By numerically solving the time-dependent Schrödinger equation, we theoretically investigated the dynamic interference in multiphoton excitation and ionization of hydrogen irradiated by 400-nm linearly polarized laser pulses. Interference of the multiphoton excitation paths at the rising and falling edges of the laser pulses gives rise to the fast oscillations of the intensity-dependent yield of the excited states. Our results show that the period of the oscillation increases abruptly when the laser intensity increases above the eight-photon ionization threshold. By tracing the population evolution of the ground state, we find that the depletion of the ground state on the rising edge of the laser pulse closes the multiphoton excitation path at the falling edge of the pulse. The slower oscillation comes from the interference of the excitation paths at different instants during the rising edge of the laser pulses. The change in the interference paths in the high-laser-intensity region also occurs in multiphoton ionization. The photoelectrons released at different instants of the rising edge of the laser pulses possess different parities. This difference is imprinted in the up-down asymmetry along the laser polarization direction in the photoelectron momentum distribution. The dynamic interference of the Rydberg states provides rich information about the dynamics in strong-field ionization.

We study the motion of a superfluid vortex in condensates having different background density profiles, ranging from parabolic to uniform. The resulting effective point-vortex model for a generic power-law potential $\propto r^k$ can be experimentally realized with recent advances in optical-trapping techniques. Our analysis encompasses both empty-core and filled-core vortices. In the latter case, the vortex acquires a mass due to the presence of distinguishable atoms located in its core. The axisymmetry allows us to reduce the coupled dynamical equations of motion to a single radial equation with an effective potential $V_{\mathrm{eff}}$. In many cases, $V_{\mathrm{eff}}$ has a single minimum, where the vortex precesses uniformly. The dynamics of the vortex and the localized massive core arises from the dependence of the energy on the radial position of the vortex and from the $r^k$ trap potential. We find that a positive vortex with small mass orbits in the positive direction, but the sense of precession can reverse as the core mass increases. Early experiments and theoretical studies on two-component vortices found some qualitatively similar behavior.

We propose a theoretical scheme for photon blockade in a cavity quantum electrodynamic system consisting of an $N$-type atomic medium interacting with a single-mode Fabry-Pérot cavity. In contrast to inefficient nonlinear-dispersion-induced photon blockade suppressed by a large detuning of atomic transitions, the photon blockade in our scheme is induced by a large nonlinear dissipation of the cavity created by the near-resonant $N$-type atomic system. A deep photon blockade is manifested by a vanishing equal-time second-order correlation function within the cavity linewidth. We also provide an explanation for this dissipation-induced photon blockade. This work provides an efficient photon blockade because it works in the near-resonance case.

The synthetic gauge field and dissipation are of crucial importance in both fundamental physics and applications. Here, we investigate the interplay of the uniform flux and the on-site gain and loss by considering a dissipative two-leg ladder model. By calculating the spectral winding number and the generalized Brillouin zone, we predict the non-Hermitian skin effect, whose skin modes display the bipolar localization. This skin effect emerges when the flux is not an integer multiple of $\pi$. We further demonstrate the breakdown of the chiral currents due to the presence of the skin effect by studying single-particle dynamics. Moreover, we show that the non-Hermiticity can drive a flux-dependent topological transition characterized by a hidden Chern number. Our results provide a scheme to manipulate the non-Hermitian skin effect and topological phase transitions, which may find potential applications in lasing, light manipulating, and signal processing.

We observe experimentally the fractional topological phase (FTP) robustness to the dephasing noise in two-qudit photonic systems. We use a source of photon pairs generated by spontaneous parametric down-conversion, hyperentangled in the polarization and photon path degrees of freedom. The dephasing noise is described theoretically via Kraus maps and experimentally implemented via the spatial light modulator. The FTP is a great candidate to explore in the implementation of quantum processing and communication due to its robustness to dephasing noise.

Many security loopholes exist in quantum key distribution (QKD) due to the imperfections of realistic devices. On the source side, the decoy-state method can defend against the most severe photon-number-splitting (PNS) attack and improve the performance of QKD. Measurement-device-independent QKD and twin-field QKD have further closed all loopholes on the detection side. In this paper, we propose a valuable optical injection-locking loophole for the case when the internal isolator inside the laser is removed. We first introduce the effects of the injection locking with different injection intensities on the source frequency. Through the successive responses of adjacent pulses from frequency ports of the dense wavelength division multiplexer, the decoy state and the signal state can be partially distinguished. The specific injection-locking-loophole analysis of the isolatorless decoy phase-encoding Bennet-Brassard 1984 QKD and decoy phase-matching QKD protocols with external optical injection has been deeply studied. Simulation results show that, if we maintain the same observed gain statistics as normal after an external optical injection locking, the loophole cannot be exploited for a PNS attack when the QKD distance is short. As the QKD distance increases, a PNS attack at a medium distance using the optical injection-locking loophole does not threaten the security; the security is still valid. With the further increase of the QKD distance, the lower-bound secure key rate is higher than the upper-bound secure key rate given by a PNS attack at a long distance, some of the keys must be insecure, and information will be leaked.

Energy can be stored in quantum batteries by electromagnetic fields as chargers. In this paper, the performance of a quantum battery with single and double chargers is studied. It is shown that by using two independent charging fields, prepared in coherent states, the charging power of the quantum battery can be significantly improved, though the average number of embedded photons are kept the same in both scenarios. The results reveal that for the case of initially correlated states of the chargers, the amount of extractable energy, measured by ergotropy, is more than initially uncorrelated ones, with appropriate degrees of field intensity. Though the correlated chargers lead to greater reduction in the purity of the quantum battery, more energy and in turn more ergotropy are stored in this case. In addition, we study the battery-charger mutual information and von Neumann entropy and by using their relation we find that both quantum and classical correlations are generated between the quantum battery and chargers. We also study quantum consonance of the battery as the nonlocal coherence among its cells and find some qualitative relations between the generation of such correlations and the capability of energy storage in the quantum battery.

Ionization of the $3p$ orbital of argon (Ar) monomers, dimers (${\mathrm{Ar}}_2$), and small-size Ar clusters (${\mathrm{Ar}}_n,\langle n\rangle \approx 15$) is investigated for 90-eV electron impact. Experimentally, the three-dimensional momentum vectors of the two outgoing electrons and the residual ion are measured in triple coincidence, as is the mass-over-charge ratio of the ion, using a reaction microscope that covers a large part of the final-state phase space. The triple-differential cross sections (TDCS) are obtained for almost the full solid angle of the ejected electron, in which the data for Ar monomers are well reproduced by $B$-spline $R$-matrix calculations for ejected electron energies of 3 eV, 5 eV, and 10 eV, and projectile scattering angles of ${10}^{\circ }$ and ${20}^{\circ }$. Compared to the Ar monomer, the cross sections for ${\mathrm{Ar}}_2$ and ${\mathrm{Ar}}_n$ exhibit effects due to the neighboring atoms by the suppression of binary and recoil lobes and the enhanced electron emission out of the projectile scattering plane. These environmental effects are further investigated using a multicenter three-distorted-wave theory, which can generate the TDCSs for electron-impact ionization of ${\mathrm{Ar}}_2$. These studies reveal an important role of multicenter scattering reactions on the ionization dynamics of Ar clusters. Moreover, a two-center interference is not found in the TDCS of ${\mathrm{Ar}}_2$. This is interpreted as due to the involvement of orbitals with both gerade and ungerade symmetries in the ionization process.

We study the photoelectron momentum distribution from strong-field tunneling ionization of two molecules with similar highest occupied molecular orbitals, i.e., ${\mathrm{O}}_2$ and ${\mathrm{CO}}_2$. We find that the tiny difference between those two molecular orbitals can be clearly identified from the photoelectron momentum distributions in an elliptically polarized laser field, while it can hardly be identified in a linearly polarized laser field due to the strong Coulomb focusing effect. Furthermore, we show that the momentum distribution in the elliptically polarized laser field can be used to reveal how the molecular orbital affects the ionization time distribution of the photoelectron.

The effect produced by surface defects on grazing-incidence fast atom diffraction (GIFAD) patterns is studied by considering the presence of terraces in a LiF(001) sample. For helium atoms impinging along the $\langle 110\rangle$ direction of the LiF surface, we analyze the influence of a monolayer terrace with its edge oriented parallel or perpendicular to the axial channel. We found that the presence of an outward transverse step introduces a diffuse background above the Laue circle, which displays additional peaked structures. For inward transverse steps, instead, such a background is placed below the Laue circle, showing a much weaker intensity. On the other hand, parallel steps give rise to asymmetric angular distributions, which are completely confined to the Laue circle. Therefore, these theoretical results suggest that GIFAD might be used to characterize terrace defects.

For measurements in near-zero magnetic fields, vector atomic magnetometers are promising alternatives to scalar versions, but generally suffer from inconsistent performance over three axes. We present a single-beam vector magnetometer with three-axis isotropic sensitivity based on ${}^4\mathrm{He}$ atomic alignment. Longitudinal parametric resonance with atoms pumped by linearly polarized light is proposed for the $z$-axis measurement, while the Hanle effect in transverse geometry is used for $x$- and $y$-axis measurements. The evolution of atomic alignment multipole components and expressions of the three-axis magnetic responses are analyzed in detail. We describe the experimental operation of the proposed magnetometer with a magnetic-field noise floor of $150\mathrm{fT}/{\mathrm{Hz}}^{1/2}$ for the three axes, which is attractive for biomagnetism requiring vector characterization and source reconstruction.

We provide an analytical model to fabricate an exponential localization of a Bose-Einstein condensate under a bichromatic optical lattice. Such localization is famously known as Anderson localization. The degree of localization is investigated using the participation ratio to recognize the laser parameter domain for Anderson localization. The exponential nature of the localization is proved, and we also identify the localization length. The tunneling of an Anderson-localized condensate with time is observed, and the revival phenomenon of Anderson localization is reported. Slowing down of Anderson localization is noticed for higher laser intensity. We also study the dynamical and structural stability of the condensate during Anderson localization, which suggests the preferred values of laser power and the time instance to encounter a minimal mean difference in the presence of noise.

We investigate the spectrum and structure of two heavy bosonic impurities immersed in a light boson system with noninteger dimensions $D$ by means of the Born-Oppenheimer approximation. The ratio between the energies of two consecutive many-body bound states, which follows an Efimov-type geometrical scaling law when the heavy-light pair has a resonant $s$-wave interaction, is found to be a function of the mass asymmetry, number of light bosons, and effective dimension $D$. Furthermore, the wave function is computed, and its behavior is explored for different system configurations. To exemplify our results, we consider mixtures of two heavy cesium atoms interacting with up to two lithium atoms, which are systems of current experimental interest.

By using a non-self-consistent many-body $T$-matrix theory, we calculate the finite-temperature Raman spectroscopy of a mobile impurity immersed in a Fermi bath in three dimensions. The dependencies of the Raman spectrum on the transferred momentum, temperature, and impurity-bath interaction are discussed in detail. We confirm that the peak in the Raman spectrum shows a weaker dependence on the impurity concentration than that in the radio-frequency spectroscopy due to the nonzero transferred momentum, as anticipated. We compare our theoretical prediction with the recent measurement by Gal Ness et al. [G. Ness, C. Shkedrov, Y. Florshaim, O. K. Diessel, J. von Milczewski, R. Schmidt, and Y. Sagi, Phys. Rev. X 10, 041019 (2020)] without any adjustable parameters. At weak coupling, we find a good quantitative agreement. However, close to the Feshbach resonance the agreement becomes worse. At strong coupling, we find that an unrealistic Fermi bath temperature might be needed to account for the experimental data.

Homodyne measurements are a widely used quantum measurement. Using a coherent state of large amplitude as the local oscillator, it can be shown that the quantum homodyne measurement limits to a field quadrature measurement. In this work, we give an example of a general idea: injecting nonclassical states as a local oscillator can lead to nonclassical measurements. Specifically, we consider injecting a superposition of coherent states, a Schrödinger cat state, as a local oscillator. We derive the Kraus operators and the positive operator-valued measure in this situation.

Genuine multipartite entanglement underlies correlation experiments corroborating quantum mechanics and it is an expedient empowering many quantum technologies. One of many counterintuitive facets of genuine multipartite entanglement is its ability to exhibit an emergent character. That is, one can infer its presence in some multipartite states merely from a set of its separable marginals. Here we show that the effect can also be found in the context of Gaussian states of bosonic systems. Specifically, we construct examples of multimode Gaussian states carrying genuine multipartite entanglement which can be verified solely from separable nearest-neighbor two-mode marginals. The key tool of our construction is an entanglement witness acting only on some two-mode reductions of the global covariance matrix, which we find by a numerical solution of a semidefinite program. We also propose an experimental scheme for preparation of the simplest three-mode state, which requires interference of three correlatively displaced squeezed beams on two beam splitters. Besides revealing the concept of emergent genuine multipartite entanglement in the Gaussian scenario and bringing it closer to experimentally testable form, our results pave the way to effective diagnostics methods of global properties of multipartite states without complete tomography.

The Rydberg formula along with the Ritz quantum defect ansatz has been a standard theoretical tool used in atomic physics since before the advent of quantum mechanics, yet this approach has remained limited by its nonrelativistic foundation. Here I present a long-distance relativistic effective theory describing hydrogenlike systems with arbitrary mass ratios, thereby extending the canonical Ritz-like approach. Fitting the relativistic theory to the hydrogen energy levels predicted by bound-state QED indicates that it is superior to the canonical, nonrelativistic approach. An analytic analysis reveals nonlinear consistency relations within the bound-state QED level predictions that relate higher-order corrections to those at lower order, providing guideposts for future perturbative calculations as well as insights into the asymptotic behavior of the Bethe logarithm. Applications of the approach include fitting to atomic spectroscopic data, allowing for the determination of the fine-structure constant from large spectral data sets and also to check for internal consistency of the data independently from bound-state QED.

We present a many-body theory for the interactions of two-dimensional exciton-polaritons beyond the Born approximation. Taking into account Gaussian quantum fluctuations via the Bogoliubov theory, we find that the exciton-exciton scattering is strongly renormalized by the light-matter coupling and acquires an inverse logarithmic dependence on the lower polariton energy. As a result, the polariton interaction strength may be enhanced at red photon-exciton detuning when the exciton-exciton scattering length is large. We also derive the exact Tan relations for exciton-polaritons, calculate Tan's contact coefficient and find an even more significant enhancement. Our predictions may provide a qualitatively correct guide for studies of exciton and polariton nonlinearities and suggest a route to achieving strongly nonlinear polariton gases.

The prospects of superradiant lasing on the 7.5-kHz-wide ${}^{1}S_0\text{−}{}^{3}P_1$ transition in ${}^{88}\mathrm{Sr}$ is explored by using numerical simulations of two systems based on realistic experimental numbers. One system uses the idea of demonstrating continuous superradiance in a simple, hot atom beam with high flux, and the other system is based on using ultracold atoms in a dipole guide. For the hot-beam system we consider a range of atom beam parameters as well as the impact of a scheme to discard fast atoms along the cavity axis. We find that the system achieves lasing above a flux of $2.5\times {10}^{12}$ atoms/s and that it is capable of outputting hundreds of nanowatts and suppressing cavity noise by a factor of 20–30. The relativistic transverse Doppler shifts cause a shift in the lasing frequency on the order of 500 Hz. For the cold-atom beam we account for decoherence and thermal effects when using a repumping scheme for atoms confined in a dipole guide. This is done by treating recoils and state-dependent forces acting on atoms in the dipole guide within the framework of the stochastic master equation. We find that the output power is on the order of hundreds of picowatts; however, transverse Doppler shifts can be neglected, and cavity noise can be suppressed on the order of a factor of 50–100. Additionally, we show that both systems exhibit local insensitivity to fluctuations in atomic flux.