arXiv subjects

B. K. Sahoo

Publications and source records attributed to B. K. Sahoo.

At least 91 records · Page 5Linked to original sources

arXiv2018

Comprehensive Study of Properties of a Endohedrally Confined Ca Atom using Relativistic Many-body Methods

We have carried out theoretical investigations of electron correlation effects on the atomic properties of the Ca atom trapped inside an attractive spherically symmetric potential well of an endohedral fullerene C$_{60}$ cluster. Relativistic coupled-cluster (RCC) theory has been employed to obtain electron correlation energy, ionization potential and dipole polarizability of this atom. We have also performed calculations using the Dirac-Hartree-Fock (DF), relativistic second-order many-body perturbation theory (RMBPT(2) method) and relativistic random phase approximation (RRPA) to demonstrate propagation of the correlation effects in these properties. Our results are compared with the reported calculations employing multi-configuration Hartree-Fock (MCHF) method in Phys. Rev. A {\bf 87}, 013409 (2016). We found trends in correlation energy with respect to the potential depth are same, but magnitudes are very large in the relativistic calculations. We have also determined the differential and total cross-sections for elastic scattering of electrons from the free and confined Ca atoms using the electronic charge densities from the Dirac-Hartree core-potential (DFCP) and RCC methods to demonstrate role of potential depth in these properties.

physics.atom-ph↗

arXiv2018

Dipole Polarizability Calculation of Cd Atom: Inconsistency with experiment

Three earlier relativistic coupled-cluster (RCC) calculations of dipole polarizability ($α_d$) of the Cd atom are not in good agreement with the available experimental value of $49.65(1.65) \ e a_0^3$. Among these two are finite-field approaches in which the relativistic effects have been included approximately, while the other calculation uses a four component perturbed RCC method. However, another work adopting an approach similar to the latter perturbed RCC method gives a result very close to that of experiment. The major difference between these two perturbed RCC approaches lies in their implementation. To resolve this ambiguity, we have developed and employed the relativistic normal coupled-cluster (RNCC) theory to evaluate the $α_d$ value of Cd. The distinct features of the RNCC method are that the expression for the expectation value in this approach terminates naturally and that it satisfies the Hellmann-Feynman theorem. In addition, we determine this quantity in the finite-field approach in the framework of A four-component relativistic coupled-cluster theory. Considering the results from both these approaches, we arrive at a reliable value of $α_d=46.02(50) \ e a_0^3$. We also demonstrate that the contribution from the triples excitations in this atom is significant.

physics.atom-ph↗

arXiv2018

Dynamics of Resonant energy transfer in one-dimensional chain of Rydberg atoms

We study resonant energy transfer in a one-dimensional chain of two to five atoms by analyzing time-dependent probabilities as function of their interatomic distances. The dynamics of the system are first investigated by including the nearest-neighbour interactions and then accounting for all next-neighbour interactions. We find that inclusion of nearest-neighbour interactions in the Hamiltonian for three atoms chain exhibits perdiocity during the energy transfer dynamics, however this behavior displays aperiodicity with the all-neighbour interactions. It shows for the equidistant chains of four and five atoms the peaks are always irregular but regular peaks are retrieved when the inner atoms are placed closer than the atoms at both the ends. In this arrangement, the energy transfer swings between the atoms at both ends with very low probability of finding an atom at the center. This phenomenon resembles with quantum notion of Newton's cradle. We also find out the maximum distance up to which energy could be transferred within the typical lifetimes of the Rydberg states.

physics.atom-ph↗

arXiv2018

Higher-component quadrupole polarizabilities: Estimations for the clock states of the alkaline earth-metal ions

Derivations for the higher tensor components of the quadrupole polarizabilities are given and their values for the metastable states of the Ca$^+$, Sr$^+$ and Ba$^+$ alkaline earth-metal ions are estimated. We also give the scalar quadrupole polarizabilities of the ground and metastable states of these ions to compare our results with the previously available theoretical and experimental results. Reasonably good agreement between our calculations with the previous values of scalar quadrupole polarizabilities demonstrate their correctness. The reported scalar and tensor quadrupole polarizabilities could be very useful to estimate the uncertainties due to the gradient of the electric fields in the clock frequencies of the above alkaline earth-metal ions when accuracies of these frequency measurements attain below 10$^{-19}$ precision level.

physics.atom-ph↗

arXiv2018

Studies of the Electric Dipole Polarizability of $^{129}$Xe using the Relativistic Coupled Cluster and the Normal Coupled Cluster Methods

$^{129}$Xe is an important candidate for the searches of electric dipole moments due to violations of time-reversal and parity violations in diamagnetic atoms. In view of the similarities between the electric dipole moment and the polarizability from the point of view of many-body theory, we have performed rigorous calculations of the ground state polarizability of $^{129}$Xe using a self consistent relativistic coupled-cluster method and the relativistic normal coupled-cluster method. The discrepancy between the results from these two methods is two percent, but each of them differs from the accurate measurement of the polarizability of the ground state of $^{129}$Xe by one percent. Our results clearly suggest that the two theoretical methods, we have employed in this work, can be applied in the future to capture electron correlation effects in the electric dipole moment of $^{129}$Xe to a high degree of accuracy.

physics.atom-ph↗

arXiv2018

Relativistic coupled-cluster theory analysis of energies, hyperfine structure constants, and dipole polarizabilities of Cd$^{+}$

Roles of electron correlation effects in the determination of attachment energies, magnetic dipole hyperfine structure constants and electric dipole (E1) matrix elements of the low-lying states in the singly charged cadmium ion (Cd$^+$) have been analyzed. We employ the singles and doubles approximated relativistic coupled-cluster (RCC) method to calculate these properties. Intermediate results from the Dirac-Hartree-Fock approximation, second-order many-body perturbation theory and considering only the linear terms of the RCC method are given to demonstrate propagation of electron correlation effects in this ion. Contributions from important RCC terms are also given to highlight importance of various correlation effects in the evaluation of these properties. At the end, we also determine E1 polarizabilities ($α^{E1}$) of the ground and $5p \ ^2P_{1/2;3/2}$ states of Cd$^+$ in the {\it ab initio} approach. We estimate them again by replacing some of the E1 matrix elements and energies from the measurements to reduce their uncertainties so that they can be used in the high precision experiments of this ion.

physics.atom-ph↗

arXiv2018

Selective highly charged ions as the prospective optical clock candidates with quality factors larger than $10^{15}$

We propose here a few selective highly charged ions (HCIs), namely Ni$^{12+}$ and Cu$^{13+}$, Pd$^{12+}$ and Ag$^{13+}$, that not only promise to be very high accurate optical clocks below $10^{-19}$ uncertainties, but also offer quality factors larger than $10^{15}$ and yet possess simple atomic structures for the experimental set-up. Moreover, these ions have strong optical magnetic-dipole (M1) transitions than the previously proposed HCI clocks. They can be used for the cooling and detection techniques. To demonstrate the projected fractional uncertainties below $10^{-19}$ level, we have estimated the typical orders of magnitudes due to many of the conventional systematics manifested in an atomic clock experiment, such as Zeeman, Stark, black-body radiation, and electric quadrupole shifts, by performing calculations of the relevant atomic properties.

physics.atom-ph↗

arXiv2018

Relativistic Normal Coupled-Cluster Theory for Accurate Determination of Electric Dipole Moments of Atoms: First application to $^{199}$Hg atom

Recent relativistic coupled-cluster (RCC) calculations of electric dipole moments (EDMs) of diamagnetic atoms due to parity and time-reversal violating (P,T-odd) interactions, that are essential ingredients for probing new physics beyond the standard model of particle interactions, differ substantially from the previous theoretical results. It is therefore necessary to perform an independent test of the validity of these results. In view of this, the normal coupled-cluster (NCC) method has been extended to the relativistic regime to calculate the EDMs of atoms by simultaneously incorporating the electrostatic and P,T-odd interactions in order to overcome the shortcomings of the ordinary RCC method. This new relativistic method has been applied to $^{199}$Hg, which currently has a lower EDM limit than that of any other system. The results of our relativistic NCC and self-consistent RCC calculations of the EDM of this atom are found to be close. The discrepancies between these two results on the one hand and those of previous calculations on the other are elucidated. Furthermore, the electric dipole polarizability of this atom, which has computational similarities with the EDM, is evaluated and it is in very good agreement with its measured value.

physics.atom-ph↗

arXiv2017

Relativistic coupled-cluster analysis of parity nonconserving amplitudes and related properties of the $6s ~ ^2S_{1/2} - 5d ~ ^2D_{3/2;5/2}$ transitions in $^{133}$Cs

We present the results of our calculations of the parity nonconserving electric dipole amplitudes ($E1_{PNC}$) for the $6s ~ ^2S_{1/2} - 5d ~ ^2D_{3/2;5/2}$ transitions of $^{133}$Cs employing a relativistic coupled-cluster (RCC) method. $E1_{PNC}$ values for the nuclear spin independent (NSI) and nuclear spin dependent (NSD) parity non-conservation (PNC) effects for different hyperfine levels of the $6s ~ ^2S_{1/2} - 5d ~ ^2D_{3/2}$ transition and only due to the NSD PNC interaction Hamiltonian for all possible hyperfine levels of the $6s ~ ^2S_{1/2} - 5d ~ ^2D_{5/2}$ transition are given. We have also performed calculations of several properties that are relevant for assessing the reliability of the calculations of the amplitudes of the above mentioned transitions. We highlight the importance of correlation effects by giving the results of both the Dirac-Fock (DF) and RCC contributions. Approximate contributions to these properties from the Breit and quantum electrodynamics (QED) interactions have also been evaluated. Plausible experimental schemes to measure these transition amplitudes by light shift techniques and interference involving induced Stark shifts are outlined.

physics.atom-ph↗

arXiv2017

The role of relativistic many-body theory in probing new physics beyond the standard model via the electric dipole moments of diamagnetic atoms

The observation of electric dipole moments (EDMs) in atomic systems due to parity and time-reversal violating (P,T-odd) interactions can probe new physics beyond the standard model and also provide insights into the matter-antimatter asymmetry in the Universe. The EDMs of open-shell atomic systems are sensitive to the electron EDM and the P,T-odd scalar-pseudoscalar (S-PS) semi-leptonic interaction, but the dominant contributions to the EDMs of diamagnetic atoms come from the hadronic and tensor-pseudotensor (T-PT) semi-leptonic interactions. Several diamagnetic atoms like $^{129}$Xe, $^{171}$Yb, $^{199}$Hg, $^{223}$Rn, and $^{225}$Ra are candidates for the experimental search for the possible existence of EDMs, and among these $^{199}$Hg has yielded the lowest limit till date. The T or CP violating coupling constants of the aforementioned interactions can be extracted from these measurements by combining with atomic and nuclear calculations. In this work, we report the calculations of the EDMs of the above atoms by including both the electromagnetic and P,T-odd violating interactions simultaneously. These calculations are performed by employing relativistic many-body methods based on the random phase approximation (RPA) and the singles and doubles coupled-cluster (CCSD) method starting with the Dirac-Hartree-Fock (DHF) wave function in both cases. The differences in the results from both the methods shed light on the importance of the non-core-polarization electron correlation effects that are accounted for by the CCSD method. We also determine electric dipole polarizabilities of these atoms, which have computational similarities with EDMs and compare them with the available experimental and other theoretical results to assess the accuracy of our calculations.

physics.atom-ph↗

arXiv2017

Diverse Trends of Electron Correlation Effects for Properties with Different Radial and Angular Factors in an Atomic System: A case study in Ca$^{+}$

Atomic properties such as field shift constants, magnetic dipole and electric quadrupole hyperfine structure constants, Landé $g_J$ factors, and electric quadrupole moments that are described by electronic operators with different ranks and radial behaviors are studied and the role of electron correlation effects in their determination are investigated. We have adopted the Dirac-Hartree-Fock method, the second- and third-order relativistic many-body perturbation theories, and an all-order relativistic many-body method in the coupled-cluster theory framework considering only the linearized terms and also all the non-linearized terms in the singles and doubles with partial triples excitations approximation to carry out these analyses. Variations in the propagation of electron correlation effects with operators having same angular factors but different radial behaviors and with different ranks are highlighted. Corrections from the higher-order relativistic corrections due to the Breit and quantum electrodynamics interactions to all these properties are also estimated. Understanding of trends of electron correlation effects in these properties can be useful to establish accuracies in the theoretical results of different atomic properties and to substantiate validity of an approximated many-body method.

physics.atom-ph↗

arXiv2017

Static and dynamic polarizabilities of Yb-ion]{Accurate determination of black-body radiation shift, magic and tune-out wavelengths for the $\rm 6S_{1/2} \rightarrow 5D_{3/2}$ clock transition in Yb$^+$

We present precise values of the dipole polarizabilities ($α$) of the ground $\rm [4f^{14}6s] ~ ^2S_{1/2}$ and metastable $\rm [4f^{14} 5d] ~ ^2D_{3/2}$ states of Yb$^+$, that are %vital {\bf important} in reducing systematics in the clock frequency of the $\rm[4f^{14}6s] ~ ^2S_{1/2} \rightarrow [4f^{14}5d] ~ ^2D_{3/2}$ transition. The static values of $α$ for the ground and $\rm [4f^{14} 5d] ~ ^2D_{3/2}$ states are estimated to be $9.8(1) \times 10^{-40} \,\,\rm Jm^2V^{-2}$ and $17.6(5) \times 10^{-40}\,\, \rm Jm^2V^{-2}$, respectively, while the tensor contribution to the $\rm [4f^{14} 5d] ~ ^2D_{3/2}$ state as $- 12.3(3) \times 10^{-40}\,\, \rm Jm^2V^{-2}$ compared to the experimental value $-13.6(2.2) \times 10^{-40}\,\,\rm Jm^2V^{-2}$. This corresponds to the differential scalar polarizability value of the above transition as $-7.8$(5)$\,\times\, 10^{-40}\,\rm Jm^2 V^{-2}$ in contrast to the available experimental value $-6.9$(1.4)$\,\times\, 10^{-40}$\,\, $\rm Jm^2V^{-2}$. This results in the black-body radiation (BBR) shift of the clock transition as $-0.44(3)$ Hz at the room temperature, which is large as compared to the previously estimated values. Using the dynamic $α$ values, we report the tune-out and magic wavelengths that could be of interest to subdue %major systematics due to the Stark shifts and for constructing lattice optical clock using Yb$^+$.

physics.atom-ph↗

arXiv2017

Estimation of BBR shift due to Stark effect for the Microwave $^{113}$Cd$^{+}$ Ion Clock

The microwave clock frequency of the $|5s~^2S_{1/2}, F=0,m_F=0 \rangle \leftrightarrow |5s~^2S_{1/2}, F=1,m_F=0 \rangle$ transition in the $^{113}$Cd$^+$ ion has been reported as 15199862855.0192(10) Hz [Opt. Lett. {\bf 40}, 4249 (2015)]. Fractional systematic due to the black-body radiation (BBR) shift ($β$) arising from the Stark effect in the above clock transition was used as $-1.1 \times 10^{-16}$ from our unpublished preliminary estimation. We present here a precise value as $β=-1.815(77) \times 10^{-16}$ by carrying out rigorous calculations of third-order polarizabilities of the hyperfine levels associated with the clock transition. This is determined by evaluating matrix elements of the magnetic dipole hyperfine interaction Hamiltonian, electric dipole operator and energies between many low-lying states of $^{113}$Cd$^+$. We employ all-order relativistic many-body theories in the frameworks of Fock-space coupled-cluster and relativistic multi-configuration Dirac-Fock methods.

physics.atom-ph↗

arXiv2017

Application of Relativistic Coupled-cluster Theory to Electron Impact Excitations of Mg$^+$ in the Plasma Environment

A relativistic coupled-cluster (RCC) theory is implemented to study electron impact excitations of atomic species. As a test case, the electron impact excitations of the $3s ~ ^2S_{1/2} - 3p ~ ^2P_{1/2;3/2}$ resonance transitions are investigated in the singly charged magnesium (Mg$^+$) ion using this theory. Accuracies of wave functions of Mg$^+$ are justified by evaluating its attachment energies of the relevant states and compared with the experimental values. The continuum wave function of the projectile electron are obtained by solving Dirac equations assuming distortion potential as static potential of the ground state of Mg$^+$. Comparison of the calculated electron impact excitation differential and total cross-sections with the available measurements are found to be in very good agreements at various incident electron energies. Further, calculations are carried out in the plasma environment in the Debye Hückel model framework, which could be useful in the astrophysics. Influence of plasma strength on the cross-sections as well as linear polarization of the photon emission in the $3p ~ ^2P_{3/2} - 3s ~ ^2S_{1/2}$ transition is investigated for different incident electron energies.

physics.atom-ph↗

arXiv2017

Quantum phases of constrained dipolar bosons in coupled one-dimensional optical lattices

We investigate a system of two- and three-body constrained dipolar bosons in a pair of one-dimensional optical lattices coupled to each other by the non-local dipole-dipole interactions. Assuming attractive dipole-dipole interactions, we obtain the ground state phase diagram of the system by employing the cluster mean-field theory. The competition between the repulsive on-site and attractive nearest-neighbor interactions between the chains yields three kinds of superfluids; namely the trimer superfluid, pair superfluid and the usual single particle superfluid along with the insulating Mott phase at the commensurate density. Besides, we also realize simultaneous existence of Mott insulator and superfluid phases for the two- and three-body constrained bosons, respectively. We also analyze the stability of these quantum phases in the presence of a harmonic trap potential.

cond-mat.quant-gas↗

arXiv2017

Relativistic coupled-cluster theory analysis of unusually large correlation effects in the determination of $g_j$ factors in Ca$^+$

We investigate roles of electron correlation effects in the determination of the $g_j$ factors of the $4s ~ ^2S_{1/2}$, $4p ~ ^2P_{1/2}$, $4p ~ ^2P_{3/2}$, $3d ~ ^2D_{3/2}$, and $3d ~ ^2D_{5/2}$ states, representing to different parities and angular momenta, of the Ca$^+$ ion. Correlation contributions are highlighted with respect to the mean-field values evaluated using the Dirac-Hartree-Fock method, relativistic second order many-body theory, and relativistic coupled-cluster (RCC) theory with the singles and doubles approximation considering only the linear terms and also accounting for all the non-linear terms. This shows that it is difficult to achieve reasonably accurate results employing an approximated perturbative approach. We also find that contributions through the non-linear terms and higher-level excitations such as triple excitations, estimated perturbatively in the RCC method, are found to be crucial to attain precise values of the $g_j$ factors in the considered states of Ca$^+$ ion.

physics.atom-ph↗

arXiv2017

Significance of distinct electron correlation effects in determining the P,T-odd electric dipole moment of $^{171}$Yb

Parity and time-reversal violating electric dipole moment (EDM) of $^{171}$Yb is calculated accounting for the electron correlation effects over the Dirac-Hartree-Fock (DHF) method in the relativistic Rayleigh-Schrödinger many-body perturbation theory, with the second (MBPT(2) method) and third order (MBPT(3) method) approximations, and two variants of all-order relativistic many-body approaches, in the random phase approximation (RPA) and coupled-cluster (CC) method with singles and doubles (CCSD method) framework. We consider electron-nucleus tensor-pseudotensor (T-PT) and nuclear Schiff moment (NSM) interactions as the predominant sources that induce EDM in a diamagnetic atomic system. Our results from the CCSD method to EDM ($d_a$) of $^{171}$Yb due to the T-PT and NSM interactions are found to be $d_a = 4.85(6) \times 10^{-20} \langle σ\rangle C_T \ |e| \ cm$ and $d_a=2.89(4) \times 10^{-17} {S/(|e|\ fm^3)}$, respectively, where $C_T$ is the T-PT coupling constant and $S$ is the NSM. These values differ significantly from the earlier calculations. The reason for the same has been attributed to large correlation effects arising through non-RPA type of interactions among the electrons in this atom that are observed by analyzing the differences in the RPA and CCSD results. This has been further scrutinized from the MBPT(2) and MBPT(3) results and their roles have been demonstrated explicitly.

physics.atom-ph↗

arXiv2017

Annexing magic and tune-out wavelengths to the clock transitions of the alkaline-earth metal ions

We present additional magic wavelengths ($λ_{\rm{magic}}$) for the clock transitions in the alkaline-earth metal ions considering circular polarized light aside from our previously reported values in [J. Kaur et al., Phys. Rev. A {\bf 92}, 031402(R) (2015)] for the linearly polarized light. Contributions from the vector component to the dynamic dipole polarizabilities ($α_d(ω)$) of the atomic states associated with the clock transitions play major roles in the evaluation of these $λ_{\rm{magic}}$, hence facilitating in choosing circular polarization of lasers in the experiments. Moreover, the actual clock transitions in these ions are carried out among the hyperfine levels. The $λ_{\rm{magic}}$ values in these hyperfine transitions are estimated and found to be different from $λ_{\rm{magic}}$ for the atomic transitions due to different contributions coming from the vector and tensor part of $α_d(ω)$. Importantly, we also present $λ_{\rm{magic}}$ values that depend only on the scalar component of $α_d(ω)$ for their uses in a specially designed trap geometry for these ions so that they can be used unambiguously among any hyperfine levels of the atomic states of the clock transitions. We also present $α_d(ω)$ values explicitly at the 1064 nm for the atomic states associated with the clock transitions which may be useful for creating "high-field seeking" traps for the above ions using the Nd:YAG laser. The tune out wavelengths at which the states would be free from the Stark shifts are also presented. Accurate values of the electric dipole matrix elements required for these studies are given and trends of electron correlation effects in determining them are also highlighted.

physics.atom-ph↗