We show analytically that the collapse and revival in the population dynamics of the atom-cavity coupled system under the rotating wave approximation (RWA), valid only at very weak coupling, is an artifact as the atom-cavity coupling is increased. Even the first-order correction to the RWA is able to bring about the absence of the collapse in the dynamics of atomic population inversion thanks to intrinsic oscillations resulting from the transitions between two levels with the same atomic quantum number. The removal of the collapse is valid for a wide range of coupling strengths which are accessible to current experimental setups. In addition, based on our analytical results that greatly improve upon the conventional RWA, even the strong-coupling power spectrum can now be explained with the help of the numerically exact energy levels.

Besides the two fundamental symmetric and antisymmetric modes, a thin metal slab surrounded by a dielectric medium supports an infinite number of other modes whose propagation distances, however, are extremely short. We show that such a higher-order mode, normally not regarded to be useful, can turn into a long-range surface-plasmon polariton in circumstances where the fundamental long-range mode does not exist and the propagation length of the single-interface surface-plasmon polariton is negligible. This transition, which is an electromagnetic near-field phenomenon not previously observed, occurs with a broad range of bandwidths and materials, especially in the context of high-index semiconductors. The long-range behavior of the higher-order surface-plasmon polaritons does not originate from the coupling between the polaritons supported by the individual boundaries, and in some situations it comes with increased field confinement, which is the opposite of what occurs for the fundamental long-range surface mode. Our results, which follow from rigorous electromagnetic theory, provide deeper insight into the foundations of thin-film plasmonics and suggest avenues for enhanced properties of nanophotonic devices involving modern polaritonic media.

We use an analytical method to study the dissipative dynamics of a two-level system (TLS) under a harmonic driving. The method is based on a combination of the unitary transformation and Born–Markov master-equation approach. Our main aim is to clarify the effects of counter-rotating (CR) terms of both the driving and TLS-bath (dissipative) coupling on the dynamics, in comparison with the rotating-wave results of different schemes, i.e., the well-known traditional rotating-wave approximation method, and two particular methods: one just takes into account the effects of the driving CR terms and the other the effects of the dissipative CR terms, which are derived from our general treatment. Our main results are as follows: (i) by calculating the time-dependent population difference and coherence, in the case of resonant strong driving, we demonstrate that the CR terms of both the driving and dissipative coupling play an important role in the relaxation and dephasing processes, and also the properties of the steady state; (ii) in the case of largely detuned driving, we find that the CR terms of the dissipative coupling become negligible while those of the driving contribute dominant modifications to the time evolution and steady state. Moreover, we examine the influence of the dissipation on coherent destruction of tunneling under a largely detuned strong driving. We show that an almost complete suppression of the tunneling can be achieved for a relatively long time; (iii) under certain conditions, we find numerical equivalence between one of two particular methods and the Floquet–Born–Markov approach based on exact numerical treatment of the Floquet Hamiltonian. It turns out that our method is more simple and efficient than the Floquet–Born–Markov approach for both analytical and numerical calculations. By the general comparison of different treatments we demonstrate the dynamical effects of CR terms of both the driving and the dissipative coupling on the coherence and population difference.

The impact of nonadiabatic laser-induced molecular alignment on filamentation is numerically studied. Weak- and strong-field models of impulsive molecular alignment are compared in the context of nonlinear pulse propagation. It is shown that the widely used weak-field model describing the refractive index modification induced by impulsive molecular alignment accurately reproduces the propagation dynamics providing that only a single pulse is involved during the experiment. On the contrary, it fails at reproducing the nonlinear propagation experienced by an intense laser pulse traveling in the wake of a second strong laser pulse. The discrepancy depends on the relative delay between the two pulses and is maximal for delays corresponding to half the rotational period of the molecule.

We present a quantum master equation describing a Bose-Einstein condensate with particle loss on one lattice site and particle gain on the other lattice site whose mean-field limit is a non-Hermitian $\mathcal{PT}$-symmetric Gross-Pitaevskii equation. It is shown that the characteristic properties of $\mathcal{PT}$-symmetric systems, such as the existence of stationary states and the phase shift of pulses between two lattice sites, are also found in the many-particle system. Visualizing the dynamics on a Bloch sphere allows us to compare the complete dynamics of the master equation with that of the Gross-Pitaevskii equation. We find that even for a relatively small number of particles the dynamics are in excellent agreement and the master equation with balanced gain and loss is indeed an appropriate many-particle description of a $\mathcal{PT}$-symmetric Bose-Einstein condensate.

A definitive determination of the nature of the approach to the critical charge is illustrated for the ${\left(1s^{2}2s3s\right)}^{1,3}S$ and the ${\left(1s^{2}2s3p\right)}^{1,3}P$ states of the Be isoelectronic series. The features that conclusively indicate that the outermost orbital becomes an infinitely diffuse hydrogenlike orbital upon approaching the critical charge $Z_c=3$ are the asymptotic proportionality of the ionization energy to ${(Z-3)}^2$ and the approach of the corresponding quantum defect to an integer which is equal to the number of orbitals of the same symmetry in the atomic core.

Relativistic dipolar to hexadecapolar polarizabilities of the ground state and some excited states of hydrogenic atoms are calculated by using numerically exact energies and wave functions obtained from the Dirac equation with the Lagrange-mesh method. This approach is an approximate variational method taking the form of equations on a grid because of the use of a Gauss quadrature approximation. The partial polarizabilities conserving the absolute value of the quantum number $\kappa$ are also numerically exact with small numbers of mesh points. The ones where $\left|\kappa \right|$ changes are very accurate when using three different meshes for the initial and final wave functions and for the calculation of matrix elements. The polarizabilities of the $n=2$ excited states of hydrogenic atoms are also studied with a separate treatment of the final states that are degenerate at the nonrelativistic approximation. The method provides high accuracies for polarizabilities of a particle in a Yukawa potential and is applied to a hydrogen atom embedded in a Debye plasma.

Experimental cross sections and cross-section ratios reported in the literature for direct double ionization of the outer shells of helium, neon, and argon atoms resulting from bare ions ranging from protons to uranium and for antiprotons are analyzed in terms of a first- and second-order interference model originally proposed by McGuire [J. H. McGuire, Phys. Rev. Lett. 49, 1153 (1982)]. Empirical formulas for the various contributions to double ionization plus information about the phase difference between the first- and second-order mechanisms are extracted from the data. Projectile and target scalings are also extracted. Total cross sections and their ratios determined using these formulas and scalings are shown to be in very good agreement with experimental data for lower-Z projectiles and impact velocities larger than 1 a.u. For very-high-Z projectiles, the amount of double ionization is overestimated, probably due to saturation of probabilities that is not accounted for in scaling formulas.

We theoretically investigate the control of a magnetic Feshbach resonance using a bound-to-bound molecular transition driven by spatially modulated laser light. Due to the spatially periodic coupling between the ground and excited molecular states, there exists a band structure of bound states, which can uniquely be characterized by some extra bumps in radio-frequency spectroscopy. With the increasing of coupling strength, the series of bound states will cross zero energy and directly result in a number of scattering resonances, whose position and width can be conveniently tuned by the coupling strength of the laser light and the applied magnetic field (i.e., the detuning of the ground molecular state). In the presence of the modulated laser light, universal two-body bound states near zero-energy threshold still exist. However, compared with the case without modulation, the regime for such universal states is usually small. A unified formula, which embodies the influence of the modulated coupling on the resonance width is given. The spatially modulated coupling also implies a local spatially varying interaction between atoms. Our work proposes a practical way of optically controlling interatomic interactions with high spatial resolution and negligible atomic loss.

Rydberg states of atomic helium with principal quantum numbers ranging from $n=20$ to $n=100$ have been prepared by non-resonance-enhanced single-color two-photon excitation from the metastable $2{{}^{3}S}_1$ state. Photoexcitation was carried out using linearly and circularly polarized pulsed laser radiation. In the case of excitation with circularly polarized radiation, Rydberg states with azimuthal quantum number $|m_{\ell }|=2$ were prepared in zero electric field and in homogeneous electric fields oriented parallel to the propagation axis of the laser radiation. In sufficiently strong electric fields, individual Rydberg–Stark states were resolved spectroscopically, highlighting the suitability of non-resonance-enhanced multiphoton excitation schemes for the preparation of long-lived high-$|m_{\ell }|$ hydrogenic Rydberg states for deceleration and trapping experiments. Applications of similar schemes for Doppler-free excitation of positronium atoms to Rydberg states are also discussed.

We consider a polarized Fermi gas in the BCS-BEC crossover region above the critical temperature within a T-matrix formalism. By treating the mean-field-like shift of the quasiparticle energies in a self-consistent manner, we avoid the known pathological behavior of the standard Nozières-Schmitt-Rink approach in the polarized case, i.e., the polarization has the right sign and the spin polarizability is positive. The momentum distributions of the correlated system are computed and it is shown that, in the zero-temperature limit, they satisfy the Luttinger theorem. Results for the phase diagram, the spin susceptibility, and the compressibility are discussed.

Time-of-flight images are a common tool in ultracold atomic experiments, employed to determine the quasimomentum distribution of the interacting particles. If one introduces a constant artificial electric field, then the quasimomentum distribution evolves in time as Bloch oscillations are generated in the system and then are damped, showing a complex series of patterns. In different-mass Fermi-Fermi mixtures, these patterns are formed from a frustrated phase separation in momentum space that is driven by Mott physics for large electric fields which stabilize them for long times.

We propose a scheme to investigate the interplay between the Kondo-exchange interaction and the quantum spin Hall effect with ultracold fermionic alkaline-earth-metal atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, although the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling.

We investigate the polarization of odd versus even high-order-harmonic generation (HHG) from oriented asymmetric molecules exposed to a strong and linearly polarized laser field. Our numerical simulations show that the properties of polarization of harmonics at diverse orientation angles differ significantly from each other. In particular, odd and even harmonics show different angle dependences of ellipticity. Our analyses reveal that the interplay of intramolecular interference and the contributions of different HHG routes plays an important role in the ellipticity of odd-even harmonics. In addition, the excited states also have nontrivial influence on this ellipticity. While the minimum arising from two-center interference is not easy to identify in the odd-even HHG spectra of asymmetric molecules, we show that the ellipticity of harmonics can be used as a sensitive tool to probe the position of the minimum, which is important in asymmetric molecular orbital imaging.

We study experimentally and theoretically the response of a superradiant or bad-cavity laser to an applied coherent drive. We observe two forms of synchronization (injection locking) between the superradiant ensemble and the applied drive: one attractive and one repulsive in nature. In the region of repulsion, the atomic spin state that stores laser coherence undergoes three-dimensional dynamics, as opposed to a two-parameter description of the electric field in a traditional good-cavity laser. We derive a phase diagram of predicted behavior and experimentally measure the response of the system across various trajectories therein.

We propose a definition for the efficiency that can be universally applied to all classes of quantum optical detectors. This definition is based on the maximum amount of optical loss that a physically plausible device can experience while still replicating the properties of a given detector. We prove that detector efficiency cannot be increased using linear optical processing. That is, given a set of detectors, as well as arbitrary linear optical elements and ancillary light sources, it is impossible to construct detection devices that would exhibit higher efficiencies than the initial set.

The concept of ponderomotive potential is upgraded to a regime in which radiation friction becomes dominant. The radiation friction manifests itself in long-term capturing of the particles released at the focus and impenetrability of the focus from the exterior. We apply time scale separation to the Landau-Lifshitz equation splitting the particle motion into quivering and slow drift of a guiding center. The drift equation is deduced by averaging over fast motion.

In [Phys. Rev. A 90, 023833 (2014)], we offer a solution to the problem of constructing a scattering potential $v\left(x\right)$ which possesses scattering properties of one's choice at an arbitrarily prescribed wave number. This solution involves expressing $v\left(x\right)$ as the sum of $n\le 6$ finite-range unidirectionally invisible potentials. We improve this result by reducing the upper bound on $n$ from 6 to 4. In particular, we show that we can construct $v\left(x\right)$ as the sum of up to $n=3$ finite-range unidirectionally invisible potentials, unless if it is required to be bidirectionally reflectionless.

We derive a steering inequality based on a fine-grained uncertainty relation to capture Einstein-Podolsky-Rosen steering for bipartite systems. Our steering inequality improves over previous ones since it can experimentally detect all steerable two-qubit Werner state with only two measurement settings on each side. According to our inequality, pure entangled states are maximally steerable. Moreover, by slightly changing the setting, we can express the amount of violation of our inequality as a function of their violation of the Clauser-Horne-Shimony-Holt inequality. Finally, after deriving a monogamy relation we prove that the amount of violation of our steering inequality is, up to a constant factor, a lower bound on the key rate of a one-sided device-independent quantum key distribution protocol secure against individual attacks.