arXiv subjects

M. S. Safronova

Publications and source records attributed to M. S. Safronova.

At least 109 records · Page 6Linked to original sources

arXiv2012

Magic wavelengths for optical cooling and trapping of lithium

Using first-principles calculations, we identify magic wavelengths for the 2s-2p and 2s-3p transitions in lithium. The ns and np atomic levels have the same ac Stark shifts at the corresponding magic wavelength, which facilitates state-insensitive optical cooling and trapping. Tune-out wavelengths for which the ground-state frequency-dependent polarizability vanishes are also calculated. Differences of these wavelengths between 6Li and 7Li are reported. Our approach uses high-precision, relativistic all-order methods in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Recommended values are provided for a large number of Li electric-dipole matrix elements. Static polarizabilities for the 2s, 2p, 3s, 3p, and 3d levels are compared with other theory and experiment where available. Uncertainties of all recommended values are estimated. The magic wavelengths for the uv 2s-3p transition are of particular interest for the production of a quantum gas of lithium [Duarte et al., Phys. Rev. A 84, 061406R (2011)].

physics.atom-ph↗

arXiv2012

Polarizabilities of Si^{2+}: a benchmark test of theory and experiment

We have calculated electric-dipole polarizabilities of the 3s^2 ^1S_0, 3s3p ^3P_0, and 3s3p ^1P_1 states of the Si^{2+} ion using recently developed configuration interaction + all-order method. Detailed evaluation of the uncertainties of the final results is carried out. Our value for the ground state electric-dipole polarizability 11.670(13) a.u. is in excellent agreement with the resonant excitation Stark ionization spectroscopy value 11.669(9) a.u. [Komara et al., J. Phys. B 38, 87 (2005); Mitroy, Phys. Rev. A 78, 052515 (2008)]. This work represents the most precise benchmark test to date of theory and experiment in divalent atoms. The near cancellation of the ns^2 ^1S_0 ground state and the lowest nsnp ^3P_0 polarizabilities previously observed in B+, Al+, In+, Tl+, and Pb^{2+} is also found in Si^{2+} ion.

physics.atom-ph↗

arXiv2012

Study of quadrupole polarizabilities with combined configuration interaction and coupled-cluster method

The recently developed method combining the configuration interaction and the coupled-cluster method was demonstrated to provide accurate treatment of correlation corrections in divalent atomic systems [M.S.Safronova, M.G.Kozlov, and C.W.Clark, Phys. Rev. Lett. 107, 143006 (2011)]. We have extended this approach to the calculation of quadrupole polarizabilities alpha_2 and applied it to evaluate alpha_2 for the ground state of Mg and Mg-like Si^{2+}. Performing the calculations in three different approximations of increasing accuracy allowed us to place the upper bounds on the uncertainty of the final results. The recommended values alpha_2(3s^2 1S0)= 35.86(13) a.u. for Si^{2+} and alpha_2(3s^2 1S0)= 814(3) a.u. for Mg are estimated to be accurate to 0.37%. Differences in quadrupole polarizability contributions in neutral Mg and Si^{2+} ion are discussed.

physics.atom-ph↗

arXiv2012

Anomalously small blackbody radiation shift in Tl+ frequency standard

The operation of atomic clocks is generally carried out at room temperature, whereas the definition of the second refers to the clock transition in an atom at absolute zero. This implies that the clock transition frequency should be corrected in practice for the effect of finite temperature of which the leading contributor is the blackbody radiation (BBR) shift. In the present work, we used configuration interaction + coupled-cluster method to evaluate polarizabilities of the $6s^2 ^1S_0$ and $6s6p ^3P_0$ states of Tl$^+$ ion; we find $α_0(^1S_0)=19.6$ a.u. and $α_0(^3P_0)=21.4$ a.u.. The resulting BBR shift of the $6s6p ^3P_0 - 6s^2 ^1S_0$ Tl$^+$ transition at $300 K$ is $Δν_{\rm BBR}=-0.0157(16)$ Hz. This result demonstrates that near cancelation of the $^1S_0$ and $^3P_0$ state polarizabilities in divalent B+, Al+, In$^+$ ions of group IIIB [Safronova \textit{et al.}, PRL 107, 143006 (2011)] continues for much heavier Tl$^+$, leading to anomalously small BBR shift for this system. This calculation demonstrates that the BBR contribution to the fractional frequency uncertainty of the Tl+ frequency standard at 300K is $1\times10^{-18}$. We find that Tl+ has the smallest fractional BBR shift among all present or proposed frequency standards with the exception of Al+.

physics.atom-ph↗

arXiv2012

Electric dipole moment enhancement factor of thallium

The goal of this work is to resolve the present controversy in the value of the EDM enhancement factor of Tl. We have carried out several calculations by different high-precision methods, studied previously omitted corrections, as well as tested our methodology on other parity conserving quantities. We find the EDM enhancement factor of Tl to be equal to -573(20). This value is 20% larger than the recently published result of Nataraj et al. [Phys. Rev. Lett. 106, 200403 (2011)], but agrees very well with several earlier results.

physics.atom-ph↗

arXiv2011

Precision calculation of blackbody radiation shifts for optical frequency metrology

We show that three group IIIB divalent ions, B+, Al+, and In+, have anomalously small blackbody radiation (BBR) shifts of the ns^2 1S0 - nsnp 3P0 clock transitions. The fractional BBR shifts for these ions are at least 10 times smaller than those of any other present or proposed optical frequency standards at the same temperature, and are less than 0.3% of the Sr clock shift. We have developed a hybrid configuration interaction + coupled-cluster method that provides accurate treatment of correlation corrections in such ions, considers all relevant states in the same systematic way, and yields a rigorous upper bound on the uncertainty of the final results. We reduce the BBR contribution to the fractional frequency uncertainty of the Al+ clock to 4 \times 10^{-19} at T=300K. We also reduce the uncertainties due to this effect at room temperature to 10^{-18} level for B+ and In+ to facilitate further development of these systems for metrology and quantum sensing. These uncertainties approach recent estimates of the feasible precision of currently proposed optical atomic clocks.

physics.atom-ph↗

arXiv2011

Magic-zero wavelengths of alkali-metal atoms and their applications

Using first-principles calculations, we identify "magic-zero" optical wavelengths, λ_zero, for which the ground-state frequency-dependent polarizabilities of alkali-metal atoms vanish. Our approach uses high-precision, relativistic all-order methods in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. We discuss the use of magic-zero wavelengths for sympathetic cooling in two-species mixtures of alkalis with group-II and other elements of interest. Special cases in which these wavelengths coincide with strong resonance transitions in a target system are identified.

physics.atom-ph↗

arXiv2011

Resolving all-order method convergence problems for atomic physics applications

The development of the relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function are included to all orders of perturbation theory led to many important results for study of fundamental symmetries, development of atomic clocks, ultracold atom physics, and others, as well as provided recommended values of many atomic properties critically evaluated for their accuracy for large number of monovalent systems. This approach requires iterative solutions of the linearized coupled-cluster equations leading to convergence issues in some cases where correlation corrections are particularly large or lead to an oscillating pattern. Moreover, these issues also lead to similar problems in the CI+all-order method for many-particle systems. In this work, we have resolved most of the known convergence problems by applying two different convergence stabilizer methods, reduced linear equation (RLE) and direct inversion of iterative subspace (DIIS). Examples are presented for B, Al, Zn$^+$, and Yb$^+$. Solving these convergence problems greatly expands the number of atomic species that can be treated with the all-order methods and is anticipated to facilitate many interesting future applications.

physics.atom-ph↗

arXiv2010

Blackbody radiation shift, multipole polarizabilities, oscillator strengths, lifetimes, hyperfine constants, and excitation energies in Ca+

A systematic study of Ca+ atomic properties is carried out using high-precision relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Reduced matrix elements, oscillator strengths, transition rates, and lifetimes are determined for the levels up to n = 7. Recommended values and estimates of their uncertainties are provided for a large number of electric-dipole transitions. Electric-dipole scalar polarizabilities for the 5s, 6s, 7s, 8s, 4p, 5p, 3d, and 4d states and tensor polarizabilities for the 4p, 5p, 3d, and 4d states in Ca+ are calculated. Methods are developed to accurately treat the contributions from highly-excited states, resulting in significant (factor of 3) improvement in accuracy of the 3d_{5/2} static polarizability value, 31.8(3) a.u., in comparison with the previous calculation [Arora et al., Phys. Rev. A 76, 064501 (2007)]. The blackbody radiation (BBR) shift of the 4s - 3d_{5/2} clock transition in Ca+ is calculated to be 0.381(4) Hz at room temperature, T=300K. Electric-quadrupole 4s -nd and electric-octupole 4s -nf matrix elements are calculated to obtain the ground state multipole E2 and E3 static polarizabilities. The hyperfine constants A are determined for the low-lying levels up to n = 7. The quadratic Stark effect on hyperfine structure levels of 43Ca+ ground state is investigated. These calculations provide recommended values critically evaluated for their accuracy for a number of Ca+ atomic properties for use in planning and analysis of various experiments as well as theoretical modeling.

physics.atom-ph↗

arXiv2010

Blackbody radiation shift in 87Rb frequency standard

The operation of atomic clocks is generally carried out at room temperature, whereas the definition of the second refers to the clock transition in an atom at absolute zero. This implies that the clock transition frequency should be corrected in practice for the effect of finite temperature of which the leading contributor is the blackbody radiation (BBR) shift. Experimental measurements of the BBR shifts are difficult. In this work, we have calculated the blackbody radiation shift of the ground-state hyperfine microwave transition in 87Rb using the relativistic all-order method and carried out detailed evaluation of the accuracy of our final value. Particular care is taken to accurately account for the contributions from highly-excited states. Our predicted value for the Stark coefficient, k_S=-1.240(4)\times 10^{-10}\text{Hz/(V/m)}^{2} is three times more accurate than the previous calculation [1].

physics.atom-ph↗

arXiv2010

State-insensitive bichromatic optical trapping

We propose a scheme for state-insensitive trapping of neutral atoms by using light with two independent wavelengths. In particular, we describe the use of trapping and control lasers to minimize the variance of the potential experienced by a trapped Rb atom in ground and excited states. We present calculated values of wavelength pairs for which the 5s and 5p_{3/2} levels have the same ac Stark shifts in the presence of two laser fields.

physics.atom-ph↗

arXiv2010

Theory and applications of atomic and ionic polarizabilities

Atomic polarization phenomena impinge upon a number of areas and processes in physics. The dielectric constant and refractive index of any gas are examples of macroscopic properties that are largely determined by the dipole polarizability. When it comes to microscopic phenomena, the existence of alkaline-earth anions and the recently discovered ability of positrons to bind to many atoms are predominantly due to the polarization interaction. An imperfect knowledge of atomic polarizabilities is presently looming as the largest source of uncertainty in the new generation of optical frequency standards. Accurate polarizabilities for the group I and II atoms and ions of the periodic table have recently become available by a variety of techniques. These include refined many-body perturbation theory and coupled-cluster calculations sometimes combined with precise experimental data for selected transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index measurements in microwave cavities, ab initio calculations of atomic structures using explicitly correlated wave functions, interferometry with atom beams, and velocity changes of laser cooled atoms induced by an electric field. This review examines existing theoretical methods of determining atomic and ionic polarizabilities, and discusses their relevance to various applications with particular emphasis on cold-atom physics and the metrology of atomic frequency standards.

physics.atom-ph↗

arXiv2009

Development of a configuration-interaction + all-order method for atomic calculations

We develop a theoretical method within the framework of relativistic many-body theory to accurately treat correlation corrections in atoms with few valence electrons. This method combines the all-order approach currently used in precision calculations of properties of monovalent atoms with the configuration-interaction approach that is applicable for many-electron systems. The method is applied to Mg, Ca, Sr, Zn, Cd, Ba, and Hg to evaluate ionization energies and low-lying energy levels.

physics.atom-ph↗

arXiv2009

Blackbody-radiation shift in a 88Sr+ ion optical frequency standard

The blackbody radiation (BBR) shift of the 5s - 4d_{5/2} clock transition in 88Sr+ is calculated to be 0.250(9) Hz at room temperature, T=300K, using the relativistic all-order method where all single and double excitations of the Dirac-Fock wave function are included to all orders of perturbation theory. The BBR shift is a major component in the uncertainty budget of the optical frequency standard based on the 88Sr+ trapped ion. The scalar polarizabilities of the 5s and 4d_{5/2} levels, as well as the tensor polarizability of the 4d_{5/2} level, are presented together with the evaluation of their uncertainties. The lifetimes of the 4d_{3/2}, 4d_{5/2}, 5p_{1/2}, and 5p_{3/2} states are calculated and compared with experimental values.

physics.atom-ph↗

arXiv2009

Calculation of parity nonconserving amplitude and other properties of Ra+

We have calculated parity nonconserving 7s - 6d_{3/2} amplitude E_PNC in 223Ra+ using high-precision relativistic all-order method where all single and double excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Detailed study of the uncertainty of the parity nonconserving (PNC) amplitude is carried out; additional calculations are performed to estimate some of the missing correlation corrections. A systematic study of the parity conserving atomic properties, including the calculation of the energies, transition matrix elements, lifetimes, hyperfine constants, quadrupole moments of the 6d states, as well as dipole and quadrupole ground state polarizabilities, is carried out. The results are compared with other theoretical calculations and available experimental values.

physics.atom-ph↗

arXiv2008

Polarizabilities of the Mg$^+$ and Si$^{3+}$ ions

A polarization analysis of the fine-structure intervals for the $n = 17$ Rydberg states of Mg and the $n = 29$ states of Si$^{2+}$ is performed. The coefficients of all terms in the polarization expansion up to $r^{-8}$ were computed using a semi-empirical single electron analysis combined with the relativistic all-order single-double method (MBPT-SD) which includes all single-double excitations from the Dirac-Fock wave functions to all orders of perturbation theory. The revised analysis yields dipole polarizabilities of $α_1 = 35.04(3)$ a.u. for Mg$^+$ and $α_1 = 7.433(25)$ a.u. for Si$^{3+}$, values only marginally larger than those obtained in a previous analysis (E. L. Snow and S. R. Lundeen (2007) Phys. Rev. A {\bf 75} 062512, {\em ibid} (2008) {\bf 77} 052501). The polarizabilities are used to make estimates of the multiplet strength for the resonant transition for both ions. The revised analysis did see significant changes in the slopes of the polarization plots. The dipole polarizabilities from the MBPT-SD calculation, namely 35.05(12) a.u. and 7.419(16) a.u., are within 0.3% of the revised experimental values.

physics.atom-ph↗

arXiv2008

Electric Quadrupole Moments of Metastable States of Ca+, Sr+, and Ba+

Electric quadrupole moments of the metastable nd3/2 and nd5/2 states of Ca+, Sr+, and Ba+ are calculated using the relativistic all-order method including all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function to provide recommended values for the cases where no experimental data are available. The contributions of all non-linear single and double terms are also calculated for the case of Ca+ for comparison of our approach with the CCSD(T) results. The third-order many body perturbation theory is used to evaluate contributions of high partial waves and the Breit interaction. The remaining omitted correlation corrections are estimated as well. Extensive study of the uncertainty of our calculations is carried out to establish accuracy of our recommended values to be 0.5% - 1% depending on the particular ion. Comprehensive comparison of our results with other theoretical values and experiment is carried out. Our result for the quadrupole moment of the 3d5/2 state of Ca+ ion, 1.849(17)ea_0^2, is in agreement with the most precise recent measurement 1.83(1)ea_0^2 by Roos et al. [Nature 443, 316 (2006)].

physics.atom-ph↗

arXiv2008

Theoretical study of lifetimes and polarizabilities in Ba+

The 6s-np_j (n=6-9) electric-dipole matrix elements and 6s-nd_j (n=5-7) electric-quadrupole matrix elements in Ba+ are calculated using the relativistic all-order method. The resulting values are used to evaluate ground state dipole and quadrupole polarizabilities. In addition, the electric-dipole 6p_j-5d_j' matrix elements and magnetic-dipole 5d_{5/2}-5d_{3/2} matrix element are calculated using the same method in order to determine the lifetimes of the 6p_{1/2}, 6p_{3/2}, 5d_{3/2}, and 5d_{5/2} levels. The accuracy of the 6s-5d_j matrix elements is investigated in detail in order to estimate the uncertainties in the quadrupole polarizability and 5d_j lifetime values. The lifetimes of the 5d states in Ba+ are extremely long making precise experiments very difficult. Our final results for dipole and quadrupole ground state polarizabilities are alpha_{E1} = 124.15 a^3_0 and alpha_{E2} = 4182(34) a^5_0, respectively. The resulting lifetime values are tau(6p_{1/2})=7.83 ns, tau(6p_{3/2})=6.27 ns, tau(5d_{3/2})=81.5(1.2) s, and tau(5d_{5/2})=30.3(4) s. The extensive comparison with other theoretical and experimental values is carried out for both lifetimes and polarizabilities.

physics.atom-ph↗