The resonant single, double, triple, and quadruple Auger decays of the core-excited $\mathrm{Ar}2{p_{3/2}}^{-1}4s$ are investigated by using the multistep approaches, i.e., the cascade, knock-out, and shake-off mechanisms within the framework of many-body perturbation theory. The Auger rates, the branching ratios for the different configurations in the final ions and the probabilities of the spectator, participator, and shake processes, as well as the ion yields are obtained. The cascade processes are dominant in the resonant double Auger decay since the initial Rydberg electron $4s$ preferentially remains in its orbital as a spectator in the primary resonant single Auger decay. In the direct processes, the spectator processes are essential for the populations of final states, while the participator processes become dominant as the number of emitted Auger electrons increases, especially for the resonant quadruple Auger decay. Furthermore, the shake processes also affect significantly the final states for the direct processes. The calculated ion yields (in percentages) of ${\mathrm{Ar}}^{+}, {\mathrm{Ar}}^{2+}, {\mathrm{Ar}}^{3+}$, and ${\mathrm{Ar}}^{4+}$ of 65.3, 31.0, 3.6, and 0.09, respectively, are in agreement with the recent experimental values of 69, 28, 3, and 0.03 [Hikosaka et al., Phys. Rev. A 89, 023410 (2014)] and 66, 30, 4, and 0.2 [Samson et al., Phys. Rev. A 54, 2099 (1996)].

An analytical method for calculating the electromagnetic fields of a nonparaxial elegant Laguerre-Gaussian (LG) vortex beam is presented for arbitrary pulse duration, spot size, and LG mode. This perturbative approach provides a numerically tractable model for the calculation of arbitrarily high radial and azimuthal LG modes in the nonparaxial regime, without requiring integral representations of the fields. A key feature of this perturbative model is its use of a Poisson-like frequency spectrum, which allows for the proper description of pulses of arbitrarily short duration. This model is thus appropriate for simulating laser-matter interactions, including those involving short laser pulses.

We study an optomechanical system for the purpose of generating a nonclassical mechanical state when a mechanical oscillator is quadratically coupled to a single-mode cavity field driven by a squeezed optical field. The system corresponds to a regime where the optical dissipation dominates both the mechanical damping and the optomechanical coupling. We identify that multiphonon processes emerge in the optomechanical system and show that a mechanical oscillator prepared in the ground state will evolve into an amplitude-squared squeezed vacuum state. The Wigner distribution of the steady state of the mechanical oscillator is non-Gaussian exhibiting quantum interference and fourfold symmetry. This nonclassical mechanical state, generated via reservoir engineering, can be used for quantum correlation measurements of the position and momentum of the mechanics below the standard quantum limit.

We present a theoretical model for controlling the Fraunhofer diffraction patterns of a weak probe field passing through an atomic vapor. In this model a Rydberg state is taken as the uppermost level. The proposed system contains a combined two well-known $V$- and $\mathrm{\Xi }$-type configurations which are exposed to a weak probe field and two control fields. The position-dependent feature of the atom-field interaction leads to the periodic transmission spectrum, and various Fraunhofer diffraction patterns are obtained due to the all-optical grating. Also, it is shown that the intensity of the higher-order diffraction can be controlled by tuning the coupling field intensity and the interaction length.

We report coherent frequency conversion in the gigahertz range via three-wave mixing in a single artificial atom in open space. All frequencies involved are in the vicinity of transition frequencies of the three-level atom. A cyclic configuration of levels is therefore essential, which we have realized with an artificial atom based on the flux qubit geometry. The atom is continuously driven at two transition frequencies and we directly measure the coherent emission at the sum or difference frequency. Our approach enables coherent conversion of the incoming fields into the coherent emission at a designed frequency in prospective devices of quantum electronics.

Weak values have been shown to be helpful especially when considering them as the outcomes of weak measurements. In this paper we show that, in principle, the real and imaginary parts of the weak value of any operator may be elucidated from expectation values of suitably defined density, flux, and Hermitian commutator operators. Expectation values are the outcomes of strong (projective) measurements, implying that weak values are general properties of operators in association with pre- and postselection and they need not be preferentially associated with weak measurements. They should be considered as an important measurable property which provides added information compared with the “standard” diagonal expectation value of an operator. As the first specific example we consider the determination of the real and imaginary parts of the weak value of the momentum operator employing projective time-of-flight experiments. Then the results are analyzed from the point of view of Bohmian mechanics. Finally, we consider recent neutron interferometry experiments used to determine the weak values of the neutron spin.

Nonlocal advantage of quantum coherence (NAQC) or steerability of local quantum coherence is a strong nonlocal resource based on coherence complementarity relations. In this work, we provide an upper bound on the number of observers who can independently steer the coherence of the observer in the other wing in a scenario where half of an entangled pair of spin-$\frac{1}{2}$ particles is shared between a single observer (Bob) in one wing and several observers (Alices) on the other, who can act sequentially and independently of each other. We consider one-parameter dichotomic POVMs for the Alices and mutually unbiased basis in which Bob measures coherence in the case of the maximally entangled bipartite qubit state. We show that not more than two Alices can exhibit NAQC when the $l_1$ norm of coherence measure is probed, whereas for two other measures of coherence, only one Alice can reveal NAQC within the same framework.

We introduce a method for representing the low-energy subspace of a bosonic field theory on the qubit space of digital quantum computers. This discretization leads to an exponentially precise description of the subspace of the continuous theory thanks to the Nyquist-Shannon sampling theorem. The method makes the implementation of quantum algorithms for purely bosonic systems as well as fermion-boson interacting systems feasible. We present algorithmic circuits for computing the time evolution of these systems. The complexity of the algorithms scales polynomially with the system size. The algorithm is a natural extension of the existing quantum algorithms for simulating fermion systems in quantum chemistry and condensed-matter physics to systems involving bosons and fermion-boson interactions and has a broad variety of potential applications in particle physics, condensed matter, etc. Due to the relatively small amount of additional resources required by the inclusion of bosons in our algorithm, the simulation of electron-phonon and similar systems can be placed in the same near-future reach as the simulation of interacting electron systems. We benchmark our algorithm by implementing it for a two-site Holstein polaron problem on an Atos Quantum Learning Machine quantum simulator. The polaron quantum simulations are in excellent agreement with the results obtained by exact diagonalization.

Quantum coherence is a fundamental aspect of quantum physics and plays a central role in quantum information science. This essential property of the quantum states could be fragile under the influence of the quantum operations. The extent to which quantum coherence is diminished depends both on the channel and the incoherent basis. Motivated by this, we propose a measure of nonclassicality of a quantum channel as the average quantum coherence of the state space after the channel acts on, minimized over all orthonormal basis sets of the state space. Utilizing the squared $l_1$-norm of coherence for the qubit channels, the minimization can be treated analytically and the proposed measure takes a closed form of expression. If we allow the channels to act locally on a maximally entangled state, the quantum correlation is diminished making the states more classical. We show that the extent to which quantum correlation is preserved under local action of the channel cannot exceed the quantumness of the underlying channel. We further apply our measure to the quantum teleportation protocol and show that a nonzero quantumness for the underlying channel provides a necessary condition to overcome the best classical protocols.

We explore the suitability of ultracold collisions between spin-polarized $\mathrm{SrF}\left({}^2\mathrm{\Sigma }^{+}\right)$ molecules and $\mathrm{Rb}\left({}^{2}S\right)$ atoms as elementary steps for the sympathetic cooling of $\mathrm{SrF}\left({}^2\mathrm{\Sigma }^{+}\right)$ molecules in a magnetic trap. To this end, we carry out quantum-mechanical scattering calculations on ultracold Rb + SrF collisions in a magnetic field based on an accurate potential-energy surface for the triplet electronic state of Rb-SrF developed ab initio using a spin-restricted coupled cluster method with single, double, and noniterative triple excitations [RCCSD(T)]. The Rb-SrF interaction has a global minimum with a well depth of 3444 ${\mathrm{cm}}^{-1}$ in a bent geometry and a shallow local minimum in the linear geometry. Despite such a strong and anisotropic interaction, we find that converged close-coupling scattering calculations on Rb + SrF collisions in a magnetic field are still possible using rotational basis sets including up to 125 closed rotational channels in the total angular momentum representation. Our calculations show that electronic spin relaxation in fully spin-polarized Rb-SrF collisions occurs much more slowly than elastic scattering over a wide range of magnetic fields (1–1000 G) and collision energies (${10}^{-5}–{10}^{-3}$ K), suggesting good prospects of sympathetic cooling into the microkelvin regime of laser-cooled $\mathrm{SrF}\left({}^2\mathrm{\Sigma }^{+}\right)$ molecules with spin-polarized $\mathrm{Rb}\left({}^{2}S\right)$ atoms in a magnetic trap. We show that incoming $p$-wave scattering plays a significant role in ultracold collisions due to the large reduced mass of the Rb-SrF collision pair. The calculated magnetic-field dependence of the inelastic cross sections at $1.4\mu \mathrm{K}$ displays a rich resonance structure including a low-field $p$-wave resonance, which suggests that external magnetic fields can be used to enhance the efficiency of sympathetic cooling in heavy atom-molecule mixtures.

We propose a way to cool the torsional motion of a nanodiamond, which contains a nitrogen-vacancy (NV) center and is levitated by an optical tweezer. Following the rotation of the particle, the NV-center electron spin experiences varying external fields and so leads to spin-torsion coupling. By optically pumping the electrons from a higher energy level to a lower level, the torsional energy is dissipated. We give the analytical result for the damping torque exerted on the nanodiamond and evaluate the final cooling temperature by the fluctuation-dissipation theorem. It is shown that the quantum regime of the torsion can be reached with our scheme.

We demonstrate a momentum-resolved detection technique in a sensitive Bragg atom interferometer, where the populations of the atomic final states are measured by the Raman spectroscopy method. This method avoids cross-couplings due to the space overlapping of atomic states and significantly increases the fringe visibility without requiring spatial separation. Thanks to this detection method, we are able to achieve the high fringe visibility of greater than $80\%$ at an interrogation time of $T=1$ ms. With $T=250$ ms and a visibility of $10\%$, it shows an improved resolution for gravity measurements at the level of $7\times {10}^{-10}g$ in an integration time of 1000 s. This work can be applied in developing compact portable sensing devices or improving the precision of tests on fundamental physics.

We numerically study the characteristics of optical rogue waves (RWs) in midinfrared supercontinuum (MIR-SC) generation with a femtosecond pump in the anomalous dispersion regime of a chalcogenide photonic crystal fiber. An approach based on seed-induced modulation instability is used to regulate the formation of optical RWs. By carrying out multiple simulations in the presence of noise, we show that optical RWs can be generated in a more controlled manner by providing a seed with an optimum modulation frequency. The redshift range of optical RWs is expanded to a considerable extent in the seed-induced case rather than the noise-induced case. Furthermore, the increase of pump power can facilitate the redshift of optical RWs. These results demonstrate how a seed pulse affects the formation of optical RW for MIR-SC generation with a femtosecond pump in the anomalous dispersion regime of fiber, indicating that optical RW can be used to generate ultra-broadband MIR-SC.

We study the tunability of nanofilms composed of linear molecular aggregates for slow- and fast-light performance. In order to describe a wide range of intensity field regimes, we consider a two-exciton model for the molecular aggregate where exciton creation or annihilation may occur. Our simulations show fractional delays and advancements of the order of those found in longer propagating media. This nanometric device presents two functionalities: (i) it allows the existence of slow or fast light in a different bandwidth of pulsed signals and (ii) such dual performance can be tuned by a small perturbation of the input signal amplitude for a fixed pulse temporal width. Both effects are tested under the usual presence of disorder in these molecular systems. This study concludes that a molecular-aggregate nanofilm presents a wide control of group velocity in the GHz and THz bandwidths.

We report theoretical and numerical results on the dynamics of pulsing lasers with gain and absorber sections subject to delayed optical self-feedback. We consider two modeling approaches, with the Yamada model, on the one hand, and a delay model for ring-cavity mode-locked lasers, on the other hand. We focus on the limit where a single mode is involved, and we show that, in the case without feedback, the dynamics of both models show very good quantitative agreement: $Q$-switched periodic pulsing regimes with similar properties are observed. A bifurcation analysis unveils the conditions for the dynamics to be similar in both systems when an additional delayed feedback term is considered: in particular, what is important is to match the period and the width of the pulsing dynamics of the solitary lasers. Our results show that the simple Yamada model can catch the essence of the dynamics of pulsing lasers with feedback in the limit of single-mode systems. This may considerably simplify, in future work, the investigation of the dynamics of certain self-pulsing lasers with feedback.

Recent advances in experimental techniques allow one to create a quantum point contact between two Fermi superfluids in cold atomic gases with a tunable transmission coefficient. In this Rapid Communication we propose that three distinct behaviors of charge transports between two Fermi superfluids can be realized in this single setup, which are the multiple Andreev reflection, the self-trapping, and the Josephson oscillation. We investigate the dynamics of atom number difference between two reservoirs for different initial conditions and different transmission coefficients, and present a coherent picture of how the crossover between different regimes takes place. Our results can now be directly verified in the current experimental system.

Two-photon annihilation of a twisted positron colliding with a plane-wave electron is investigated. Attention is restricted to a beam-and-target scenario consisting of a rapidly moving twisted positron colliding with a slow moving electron, assumed to be in its rest frame. Emphasis is also placed on the case whereby the product $\gamma$ photons are resolved into plane waves. We present analytical and numerical results on how the angular distribution of the photons depends on the opening angle, intrinsic angular momentum state, and the energy of the twisted positron and compare these results to the case of an incident plane-wave positron. Two-photon annihilation with a twisted positron in the low-energy limit is also briefly investigated in which one of the photons is coherently emitted into a twisted Bessel state while the other is resolved into a plane wave. Finally, numerical results are presented on two-photon annihilation with a positron prepared in a superposition of two twisted Bessel states.

The continuous spontaneous localization (CSL) model strives to describe the quantum-to-classical transition from the viewpoint of collapse models. However, its original formulation suffers from a fundamental inconsistency in that it is explicitly energy nonconserving. Fortunately, a dissipative extension to CSL has been recently formulated that solves such an energy-divergence problem. We compare the predictions of the dissipative and nondissipative CSL models when various optomechanical settings are used and contrast such predictions with available experimental data, thus building the corresponding exclusion plots.

The number of bound states in a standard rectangular potential well depends on the potential depth and width. In an impenetrable one-dimensional rectangular potential well, there are infinite bound states. In this work we study a non-Hermitian Riesz-Feller kinetic energy; i.e., the second-order derivative of the standard kinetic energy operator is replaced by a fractional, $\alpha \mathrm{th}$-order derivative. We show that for $\alpha <2$ a particle in an impenetrable one-dimensional rectangular potential well contains a finite number of bound states and an infinite number of metastable decaying states. The transitions from bound states to metastable decaying states occur at $\alpha$ values that correspond to exceptional points, for which two bound states coalesce. Our findings indicate that one can describe a transition of highly excited bound states to metastable decaying states, for example due to the interactions of atoms and molecules with the environment, by using the Riesz-Feller kinetic energy operator rather than the standard one.

We consider open quantum systems with factorized initial states, providing the structure of the reduced system dynamics, in terms of environment cumulants. We show that such completely positive (CP) and trace-preserving (TP) maps can be unraveled by linear stochastic Schrödinger equations (SSEs) characterized by sets of colored stochastic processes (with $n\mathrm{th}$-order cumulants). We obtain both the conditions such that the SSEs provide CPTP dynamics and those for unraveling an open system dynamics. We then focus on Gaussian non-Markovian unravelings, whose known structure displays a functional derivative. We provide a description that replaces the functional derivative with a recursive operatorial structure. Moreover, for the family of quadratic bosonic Hamiltonians, we are able to provide an explicit operatorial dependence for the unraveling.