properties. We further suggest an experimental implementation of our scheme: Generating a frequency comb in the soft-x-ray spectral region, which can be realized with currently available techniques and radiation sources. The universality of this mechanism allows the generalization of frequency-comb technology to arbitrary frequencies, including the hard-x-ray regime by using reference transitions in highly charged ions.

physics.atom-ph↗
arXiv2013

Use strong coupling strength to coherently preserve quantum entanglement

The dynamics of two qubits ultra-strongly coupled with a quantum oscillator is investigated by the adiabatic approximation method. The evolution formula of the initial four Bell states are studied under the control mechanism of the coherent state of the quantum oscillator. The influential parameters for the preservation of the entanglement are the four parameters: the average number of the coherent state, the ultra-strong coupling strength, the ratio of two frequencies of qubit and oscillator, and the inter-interaction coupling of the two qubits. The novel results show that the appropriate choice of these parameters can enable this mechanism to be utilized to preserve the entanglement of the two qubits, which is initially in the state |I_0> of the four Bell states. We give two different schemes to choose the respective parameters to maintain the entangled state |I_0> almost unchanged. The results will be helpful for the quantum information process.

quant-ph↗
arXiv2013

Three-Body Recombination in Cold Atomic Gases

Systems of three particles show a surprising feature in their bound state spectrum: a series of geometrically scaled states, known as Efimov states. These states have not yet been observed directly, but many recent experiments show indirect evidence of their existence via the so-called recombination process. The theories that predict the Efimov states also predicts either resonant enhancement of the recombination process or suppression by destructive interference, depending on the sign of the interaction between the particles. The theories predict universal features for the Efimov states, for instance that the geometric scaling factor is 22.7, meaning that one state is 22.7 times larger than its lower lying neighbour state. This thesis seeks to investigate non-universal effects by incorporating additional information about the physical interactions into the universal theories.

physics.atom-ph↗
arXiv2013

Probing Unification Scenarios with Atomic Clocks

We make use of the comparison between measurements of various pairs of atomic clocks to impose constraints on coupled variations of fundamental constants in severs unification scenarios. We obtain null results for the proton-to-electron mass ratio ${\dotμ}/μ=(0.68\pm5.79)\times10^{-16}\, {\rm yr}{}^{-1}$ and for the gyromagnetic factor ${\dot g_p}/{g_p}=(-0.72\pm0.89)\times10^{-16}\, {\rm yr}{}^{-1}$ (both of these being at the 95% confidence level). These results are compatible with theoretical expectations on unification scenarios (which we briefly describe), but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

hep-ph↗
arXiv2013

Perfect screening of the inter-polaronic interaction

We consider heavy particles immersed in a Fermi sea of light fermions, and study the interaction between the heavy particles induced by the surrounding light fermions. With the Born-Oppenheimer method, we analytically show that the induced interaction between N heavy particles vanishes for any N in the limit of high light-fermion density. The induced interaction vanishes even in the unitarity regime. This suggests that the formation of N-body bound states associated with the Efimov effect is suppressed in the presence of the dense Fermi sea. We ascribe the vanishing induced interaction to the screening effect in the neutral Fermi system.

cond-mat.quant-gas↗
arXiv2013

Angular Distribution of Electrons in Photoionization of Atoms Adsorbed on a Graphene Sheet

Within the framework of a model representing the potential of a graphene sheet U(z) as an electro-neutral layer formed by smeared carbon atoms, the effect of this potential on spectral characteristics of atoms adsorbed on a graphene sheet has been studied. Since the distance between the adsorbed atom nucleus and sheet surface significantly exceeds the radii of inner atomic shells the potential U(z) makes influence on the continuum wave functions only. Their behavior in the upper semi-space (z>0) and in the lower one (z<0) where the adsorbed atom is located is defined by a jump of the logarithmic derivative of the wave function for z=0. The photoelectron angular distributions have been calculated for different mutual positions of the polarization vector e and the axis Z normal to the sheet surface. It has been shown that the existence of the electron waves reflected from the potential U(z) leads to evident asymmetry of the angular distribution relative to the plane z=0. The experimental observation of this effect is of great interest for photoelectron spectroscopy of atoms localized on graphene structures.

physics.atom-ph↗
arXiv2013

Intermediate-energy electron-impact dissociative ionization-excitation of molecular hydrogen

We have implemented three variants of the exterior complex scaling procedure in prolate spheroidal coordinates (PS-ECS) to study the dissociative electron impact ionization-excitation of hydrogen molecule, where the emerging electrons and one of the protons are detected in coincidence for the first time in a recent experiment. In the first variant, designated PSECS-1B, the two target electrons are treated ab initio while the interaction of the incident-scattered electron is taken into account using the first term of the Born series. In the second, PSECS-2BCD, the second Born term is introduced in the dipole approximation. In the third approach, designated PSECS-SW, applied to the ionization-excitation to the $2pσ_u$ level of H$_2^+$, the multi-configurational single active electron approximation is used for the target, while the interaction of the incident electron with the target is described ab initio. Our results agree partially with those of a recent experiment which is in progress.

physics.atom-ph↗
arXiv2013

Toward Calculations with Spectroscopic Accuracy: the 2s2.2p 2Po_{3/2} - 2s2p2 4P_{5/2} Excitation Energy in Boron

No lines have been observed for transitions between the doublet and quartet levels of B I. Consequently, energy levels based on observation for the latter are obtained through extrapolation of wavelengths along the iso-electronic sequence for the 2s2.2p 2Po_{3/2} - 2s2p2 4P_{5/2} transition. In this paper, accurate theoretical excitation energies from a newly developed partitioned correlation function interaction (PCFI) method are reported for B I that include both relativistic effects in the Breit-Pauli approximation and a finite mass correction. Results are compared with extrapolated values from observed data. For B I our estimate of the excitation energy, 28959 +/- 5 cm^{-1}, is in better agreement with the values obtained by Edlén et al. (1969) than those reported by Kramida and Ryabtsev (2007). Our method is validated by applying the same procedure to the separation of these levels in C II

physics.atom-ph↗
arXiv2013

171Yb+ System Stability, 5D3/2 Hyperfine State Detection Efficiency and F=2 Lifetime

A data acquisition system is described that is designed to stabilize cooling and probe rates to maximize detection sensitivity and minimize possible systematic errors due to correlations between drifting experimental conditions and varying drive parameters. Experimental parameters that affect the Yb171 5D3/2 hyperfine state preparation and detection efficiency are characterized and optimized. A set of wait times for optimal sampling of the D3/2(F=2) lifetime is chosen and used to measure that lifetime with high statistical sensitivity. A systematic variation in this lifetime seems to be apparent. The source of the variation was not identified, but ion number and cooling rate appear to be ruled out. A net determination is made of tau=61.8ms+-(0.6)_stat+-(6.4)_sys which is significantly longer than other measurements of the same quantity. An alternate shelving scheme is proposed that would provide S-D state discrimination for Yb even isotopes as well as improved sensitivity for D state hyperfine discrimination in odd isotopes.

physics.atom-ph↗