We report results for the computation of relativistic effects in quantum many-body systems using quantum annealers. An average accuracy of 98.9% in the fine-structure splitting of boron-like ions with respect to experiments is achieved using the Quantum Annealer Eigensolver (QAE) algorithm on the D-Wave Advantage 5000-qubit hardware, which is substantially higher than that attained on a gate-based quantum device to date. We obtain these results in the framework of the many-electron Dirac theory. We implement QAE using a hybrid quantum annealing method that includes an alternative qubit encoding scheme and decomposing the problem into smaller ones based on perturbation theory.

Magnetic dipole transitions of oxygen molecules, which span the microwave-to-infrared region, play a crucial role in remote sensing applications. However, accurately determining the parameters of these weak transitions has long been a challenge. In this work, we present a saturated absorption spectroscopy measurement of magnetic dipole transitions of ${}^{16}\mathrm{O}_2$ near 764 nm using a comb-locked cavity ring-down spectrometer. The Line positions of eight transitions in the P branch of the $b{}^1{\mathrm{\Sigma }}_g^{+}\leftarrow X{}^3{\mathrm{\Sigma }}_g^{-}(0,0)$ band were determined with an accuracy of better than 3.5 kHz under zero magnetic field, an improvement of two orders of magnitude over previous studies. Zeeman splittings induced by the Earth's geomagnetic field were partially resolved, and their influence on the spectral line profile was meticulously analyzed using the Stokes matrix formalism. The results of this study also indicate the potential for the experimental determination of the Landé $g$ factors of the energies of ${\mathrm{O}}_2$ with better accuracy.

The photoelectron momentum distribution (PMD) for the linear (in intensity) process of one-photon single ionization of carbon monoxide is examined in the polarization plane for several orientations of the linear polarization vector with respect to the molecular axis. For a pulse bandwidth broader than the energy gap between the highest occupied molecular orbital (HOMO) and HOMO-1, the PMD is found to be mixed with HOMO and HOMO-1 signatures because electrons are emitted from these initial orbitals. We show that the asymmetry of the HOMO is strongly revealed in the PMD for any molecular orientation. The backward-forward asymmetry in the PMD and the normalized asymmetry are used as probes of the degree of mixing.

We present analytical and numerical results on the collective excitation spectrum of quasi-one-dimensional spin-orbit (SO)-coupled spin-1 spinor ferromagnetic Bose-Einstein condensates. The collective excitation spectrum, using Bogoliubov–de Gennes theory, reveals the existence of a diverse range of phases in the SO-coupling and Rabi coupling $\left(k_L\text{−}\mathrm{\Omega }\right)$ planes. Based on the nature of the eigenvalue of the excitation spectrum, we categorize the $k_L\text{−}\mathrm{\Omega }$ plane into three distinct regions, namely, I, II (IIa and IIb), and III. In region I, a stable mode with phononlike excitations is observed. In region IIa, single- and multiple-band instabilities are noted with a gapped mode, while multiband instability accompanied by a mode corresponding to no gap between low-lying and first-excited states is realized in region IIb, which also provides evidence of unstable avoided crossing between low-lying and first-excited modes, responsible for the $I_o$ type of oscillatory nonequilibrium dynamical pattern formation. The gap between low-lying and first-excited states increases upon increasing the Rabi coupling and decreases upon increasing the SO coupling. Using eigenvector analysis, we confirm the presence of the spin-dipole mode in the spinlike modes in region II. We corroborate the nature of the collective excitation through real-time dynamical evolution of the ground state perturbed with the quench of the trap using the mean-field Gross-Pitaevskii model. This analysis suggests the presence of dynamical instability leading to the disappearance of the zeroth component of the condensate. In region III, mainly encompassing $\mathrm{\Omega }\sim 0$ and finite $k_L$, we observe phononlike excitations in both the first-excited and the low-lying state. The eigenvectors in this region reveal alternative in- and out-of-phase behaviors of the spin components. Numerical analysis reveals the presence of a superstripe phase for small Rabi coupling in this region, wherein the eigenvector indicates the presence of more complicated spinlike-density mixed modes.

We investigate channeling oscillations in the contrast of a density grating formed by exposing a sample of ultracold atoms to an optical standing-wave pulse. We show that these dynamics can be imprinted on the echo signal associated with a two-pulse atom interferometer. Experimental results are supported by a simple model, which describes the grating contrast as the combination of two separate physical effects, namely, matter-wave interference and classical optical channeling resulting in Pendellösung-like oscillations. We discuss the enhancement in signal strength of echo interferometers that can be achieved by relying on these oscillations.

We introduce a class of one-dimensional complex optical potentials that feature a nonlinearity-induced stability restoration, i.e., the existence of stable nonlinear modes propagating in a waveguide whose linear eigenmodes are unstable. The optical potential is an even function of the transverse coordinate, i.e., the system is parity symmetric but not parity-time symmetric. The stability restoration occurs for asymmetric stationary nonlinear modes that do not respect the parity symmetry. Stable nonlinear states exist either for focusing and defocusing nonlinearities. On the qualitative level the stability restoration can be analyzed using a simple bimodal system. Its solutions enable systematic construction of stable stationary modes and more complex patterns with intensity periodically oscillating along the propagation distance.

We show that, in the framework of quantum circuit electrodynamics in the Heisenberg picture, a finite-length transmission line can be described as a two-port lumped element of Thévenin type. Each port consists of a resistor connected in series to a controlled voltage source. The resistance of the resistors is equal to the characteristic impedance of the line. The controlled voltage sources are governed by linear equations with delay that take into account the reflections at the line ends. We apply this model to a transmission line capacitively coupled to two lumped circuits and obtain the reduced system of Heisenberg equations that governs them. Then, we show these equations can be reformulated as a pair of quantum Langevin-like equations that are coupled through the controlled voltage sources. Finally, we apply our approach to an analytically solvable network. This approach may be useful for the modeling of quantum links between superconducting circuits.

We theoretically consider an ensemble of quantum dimers placed inside an optical cavity. We predict two effects. First, an exchange of angular momentum between the dimers mediated by the emission and reabsorption of the cavity photons leads to the alignment of dimers. Second, the optical angular momentum of the vacuum state of the chiral cavity is transferred to the ensemble of dimers, which leads to the synchronous rotation of the dimers at certain levels of light-matter coupling strength.

The study of phase transitions in dissipative quantum systems based on the Liouvillian is often hindered by the difficulty of constructing a time-local master equation when the system-environment coupling is strong. To address this issue, the complex discretization approximation for the environment is proposed to study the quantum phase transition in the extended Jaynes-Cumming model with an infinite number of boson modes. This approach yields a non-Hermitian effective Hamiltonian that can be used to simulate the dynamics of the spin. It is found that the ground state of this effective Hamiltonian determines the spin dynamics in the single-excitation subspace. Depending on the opening of the energy gap and the maximum population of excitations on the spin degree of freedom, three distinct phases can be identified: fast decaying, localized, and stretched dynamics of the spin. This approach can be extended to multiple excitations, and similar dynamics were found in the double-excitation subspace, indicating the robustness of the single-excitation phase.

We propose $i\text{SWAP-type}$ quantum gates based on geometric phases purely associated with paths on the Schmidt sphere [Phys. Rev. A 62, 022109 (2000)]. These geometric Schmidt gates can entangle qubit pairs to an arbitrary degree; in particular, they can create maximally entangled states from product states by an appropriate choice of base point on the Schmidt sphere. We identify Hamiltonians that generate pure paths on the Schmidt sphere by reverse engineering and demonstrate explicitly that the resulting Hamiltonians can be implemented in systems of transmon qubits. The geometric Schmidt gates are characterized by vanishing dynamical phases and are complementary to geometric single-qubit gates that take place on the Bloch sphere.

Experimental $M_4$ and $M_5$ cross-section curves of some sixth-period elements were observed to exhibit an abnormal crossover above 20 keV, when the $M_5$ binding energy is taken from the most commonly used databases available in the literature for the assessment of absorption effects [Aguilar, Castellano, Segui, Trincavelli, and Carreras, J. Anal. At. Spectrom. 38, 751 (2023)]. This clearly suggests the need for a revision of the published binding-energy values [Bearden and Burr, Rev. Mod. Phys. 39, 125 (1967); Larkins, At. Data Nucl. Data Tables 20, 311 (1977)]. The self-absorption effects of the $M\beta$ line and of bremsstrahlung in an energy region close to the $M_5$ binding energy were analyzed by using energy and wavelength dispersive spectroscopy, respectively. An important inconsistency in the x-ray absorption was found when assessed accordingly with the literature, which led to shift the $M_5$-edge positions of Re, Os, Ir, and Pt. In the particular case of rhenium, theoretical calculations have been performed to assess $M$ binding energies. To this end, the many-electron Dirac equation was numerically solved to estimate the configuration energies associated with $M_5$ one-vacancy states. The binding energies obtained are consistent with the present experimental results, and with the most widely accepted characteristic-energy values.

Dissociative electron attachment (DEA) is one of the processes that shows a strong coupling between the nuclear and electronic degrees of freedom in a molecule. This coupling results in an efficient transformation of the kinetic energy of attaching free electrons into the chemical energy of the compound molecule. A recent discovery of quantum coherence in this process has opened a different dimension in its description. On the other hand, the mass variation in isotopes of the constituent atoms has a profound effect on DEA. In quantum coherence observed in DEA, the isotope effect depicts itself in terms of change in the phase and the amplitude of the interfering dissociation paths. Here, we report the quantum coherence observed in DEA to HD, an isotopolog of ${\mathrm{H}}_2$. In this isotopolog, both ${\mathrm{H}}^{-}$ and ${\mathrm{D}}^{-}$ show identical forward-backward asymmetry in the angular distribution. We explain these findings using the interference between two quantum paths, with the permanent dipole moment due to asymmetric mass playing no role in the process.

The ${}^{229}\mathrm{Th}$ nucleus has a long-lived isomeric state $A^{*}$ at 8.338(24) eV [Kraemer et al., Nature (London) 617, 706 (2023)]. This state is connected to the ground state by an M1 transition. For a hydrogen-like Th ion in the $1s$ state the hyperfine structure splitting is about 0.7 eV. This means that the hyperfine interaction can mix the nuclear ground state with the isomeric state with a mixing coefficient $\beta$ of about 0.03. If the electron is suddenly removed from this system, the nucleus will be left in the mixed state. The probability to find the nucleus in the isomeric state $A^{*}$ is equal to ${\beta }^2\sim {10}^{-3}$. For the $2s$ state the effect is roughly 2 orders of magnitude smaller. An atom with a hole in the $1s$ or $2s$ shell is similar to the hydrogen-like atom, only the hole has a short lifetime $\tau$. After the hole is filled, there is a nonzero probability to find the nucleus in the $A^{*}$ state. Estimates of this probability are presented along with a discussion of possible experiments on Th-doped xenotime-type orthophosphate crystals and other broad band-gap materials.

The problem of orbital collapse of the $5g$ and $6f$ electrons in atoms of superheavy elements (SHEs) is considered. Previously, the presence of the orbital collapse was established for the $4f$ and $5f$ elements of the periodic table. Because of the large centrifugal term for the $f$ and $g$ electrons, the effective radial potential has two wells, one narrow and deep and the other wide but shallow. Depending on the external parameters, the electron can be localized in either the outer well with low binding energy and large average radius or the inner well with higher energy and smaller radius. In this paper, we demonstrate the existence of the orbital collapse for the $5g$ electrons when changing the total angular momentum $J$ of the atom. We also find that for some SHEs two different solutions of the same Dirac-Fock equations may coexist, with the $5g$ electron localized in either the inner or outer well. In both cases, the radial wave functions are nodeless. The problem of the dual-state coexistence is studied by the configuration-interaction method in the Dirac-Fock-Sturm orbital basis as well.

Bimolecular reactions involving small diatomic molecules constitute a fundamental category of chemical processes. Recent experimental breakthroughs have enabled precise timing of the ultrafast formation dynamics of ${\mathrm{D}}_3{}^{+}$ originating from the ${\mathrm{D}}_2\text{−}{\mathrm{D}}_2$ dimer. In this paper, we systematically survey diverse theoretical approaches for numerically simulating bimolecular reaction dynamics, considering various initial geometric configurations of the dimer. Our findings demonstrate the consistency and reliability of both classical and quantum methods in predicting the reaction timescale for ${\mathrm{D}}_3{}^{+}$ formation. Additionally, we illustrate the intricate microscopic details of bimolecular reactions, laying the foundation for comprehending intermolecular interactions.

Conventional mode converters are usually based on wave-number matching in the propagation direction. This often requires applying the periodic modulation in the longitudinal orientation. Here, we propose to construct an efficient supermode converter with only transverse modulation. By linearly changing the surface conductivity of $J_x$ graphene waveguide arrays, we build a synthetic $J_x$ lattice with linearly varying on-site potential in the modal dimension. It turns out that each supermode can fully transfer to its corresponding symmetric partner. The conversion distance of supermodes is inversely proportional to the ramp of linear modulation. In this way, tunable supermode converters can be readily implemented by modulating the surface conductivity of graphene sheets. This study may find promising applications in developing mode converters and mode-division multiplexers utilizing plasmonic waveguide arrays.

The versatility of optical parametric amplifiers makes them excellent sources for ultrashort visible and infrared pulses that drive strong-field physics experiments. We extend four-wave optical parametric amplification to the strong-field regime, known as Kerr instability amplification, and experimentally verify the modified noncollinear conditions for optimum amplification. We confirm that Kerr instability amplification can be used to amplify spectra that span nearly an octave in a single beam. We also amplify the near-infrared portion of the spectrum to generate the third harmonic downstream.

Quantum dots embedded in annular bullseye microcavities have been reported to be efficient single-photon sources. However, the proposed structures thus far often involve gratings of fixed periodicities, which may not be optimal considering the fact that Bessel functions are nonperiodic. In this paper, we present an optimization scheme for chirped annular microcavities where Purcell factors larger than 80 can be achieved through astute selection of the optimization function.

The search for strategies to harness the temperature of quantum systems is one of the main goals of quantum thermodynamics. Here we study the dynamics of a system made of a pair of quantum harmonic oscillators, represented by single-mode cavity fields, interacting with a thermally excited beam of phaseonium atoms, which act as ancillas. The two cavities are arranged in a cascade configuration, so that the second cavity interacts with phaseonium atoms only after their interaction with the first one. We provide exact closed dynamics of the first cavity for arbitrarily long interaction times. We highlight the role played by the characteristic coherence phase of phaseonium atoms in determining the steady states of the cavity fields as well as that of the ancillas. Also, we show how the second cavity follows a non-Markovian evolution due to interactions with the “used” ancillary atoms, which enable information exchange with the first cavity. Adjusting the parameters of the phaseonium atoms, we can determine the final stable temperature reached by the cavities. In this way, the cavities can be heated up as well as cooled down. These results provide useful insights into the use of different types of ancillas for thermodynamic cycles in cavity QED scenarios.