flyingphysicist @flyingphysicist@qoto.org

The total energy and other bound state properties of the ground (bound) $1^{1}S$-state in the Ps$^{-}$ (or $e^{-}e^{+}e^{-}$) ion are determined to very high accuracy. Our best variational energy for the ground state in this ion equals $E$ = -0.26200507023298010777040211998 $a.u.$, which is the lowest variational energy ever obtained for this ion. By using our highly wave functions we evaluated (to very high accuracy) a number of different expectation values (or properties) of the Ps$^{-}$ ion which have never been determined in earlier studies. This includes a number of $\langle r^{k}_{ij} \rangle$ expectation values (where $5 \le k \le 11$), all independent quasi-singular Vinty-type expectation values $\langle \frac{{\bf r}_{ij} {\bf r}_{jk}}{r^{3}_{ij}} \rangle$, the two truly singular $\langle \frac{1}{r^{3}_{ij}} \rangle$ expectation values, etc. Our highly accurate expectation values of the electron-positron delta-function of the Ps$^{-}$ ion we have evaluated (to very high accuracy) the rates of two-, three-, four- and five-photon annihilation. We also discuss thermal sources of the fast positrons and annihilation $γ$-quanta located in our Galaxy.

Recently, systems with strong coupling between electronic and vibrational degrees of freedom attract a great attention. In this work, we consider the transient dynamics of the system consisting of strongly coupled vibron and exciton driven by external monochromatic field. We show that under coherent pumping, polarization of exciton exhibits complex quantum dynamics which can be divided into three stages. At the first stage, exciton oscillations at its eigenfrequency relax due to the transition to set of shifted Fock states of vibrons. We demonstrate that these shifted Fock states play the role of an effective reservoir for the excited exciton state. The time of relaxation to this reservoir depends on exciton-vibron coupling. At the second stage, excitation, transferred to the reservoir of the vibronic shifted states at the first stage, returns into electronic degrees of freedom and revival of oscillations at exciton eigenfrequency appears. Thus, the dynamics of molecular polarization exhibit collapses and revivals. At the final stage, these collapses and revivals dissipate and polarization exhibits Rayleigh response at the frequency of the external field. Discovered collapses and revivals manifest in radiation spectrum as multiple splitting of the spectral line near the exciton transition frequency.

A novel strategy for extracting axial (AV) and toroidal (TV) vortices in the magnetically-induced current density (MICD) in molecular systems is introduced, and its pilot application to LiH molecule is demonstrated. It exploits differences in the topologies of AV and TV cores and involves two key steps: selecting a scalar function that can describe vortex cores in MICD and its subsequent topological analysis. The scalar function of choice is $Ω^{B_α}$ based on the velocity-gradient $Ω$ method known in research on classical flows. The Topological Data Analysis (TDA) is then used to analyze the $Ω^{B_α}$ scalar field. In particular, TDA robustly assigns distinct topological features of this field to different vortex types in LiH: AV to saddle-maximum separatrices which connect maxima to 2-saddles located on the domain's boundary, TV to a 1-cycle of the super-level sets of the input data. Both are extracted as the most \emph{persistent} features of the topologically-simplified $Ω^{B_α}$ scalar field.

We address the fundamental question whether or not it is possible to achieve conditions under which the coupling of a single dipole to a strongly confined electromagnetic vacuum can result in non-perturbative corrections to the dipole's ground state. To do so we consider two simplified, but otherwise rather generic cavity QED setups, which allow us to derive analytic expressions for the total ground state energy and to distinguish explicitly between purely electrostatic and genuine vacuum-induced contributions. Importantly, this derivation takes the full electromagnetic spectrum into account while avoiding any ambiguities arising from an ad-hoc mode truncation. Our findings show that while the effect of confinement per se is not enough to result in substantial vacuum-induced corrections, the presence of high-impedance modes, such as plasmons or engineered LC resonances, can drastically increase these effects. Therefore, we conclude that with appropriately designed experiments it is at least in principle possible to access a regime where light-matter interactions become non-perturbative.