We explore the dynamics of bright solitary waves in one-dimensional spin-tensor-momentum coupled spin-1 Bose-Einstein condensates. Our results show that the solitary waves have nonzero spin and nematicity simultaneously, hence we call them spin-nematic solitary waves. The ground-state solitary waves carry a finite momentum and display the zero-energy modes arising from symmetry breaking. In the motion of the solitary wave, the spin-tensor-momentum coupling induces the flip of the spin-nematic vector on a unit Bloch sphere, which in turn produces a force to result in the oscillatory motion of the solitary wave. The effects of a harmonic trap are also analyzed. These findings reveal the unique properties of solitary waves affected by the spin-tensor-momentum coupling.

In recent times, device-independent certification of quantum states has been one of the intensively studied areas in quantum information. However, all such schemes utilize projective measurements which are practically difficult to generate. In this paper, we consider the one-sided device-independent scenario and propose a self-testing scheme for the two-qubit maximally entangled state using nonprojective measurements, in particular, three three-outcome extremal positive operator-valued measures. We also analyze the robustness of our scheme against white noise.

We perform highly accurate calculations of the leading-order QED correction to the ground electronic state of molecular hydrogen. Numerical results are obtained for a grid of the internuclear distances $R=0–10$ a.u. with the relative precision of about ${10}^{-8}$. The major numerical uncertainty of previous QED results [K. Piszczatowski, G. Łach, M. Przybytek, J. Komasa, K. Pachucki, and B. Jeziorski, J. Chem. Theory Comput. 5, 3039 (2009)] has been eliminated. Nevertheless, the discrepancy with measurements in HD at the level of 1.9 $\sigma$ persists.

Identifying dynamical signatures of excited-state quantum phase transitions (ESQPTs) in experimentally realizable quantum many-body systems is helpful for understanding the dynamical effects of ESQPTs. In such systems, the highly controllable spinor Bose-Einstein condensates (BECs) offer an exceptional platform to study ESQPTs. In this work, we investigate the dynamical characteristics of the ESQPT in spin-1 BEC by means of the Loschmidt echo spectrum. The Loschmidt echo spectrum is an extension of the well-known Loschmidt echo and defined as the overlaps between the evolved state and the excited states of the initial Hamiltonian. We show that both the time-evolved and long-time-averaged Loschmidt echo spectrum undergo a remarkable change as the system passes through the critical point of the ESQPT. Moreover, the particular behavior exhibited by the Loschmidt echo spectrum at the critical point stands as a dynamical detector for probing the ESQPT. We further demonstrate how to capture the features of the ESQPT by using the energy distribution associated with the Loschmidt echo spectrum for time-evolved and long-time-averaged cases, respectively. Our findings contribute to a further verification of the usefulness of the Loschmidt echo spectrum for witnessing various quantum phase transitions in many-body systems and provide a different way to experimentally examine the dynamical consequences of ESQPTs.

Quantum backflow refers to the counterintuitive fact that the probability can flow in the direction opposite to the momentum of a quantum particle. This phenomenon has been seen to be small and fragile for one-dimensional systems, in which the maximal amount of backflow has been found to be bounded. Quantum backflow exhibits dramatically different features in two-dimensional systems that, in contrast to the one-dimensional case, allow for degenerate energy eigenstates. Here we investigate the case of a charged particle that is confined to move on a finite disk punctured at the center and that is pierced through the center, and normally to the disk, by a magnetic flux line. We demonstrate that quantum backflow can be unbounded (in a certain sense), which makes this system a promising physical platform regarding the yet-to-be-performed experimental observation of this fundamental quantum phenomenon.

Multipartite entanglement is an indispensable resource in quantum communication and computation; however, it is a challenging task to faithfully quantify this global property of multipartite quantum systems. In this work we study the concurrence fill, which admits a geometric interpretation to measure genuine tripartite entanglement for the three-qubit system [Xie and Eberly, Phys. Rev. Lett. 127, 040403 (2021)]. First, we use the well-known three-tangle and bipartite concurrence to reformulate this quantifier for all pure states. We then construct an explicit example to conclusively show that the concurrence fill can be increased under local operations and classical communication (LOCC) on average, implying it is not an entanglement monotone. Moreover, we give a simple proof of the LOCC monotonicity of the three-tangle and find that the bipartite concurrence and the squared concurrence can have distinct performances under the same LOCC. Finally, we propose a reliable monotone to quantify genuine tripartite entanglement, which can also be easily generalized to the multipartite system. Our results shed light on the study of genuine entanglement and also reveal the complex structure of multipartite systems.

We analyze the optimal basis for generating the maximum relative entropy of quantum coherence by an arbitrary gate on a two-qubit system. The optimal basis is not unique and the high-quantum-coherence-generating gates are also typically high-entanglement-generating ones and vice versa. However, the profile of the relative frequencies of Haar random unitaries generating different amounts of entanglement for a fixed amount of quantum coherence is different from the one in which the roles of entanglement and quantum coherence are reversed, although both follow a Beta distribution.

Variational quantum algorithms (VQAs) offer a promising path toward using near-term quantum hardware for applications in academic and industrial research. These algorithms aim to find approximate solutions to quantum problems by optimizing a parametrized quantum circuit using a classical optimization algorithm. A successful VQA requires fast and reliable classical optimization algorithms. Understanding and optimizing how off-the-shelf optimization methods perform in this context is important for the future of the field. In this work, we study the performance of four commonly used gradient-free optimization methods [sequential least-squares quadratic programming, constrained optimization by linear approximations, the covariance matrix adaptation evolutionary strategy (CMA-ES), and the simultaneous perturbation stochastic approximation (SPSA)] to find ground-state energies of a range of small chemistry and material science problems. We test a telescoping sampling scheme (where the accuracy of the cost-function estimate provided to the optimizer is increased as the optimization converges) for all methods, demonstrating mixed results across our range of optimizers and problems chosen. We further hyperparameter tune two of the four optimizers (CMA-ES and SPSA) across a large range of models and demonstrate that with appropriate hyperparameter tuning, CMA-ES is competitive with and sometimes outperforms SPSA (which is not observed in the absence of hyperparameter tuning). Finally, we investigate the ability of an optimizer to beat the “sampling-noise floor” given by the sampling noise of each cost-function estimate provided to the optimizer. Our results demonstrate the necessity for tailoring and hyperparameter tuning known optimization techniques for inherently noisy variational quantum algorithms and that the variational landscape that one finds in a VQA is highly problem and system dependent. This provides guidance for future implementations of these algorithms in experiments.

Partial and final projectile charge states are theoretically analyzed after ${\mathrm{Li}}^{+}$ ions frontally collide with a single-layer graphene surface with potassium atoms adsorbed on it, in the very low deposition limit where the adsorbed atoms negligibly interact with each other. We applied a model based on first principles that accounts for all the details of the surface and is used to describe the resonant charge exchange processes occurring in binary collisions between the projectile and the adsorbate, and between the projectile and the C atoms of the graphene surface located in the surroundings of the adsorption site. Completely different neutral fraction dependences with the outgoing velocity are found for the projectiles scattered by the adsorbate and by carbon atoms located far from the adsorbed atom. In addition, an important influence of the adsorbate is perceived in the neutralization of projectiles colliding with the first and second set of carbon atoms nearest to the adsorption site. For C atoms located at middle-range distances (∼6.7 Å), the final charge state of the projectile is not affected by the adsorbate presence, even when an effective interaction between the projectile and the K adsorbed atom is revealed via appreciable projectile level widths.

Accurate calculations of phase lag associated with coherent control where an excited system decays into more than one product channel have recently been reported for atomic barium in Wang and Greene [Y. Wang and C. H. Greene, Phys. Rev. A 105, 013113 (2022)]. The present study extends the calculations to make predictions of that observable for another alkaline-earth-metal atom, strontium, with a discussion of its spectrum and phase lag for energies between the ${\mathrm{Sr}}^{+}4d_{3/2}$ and $4d_{5/2}$ thresholds. We explore the physics influenced by the electron correlations of strontium and the long-range Coulomb potential. The behavior of the phase lag cannot be simply addressed by a time-delay analysis, although the latter is often used to address the prominent channel of resonance decay of doubly excited states.

A recently developed version of the configuration interaction (CI) method for open shells with a large number of valence electrons has been used to study two heavy atoms, californium (Cf, $Z=98$) and einsteinium (Es, $Z=99$). Motivated by experimental work to measure the hyperfine structure (HFS) for these atoms, we perform the calculations of the magnetic dipole HFS constants $A$ and electric quadrupole HFS constant $B$ for the sake of interpretation of the measurements in terms of nuclear magnetic moment $\mu$ and electric quadrupole moment $Q$. For verification of our computations, we have also carried out similar calculations for the lighter homologs dysprosium (Dy, $Z=66$) and holmium (Ho, $Z=67$), whose electronic structures are similar to Cf and Es, respectively. We have conducted a revision of the nuclear moments of some isotopes of Es leading to an improved value of the magnetic moment of ${}^{253}\mathrm{Es} [\mu \left({}^{253}\mathrm{Es}\right)=4.20\left(13\right){\mu }_N]$.

Single and double ionization of berylliumlike ${\mathrm{C}}^{2+}$ by a single photon is investigated in the energy range from 292 to 350 eV in the vicinity of the $K$-shell single-ionization threshold. Energy resolutions range between 160 meV for overview scans and 11 meV for high-resolution spectroscopy. The experimental cross sections include contributions from the $1s^{2}2s^2{}^{1}S$ ground level and the $1s^{2}2s2p{}^{3}P$ metastable levels. A comparison of the experimentally derived cross-section function for photoabsorption by ${\mathrm{C}}^{2+}$ to a model based on previous $R$-matrix calculations shows very satisfying agreement.

We investigated the Rydberg-state excitation process of a hydrogen atom subjected to spatially homogeneous and inhomogeneous laser fields by means of ab initio calculations. It is found that, comparing with atoms exposed to spatially homogeneous laser fields, the excitation probability decreases and the electron tends to occupy the states with lower principal quantum numbers and angular quantum numbers for atoms in spatially inhomogeneous laser pulses. Furthermore, calculations of a quantum model without taking into account ionization of the electron after it is coherently captured by the Rydberg state are inconsistent with the above-stated findings by ab initio calculations. Analysis indicates that the aforementioned intriguing features can be attributed to the enhanced ionization of the Rydberg states by inhomogeneous laser fields since the distributions of Rydberg states of high principal quantum numbers and angular quantum numbers locate far away from the core where the inhomogeneous electric fields become significant.

We study the properties of self-bound liquid droplets of three-dimensional Bose mixtures in a weak random potential with Gaussian correlation function at both zero and finite temperatures. Using the Bogoliubov theory, we derive useful formulas for the ground-state energy, the equilibrium density, the depletion, and the anomalous density of the droplet. The quantum fluctuation induced by the disorder known as the glassy fraction is also systematically computed. At finite temperature, we calculate the free energy, the thermal equilibrium density, and the critical temperature in terms of the disorder parameters. We show that when the strength and the correlation length of the disorder potential exceed a certain critical value, the droplet evaporates and is eventually entirely destroyed. We calculate the density profiles of this exotic state by means of numerical simulations of the corresponding generalized disorder Gross-Pitaevskii equation. Our predictions reveal that as the strength of the disorder gets larger, the atomic density varies rapidly in the plateau region. We point out in addition that the peculiar interplay of the disorder and the repulsive Lee-Huang-Yang corrections play a pivotal role in the collective modes of the self-bound droplet.

Topological pumping connects the topological features of a modulated system with its transport behavior. It provides a powerful means for robust topological transport between distant nodes even in a one-dimensional chain, which may find applications in wave manipulation and quantum information processing. Here, we experimentally demonstrate an adiabatic pumping scheme, topological pumping of a defect state, by introducing a Fock photonic lattice, which is a classical analog of the Fock-state lattice of the two-mode Jaynes-Cummings model. Since this pumping is always protected by an energy gap even for a large-size system, its pumping efficiency can be enhanced considerably compared with the conventional topological pumping schemes. Moreover, a topologically protected beam splitter is also realized by designing the pumping channels of a defect state. The experimental results agree well with theoretical simulations. Our scheme provides a different route to study topological transport and implement novel photonic devices.

We analyze recent approaches to quantum Markovianity and how they relate to the proper definition of quantum memory. We show that the well-known criterion of information backflow does not report a distinction between the quantum or classical character of observed memory effects. Therefore, as a complement to the current description, we propose a definition of a quantum backflow based on the concept of component dynamical maps and convexity arguments. In particular, for a natural choice of component maps, we provide a practical characterization of quantum memory in terms of the new concept of quantum memory witness. In particular, we give a full description of such witnesses in a qubit case. Finally, we discuss a potential generalization of component maps that should capture certain classical features of information backflow.