We present the energy and angular distributions of electron emission from a ${\mathrm{CH}}_4$ molecule in collisions with fast bare C ions with energies 3.5 and 5.5 MeV/u. The absolute double differential cross sections (DDCS) are measured for the ejected electrons having energies from 11 eV to 330 eV for $3.5-\mathrm{MeV}/\mathrm{u}$ projectiles and from 5 eV to 330 eV for 5.5 MeV/u bare C ions. The emission is measured in the angular range from ${20}^{\circ }$ to ${160}^{\circ }$. The forward-backward angular asymmetry, the single differential cross sections (SDCS), and the total cross section are deduced from the measured DDCS values. The energy and angular distributions of the DDCS and SDCS are compared with those calculated using a theoretical model based on the prior form of the continuum distorted wave–eikonal initial state (CDW-EIS) approximation. The dynamics of the process is considered within the CDW-EIS approximation, while the initial orbitals of the molecular target are represented using the complete neglect of the differential overlap approximation. The calculations are found to be in very good agreement with the measured cross sections. The angle dependence of the carbon K-LL Auger emission and the total Auger emission cross section are also derived for both projectile energies.

We present both a theoretical and experimental study of the magneto-optical spectra induced with intensity-modulated resonant laser light that synchronously pumps and detects the metastable ${}^4\mathrm{He}$ atoms in the presence of a quasistatic magnetic field. We extend previous work and derive complete analytical expressions for the resonance signals by taking into account arbitrary magnetic-field directions and arbitrary light polarizations. The analytical results are derived by solving the Liouville equation using the irreducible tensor formalism on the assumption of low light power. We discuss the potential application of the derived analytical results in constructing and optimizing a dead-zone-free all-optical atomic magnetometer.

An important step for photonic quantum technologies is the demonstration of a quantum advantage through boson sampling. In order to prevent classical simulability of boson sampling, the photons need to be almost perfectly identical and almost without losses. These two requirements are connected through spectral filtering: improving one leads to a decrease of the other. A proven method of generating single photons is spontaneous parametric down-conversion (SPDC). We explore the fundamental limits of several important SPDC sources and show that an optimal tradeoff between indistinguishability and losses can always be found. We conclude that a 50-photon scattershot boson-sampling experiment using SPDC sources is possible from a computational complexity point of view. To this end, we numerically optimize SPDC sources under the regime of weak pumping and with a single spatial mode.

We study coherent perfect absorption (CPA) theoretically based on a weakly coupled atom-cavity system with an optically pumped second-order nonlinear crystal (SOC) embedded in the cavity. Our system does not require a strong coupling, which is often needed for CPA in previous studies but is challenging to implement experimentally in some systems. The role of the SOC is to introduce a tunable effective decay rate of the cavity, which can lead to CPA in the weak-coupling regime. The proposed system exhibits bistable behaviors, with bistable patterns switchable between conventional and unconventional shapes. By varying the properties of the SOC, the operation point of CPA can be tuned to be inside or outside the bistable regime. It can also be located at the upper or the lower stable branch or even the unstable branch of the bistable hysteresis loop. It is however robust against the parameters of the SOC for any fixed effective decay rate. Our system can potentially be applied to realize optical devices such as optical switches in the weakly coupled regime.

Recently a type of robust exceptional point was found that is insensitive to the coupling disorder in the bulk. Here we show that a disparity emerges when the number of coupled optical cavities in this one-dimensional array changes from even to odd. The robust exceptional point only exists in the former case, whereas in the latter the required coupling for the exceptional point depends inversely on the size of the cavity array and is subjected to coupling disorder in the bulk. We further show that the exceptional points in these two cases are second and third order, respectively. We elucidate the origin of the robust EP as a restricted bulk zero mode, which shares the same robustness against coupling disorder and has a finite amplitude adjacent to the boundary. This finding enables us to identify robust EPs in higher-dimensional systems reliably, which can exist in the presence of either sublattice symmetry or the non-Hermitian particle-hole symmetry evolved from it.

The electron-beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) was employed for the measurement and detailed analysis of the $\delta \lambda ({}^{124}\mathrm{Xe},{}^{136}\mathrm{Xe})$ isotopic shifts of the Al-like $3s^{2}3p{}^{2}P_{1/2}-3s^{2}3p{}^{2}P_{3/2}$, Al-like $3s^{2}3p{}^{2}P_{1/2}-3s^{2}3d{}^{2}D_{3/2}$, Mg-like $3s^2{}^{1}S_0-3s3p{}^{1}P_1$, Mg-like $3s^2{}^{1}S_0-3s3p{}^{3}P_1$, Na-like $3s{}^{2}S_{1/2}-3p{}^{2}P_{1/2}$ ($D_1$), and Na-like $3s{}^{2}S_{1/2}-3p{}^{2}P_{3/2}$ ($D_2$) transitions. Systematic analysis revealed possible line blends and contributing experimental uncertainties. Highly accurate atomic-structure calculations were conducted and used to determine the $\delta {〈r^2〉}^{136,124}$ difference in the mean-square nuclear charge radii of the two xenon isotopes. In the present work, $\delta {〈r^2〉}^{136,124}$ of 0.276 $\pm$ 0.030 ${\mathrm{fm}}^2$ was obtained from the weighted average of the Na-like $D_1$, Mg-like $3s^2-3s3p$ and Al-like $3s^{2}3p-3s^{2}3p$ and $3s^{2}3p-3s^{2}3d$ transitions. This result confirms the value previously determined from the Na-like $D_1$ transition of 0.269 $\pm$ 0.042 ${\mathrm{fm}}^2$. The uncertainty of our result is half of that of previous results for the same isotopes obtained from x-ray spectroscopy of muonic atoms, laser spectroscopy of neutral xenon atoms, and a global evaluation of charge radii. Our result is slightly outside the uncertainty of the value obtained from a King plot analysis of comparable precision. The present work illustrates that extreme-ultraviolet spectroscopy of highly charged ions is a viable approach for measurements of charge nuclear radii differences and can be used to benchmark conventional methods.

Double photoelectron emission from He atoms by intense laser pulses with a wavelength of 394.5 nm is computed for intensities of $3.5–9.2\times {10}^{14}\text{W}/{\text{cm}}^2$. Joint momentum distributions confirm the characteristics seen in classical trajectory calculations. The pronounced transition from back-to-back to side-by-side emission with increasing intensity, the ${\text{He}}^{2+}/{\text{He}}^{+}$ ratios, and a modulation of joint energy spectra agree well with a recent experiment [K. Henrichs et al., Phys. Rev. A 98, 043405 (2018)] if one admits an increase in experimental intensities by a factor of $\sim 2$. We find that Freeman resonances enhance back-to-back emission, we identify the signature of electron repulsion in joint angular distributions, and we interpret the modulation of joint energy spectra as a signature of multiple recollisions.

Phase engineering techniques are used to control the dynamics of long-bosonic Josephson-junction arrays built by linearly coupling Bose-Einstein condensates. Just at the middle point of the underlying discrete energy band of the system, unlocked-relative-phase states are shown to be stationary along with the locked-relative-phase Bloch waves. In finite, experimentally feasible systems, such states find ranges of dynamical stability that depend on the ratio of coupling to interaction energy. The same ratio determines different decay regimes, which include the recurrence of staggered-soliton trains in the condensates around Josephson loop currents at the junctions. These transient solitons are also found in their stationary configurations, which provide striped-density states by means of either dark-soliton or bright-soliton trains. The parametric connection between the latter solitonic states and unlocked-relative-phase states is shown. Additionally, the preparation of maximally out-of-phase (or splay) states is demonstrated to evolve into an oscillation of the uniform density of the condensates that keeps constant the total density of the system and is robust against noise at low coupling.

We propose an experimental protocol to realize discrete-variable quantum teleportation using optomechanical devices. The photonic polarization superposition state of a single photon is teleported to a phononic superposition of two micromechanical oscillators by means of photon-phonon entanglement generation and optical Bell state measurement using two-photon interference. Verification of the protocol is performed by coherent state transfer between the mechanical devices and light. Simulations show the feasibility of the proposed scheme at millikelvin temperatures using state-of-the-art gigahertz optomechanical devices.

Extreme-ultraviolet (EUV) spectra of ${\mathrm{Sn}}^{13+}-{\mathrm{Sn}}^{15+}$ ions have been measured in an electron-beam ion trap (EBIT). A matrix inversion method is employed to unravel convoluted spectra from a mixture of charge states typically present in an EBIT. The method is benchmarked against the spectral features of resonance transitions in ${\mathrm{Sn}}^{13+}$ and ${\mathrm{Sn}}^{14+}$ ions. Three new EUV lines in ${\mathrm{Sn}}^{14+}$ confirm its previously established level structure. This ion is relevant for EUV nanolithography plasma but no detailed experimental data currently exist. We used the Cowan code for first line identifications and assignments in ${\mathrm{Sn}}^{15+}$. The collisional-radiative modeling capabilities of the Flexible Atomic Code were used to include line intensities in the identification process. Using the 20 lines identified, we have established 17 level energies of the $4p^{4}4d$ configuration as well as the fine-structure splitting of the $4p^5$ ground-state configuration. Moreover, we provide state-of-the-art ab initio level structure calculations of ${\mathrm{Sn}}^{15+}$ using the configuration-interaction many-body perturbation code ambit. We find that the here-dominant emission features from the ${\mathrm{Sn}}^{15+}$ ion lie in the narrow 2% bandwidth around 13.5 nm that is relevant for plasma light sources for state-of-the-art nanolithography.

We study the dynamical response of the Dirac vacuum state to a very strong time-dependent electric field pulse, whose frequency is chirped in time. The resulting field-induced electron-positron pair-creation process can be used to examine various proposals for time-dependent frequency spectra of the external field. It turns out that the Dirac vacuum can be used as sensitive probe that can respond to the instantaneous values of the frequency at each moment of time by producing electrons with a characteristic energy. This almost instantaneous response feature of the vacuum state permits us to introduce a generalized rate equation. It is based on the concept of a time-dependent decay rate and can provide semianalytical solutions to predict the number of created electron-positron pairs during the interaction with arbitrarily chirped electric field pulses.

Feshbach resonances play a major role in translationally cold-molecule preparation. In this context, their laser control is of crucial importance. This work is devoted to the depiction of some basic mechanisms of such a control using intense, short laser pulses and referring to nonlinear multiphoton processes. Our goal is to adiabatically transport a Feshbach resonance onto a zero-width resonance, the characteristics of which have already been discussed in the literature. Three processes are then addressed: (i) during the rise of the pulse and its plateau, the preparation of a so-called laser bound molecule (LBM) still stable, but structurally different from the standard chemically bound molecule; (ii) during the pulse switching off, an adiabatic transport of this LBM on a very few excited vibrational levels, and (iii) concomitantly, a filtration strategy to photodissociate all these levels except one, giving thus rise to but a single field-free excited vibrational state. With or without an eventual stimulated Raman adiabatic passage technique to bring all the population to the ground rovibrational state, this opens an alternate for a full optical control of ultracold-molecule formation. The illustrative example, offering the potentiality to be transposed to other diatomics, is ${\mathrm{H}}_2^{+}$.

We theoretically study the static and dynamic behavior of a BEC immersed in a large Fermi sea of ultracold atoms under conditions of tunable interspecies interaction. The degenerate Bose-Fermi mixture is kept in an elongated trap, typical for a single-beam optical dipole trap. We focus on the case of repulsive Bose-Fermi interaction and develop mean-field models to simulate the system over a wide range of repulsion strength. We further get analytical solutions in the regimes of phase separation and weak interaction. We obtain static density profiles and the frequency of the radial breathing mode, which is an elementary dynamic phenomenon of the mixture. Our results unveil the structure of the Bose-Fermi interface and describe the origin of the frequency shift of the breathing mode when the components become phase-separated at strong repulsion. We show that the mediated interaction between bosons induced by the Fermi sea can be understood as an adiabatic second-order mean-field effect, which is valid also beyond the weak-interaction regime for relevant experimental conditions. These results are consistent with our recent observations [Lous et al., Phys. Rev. Lett. 120, 243403 (2018); Huang et al., Phys. Rev. A 99, 041602(R) (2019)] in a mixture of ${}^{41}\mathrm{K}$ and ${}^6\mathrm{Li}$.

We study the contacts, large-momentum tail, radio-frequency spectroscopy, and some other universal relations for an ultracold one-dimensional (1D) two-component Fermi gas with spin-orbit coupling (SOC). Different from previous studies, we find that the $q^{-8}$ tail in the spin-mixing (off-diagonal) terms of the momentum distribution matrix is dependent on the two SOC parameters in the laboratory frame for 1D systems, where $q$ is the relative momentum. This tail can be observed through time-of-flight measurement as a direct manifestation of the SOC effects on the many-body level. Besides the traditional 1D even-wave scattering length, we find that two new physical quantities must be introduced due to the SOC. Consequently, two new adiabatic energy relations with respect to the two SOC parameters are obtained. Furthermore, we derive the pressure relation and virial theorem at short distances for this system. To find how the SOC modifies the large-momentum behavior, we take the SOC parameters as perturbations since the strength of the SOC should be much smaller than the corresponding strength scale of the interatomic interactions. In addition, by using the operator product expansion method, we derive the asymptotic behavior of the large-momentum distribution matrix up to the $q^{-8}$ order and find that the diagonal terms of the distribution matrix include the contact of traditional 1D even-wave scattering length as the leading term and the SOC modified terms beyond the leading term, the off-diagonal term is beyond the subleading term and is corrected by the SOC parameters. We also find that the momentum distribution matrix shows spin-dependent and anisotropic features. Furthermore, we calculate the momentum distribution matrix in the laboratory frame for the experimental implication. In addition, we calculate the high-frequency tail of the radio-frequency spectroscopy and find that the presence of the contact related to the center-of-mass momentum in the radio-frequency spectral is due to the SOC effects. This paper paves the way for exploring the profound properties of many-body quantum systems with SOC in one dimension.

Atomic Kapitza-Dirac Bragg regime scattering is a multiphoton process in which a neutral atom undergoes a change of momentum through an interaction with a coherent light source. When the Bragg conditions are met, the outgoing atom beams are spatially quantized. Counterpropagating lasers act as pump and probe scattering from far-off-resonant excited intermediate electronic states, leaving the atoms in the electronic ground state with quantized transverse momentum. Each nontrivial scattering event imparts transverse velocity and therefore kinetic energy to the deflected atoms through recoil. In the Bragg regime, the loss of energy in the light fields is equal to the gain of kinetic energy in the atom. Energy nonconserving intermediate states, which are described by nonadiabatic contributions, are not accounted for by first-order off-resonant states. By comparing the solutions of increasing orders of off-resonant intermediate states, it becomes clear that calculating the correct Pendellösung frequencies and phases requires including an ever increasing number of off-resonant states in proportion to the square root of the field strength.

We theoretically study binary Bose-Einstein condensates trapped in a single-well harmonic potential to probe the dynamics of collective atomic motion. The idea is to choose tunable scattering lengths through Feshbach resonances such that the ground-state wave function for two types of the condensates are spatially immiscible where one of the condensates, located at the center of the potential trap, can be effectively treated as a potential barrier between bilateral condensates of the second type of atoms. In the case of small wave-function overlap between bilateral condensates, one can parametrize their spatial part of the wave functions in the two-mode approximation together with the time-dependent population imbalance $z$ and the phase difference $\varphi$ between two wave functions. The condensate in the middle can be approximated by a Gaussian wave function with the displacement of the condensate center $\xi$. As driven by the time-dependent displacement of the central condensate, we find the Josephson oscillations of the collective atomic motion between bilateral condensates as well as their anharmonic generalization of macroscopic self-trapping effects. In addition, with the increase in the wave-function overlap of bilateral condensates by properly choosing tunable atomic scattering lengths, the chaotic oscillations are found if the system departs from the state of a fixed point. The Melnikov approach with a homoclinic solution of the derived $z, \varphi$, and $\xi$ equations can successfully justify the existence of chaos. All results are consistent with the numerical solutions of the full time-dependent Gross-Pitaevskii equations.

We study the formation of localized patterns arising in doubly resonant dispersive optical parametric oscillators. They form through the locking of fronts connecting a continuous-wave and a Turing pattern state. This type of localized state can be seen as a slug of the pattern embedded in a homogeneous surrounding. They are organized in terms of a homoclinic snaking bifurcation structure, which is preserved under the modification of the control parameters of the system. We show that, in the presence of phase mismatch, localized patterns can undergo oscillatory instabilities which make them breathe in a complex manner.

After reviewing the pioneering work by Zel'Dovich in which radiation is amplified perpendicular to the axis of a rotating conductor, we consider an alternative scattering arrangement. We demonstrate superradiant amplification of electromagnetic waves with orbital angular momentum directed axially towards a rotating conductor. Taking into account recent advances in optics and condensed-matter systems, our approach presents new possibilities for rotational superradiance experiments. We discuss remaining challenges that must be faced before a laboratory observation of the Zel'Dovich effect can be considered feasible.

Variational quantum algorithms are promising applications of noisy intermediate-scale quantum (NISQ) computers. These algorithms consist of a number of separate prepare-and-measure experiments that estimate terms in a Hamiltonian. The number of terms can become overwhelmingly large for problems at the scale of NISQ hardware that may soon be available. We use unitary partitioning (developed independently by Izmaylov et al. [J. Chem. Theory Comput. 16, 190 (2020)]) to define variational quantum eigensolver procedures in which additional unitary operations are appended to the ansatz preparation to reduce the number of terms. This approach may be scaled to use all coherent resources available after ansatz preparation. We also study the use of asymmetric qubitization to implement the additional coherent operations with lower circuit depth. Using this technique, we find a constant factor speedup for lattice and random Pauli Hamiltonians. For electronic structure Hamiltonians, we prove that linear term reduction with respect to the number of orbitals, which has been previously observed in numerical studies, is always achievable. For systems represented on 10–30 qubits, we find that there is a reduction in the number of terms by approximately an order of magnitude. Applied to the plane-wave dual-basis representation of fermionic Hamiltonians, however, unitary partitioning offers only a constant factor reduction. Finally, we show that noncontextual Hamiltonians may be reduced to effective commuting Hamiltonians using unitary partitioning.