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The analytic Born–Oppenheimer (B-O) potential curve for the ground state $X^1\Sigma^+$ of the molecule (H,D,T)Cl is constructed for the whole range of internuclear distances $R \in [0,\infty)$ with an accuracy of 3–5 significant figures in comparison with the Rydberg–Klein–Rees-style potential curve derived from available experimental data on vibrational energies. With an accuracy of 3–4 significant figures, energy predictions are made for HCl (DCl, TCl) for the 836 (1625, 2366) B-O rovibrational bound states with maximal vibrational number $\nu_{\textrm {max}}\,=\,20 (29, 35)$ and maximal angular momentum $L_{\textrm {max}}\,=\,64 (90, 109)$, including 24 (46, 63) weakly-bound states (close to the dissociation limit) with energies ${\lesssim} 10^{-4}$ Hartree. The insufficiency of existing experimental data is indicated, and predictions for the bulk of the missing rovibrational states are made for all HCl, DCl, and TCl molecules.

In this paper, we study the influence of quantum fluctuations (QFs) on the macroscopic quantum tunneling and self-trapping (ST) of a two-component Bose–Einstein condensate in a double-well trap. QFs are described by the Lee–Huang–Yang (LHY) term in the modified Gross–Pitaevskii (GP) equation. Employing the modified GP equation in a scalar approximation, we derive a dimer model using a two-mode approximation. The frequencies of Josephson oscillations and ST conditions under QFs are found analytically and proven by numerical simulations of the modified GP equation. The tunneling and localization phenomena are also investigated for the case of the LHY fluid loaded in a double-well potential.

We present simulation results of the ground state structure and dynamics of quantum droplets (QDs) in one-dimensional spin–orbit coupled binary Bose–Einstein condensates. We have considered two cases for this analysis, such as (i) the mean-field term has a vanishingly small contribution utilizing the equal and opposite inter- and intraspecies interactions and (ii) unequal inter- and intraspecies interactions. The QD exhibits remarkably different natures in each case. In the former case, it exhibits a bright sech-like droplet nature, while in the latter case, we find the flattened sech-like shape of the droplet. Further, we analyze the effect of velocity perturbation on the dynamics in both cases. For the first case, we find a systematic change from the solitonic droplet nature to the breathing droplet, which finally has a moving droplet feature upon increasing the velocity. However, the second case shows similar dynamics except having more dynamically stable features than the first. Finally, we present various dynamics that ensued in the QD due to the quenching of the interaction parameters, coupling parameters or allowing the droplet to undergo collisions.

Periodic asymmetric lattices, viewed from one side to the other, have different spatial potential energies. This difference affects the electronic structure of valence electrons. Our work shows that pronounced even harmonic signals are observed from periodic asymmetric lattices driven by a multi-cycle pulse field. The phases of the odd and even harmonics driven by parallel and anti-parallel laser polarization directions are compared and show different dependences on laser polarization direction. Moreover, it is found that each burst in the synthesized attosecond pulse trains in a periodic asymmetric lattice shows the same carrier-envelope phase. We also show that the even-order harmonic efficiency in periodic asymmetric lattices can be enhanced (reduced) by using a multi-cycle driving laser in the presence of a weak terahertz pulse field.

High-order harmonic generation (HHG) in disordered condensed matter is receiving increasing attention. Meanwhile, the mechanisms of numerous ultrafast phenomena remain unknown. On the one hand, the random variables increase the difficulty of modeling and calculations. On the other hand, the complexity introduced by the disorder severely restricts the analysis of electron dynamics and underlying mechanisms. Here we establish an analytical model on the lattice representation (or the Wannier basis) in the valance and conduction bands. The original and explicit form to describe interband transitions is obtained in periodic crystals. By introducing the disorder-to-periodicity decomposition (DPD) picture, this method can be extended to certain random and disordered lattices. The DPD approximation supported by the numerical result suggests a disorder-uncorrelation perspective for the ultrafast electron dynamics driven by the laser field.

We report the experimental implementation of dynamical decoupling on a small, non-interacting ensemble of up to 25 optically trapped, neutral Cs atoms. The qubit consists of the two magnetic-insensitive Cs clock states $\vert F = 3, m_F = 0\rangle$ and $\vert F = 4, m_F = 0\rangle$, which are coupled by microwave radiation. We observe a significant enhancement of the coherence time when employing Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling. A CPMG sequence with ten refocusing pulses increases the coherence time of 16.2(9) ms by more than one order of magnitude to 178(2) ms. In addition, we make use of the filter function formalism and utilise the CPMG sequence to measure the background noise floor affecting the qubit coherence, finding a power-law noise spectrum $1/\omega^\alpha$ with $\mathit{\alpha} = 0.89(2)$. This finding is in very good agreement with an independent measurement of the noise in the intensity of the trapping laser. Moreover, the measured coherence evolutions also exhibit signatures of low-frequency noise originating at distinct frequencies. Our findings point toward noise spectroscopy of engineered atomic baths through single-atom dynamical decoupling in a system of individual Cs impurities immersed in an ultracold ⁸⁷Rb bath.