We report a measurement of the dimensionless enhancement factor ${\kappa }_0$ for the Rb-${}^{129}\mathrm{Xe}$ pair commonly used in spin exchange optical pumping (SEOP) to produce hyperpolarized ${}^{129}\mathrm{Xe}$. ${\kappa }_0$ characterizes the amplification of the ${}^{129}\mathrm{Xe}$ magnetization contribution to the Rb electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement is carried out in Rb vapor cells containing both ${}^3\mathrm{He}$ and ${}^{129}\mathrm{Xe}$ and relies on the previously measured value of ${\kappa }_0$ for the Rb-${}^3\mathrm{He}$ pair. The measurement is based on (1) the optically detected (Faraday rotation) frequency shift of the ${}^{87}\mathrm{Rb}$ electron paramagnetic resonance (EPR) hyperfine spectrum caused by the SEOP nuclear polarization and subsequent sudden destruction of nuclear polarization of both species and (2) a comparison of nuclear magnetic resonance signals for the two species acquired just prior to the EPR frequency shift measurements. We find ${\left({\kappa }_0\right)}_{\mathrm{RbXe}}=518\pm 8$, in good agreement with previous measurements and theoretical estimates but with improved precision.

We study the hyperfine spectrum of atoms of ${}^{87}\mathrm{Rb}$ dressed by a radio-frequency field and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap, and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant sidebands spaced (in frequency) at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing field. We theoretically explain the main features of the microwave spectrum using a semiclassical model in the low-field limit and the rotating-wave approximation for alkali-metal-like species, in general, and ${}^{87}\mathrm{Rb}$ atoms, in particular. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing configuration and the probing microwave field.

In the present work, we demonstrate that structured light beams are constituted by two traveling waves which transverse components are in opposite directions, that is, incoming and outgoing from the axis of propagation. These waves result from the complex sum of the two fundamental solutions of the transverse component of the spatial wave equation. After a partial obstruction of the beam, the incoming and outgoing waves can be easily observed during the self-healing process, providing a simple explanation of the phenomenon. Incoming and outgoing waves in Laguerre-Gauss beams are investigated analytically, numerically, and experimentally. The proposed way to describe light beams might offer new insights into the phenomenon of diffraction.

We theoretically investigate the conditions for the emergence of lateral (recoil) optical forces on generic dipole-type emitters positioned nearby a reciprocal translation-invariant substrate. Surprisingly, we find that for linearly polarized electric dipoles and for a gradientless excitation the lateral force invariably vanishes, independent of the anisotropy (e.g., tilted optical axes) or chirality of the substrate. We identify an opportunity to have a recoil force relying on a superposition of two linearly polarized and collinear electric and magnetic dipoles. Counterintuitively, it is shown that when such an emitter stands above a uniaxial dielectric half-space with tilted optical axes it may experience a recoil force oriented along the direction perpendicular to the plane defined by the interface normal and the substrate optical axis.

We systematically investigate the optical analogs of quantum relativistic Jackiw-Rebbi states in binary waveguide arrays in the presence of the Kerr nonlinearity with both self-focusing and self-defocusing cases. The localized profiles of these nonlinear Jackiw-Rebbi states can be calculated exactly by using the shooting method. We show that these nonlinear Jackiw-Rebbi states have a very interesting feature which is totally different from all other well-known nonlinear localized structures, including optical solitons. Namely, the profiles of nonlinear Jackiw-Rebbi states with higher peak amplitudes can totally envelope those with lower peak amplitudes. We demonstrate that media with the positive nonlinear coefficient can support stable Jackiw-Rebbi states for a wide range of peak amplitudes, whereas media with the negative nonlinear coefficient are only able to support Jackiw-Rebbi states with low peak amplitudes. A general rule for the detuning of nonlinear Jackiw-Rebbi states in binary waveguide arrays is found.

Atomic-ensemble spin waves carrying single-photon Fock states exhibit nonclassical many-body correlations in between atoms. The same correlations are inherently associated with single-photon superradiance, forming the basis of a plethora of quantum light-matter interfaces. We devise a scheme allowing the preparation of spatially structured superradiant states in the atomic two-photon cascade using spin-wave light storage. We thus show that long-lived atomic ground-state spin waves can be converted to photon pairs, opening the way towards nonlinear optics of spin waves via multi-wave-mixing processes.

We propose a realization of the quantum switch for coherent light fields for the fiber-coupled microdisk cavities. We demonstrate by combining numerical and analytical methods that both in strong coupling and bad cavity limits it is possible to change a system's behavior from being fully transparent to being fully reflective by varying the amplitude of the external control field. We remark that tuning the amplitude of the control field instead of cavity-atom coupling strength, which was suggested by S. Parkins et al., [Phys. Rev. A 90, 053822 (2014)] for two-level atoms and works only in the strong coupling limit, brings more control and tunability over the transmitted and reflected intensities. We also demonstrate the possibility of controlling the statistics of the input coherent field with the control field which opens the venue for obtaining quantum states of light.

The elastic scattering properties of three bosons at low energy enter the many-body description of ultracold Bose gases via the three-body scattering hypervolume $D$. We study this quantity for identical bosons that interact via a pairwise finite-range potential. Our calculations cover the regime from strongly repulsive potentials towards attractive potentials supporting multiple two-body bound states and are consistent with the few existing predictions for $D$. We present a numerical confirmation of the universal predictions for $D$ in the strongly interacting regime, where Efimov physics dominates, for a local nonzero-range potential. Our findings highlight how $D$ is influenced by three-body quasibound states with strong $d$-wave or $g$-wave characteristics in the weakly interacting regime.

Here, we explore the prospects of carrying out the single qubit spectroscopy of environmental noise when the resolution of the frequency filters produced by the dynamical decoupling pulse sequences can be set high enough to reveal the discrete structure of the noise spectral density. The standard form of spectroscopy is applicable when the filter is unable to resolve the discrete spectral lines and only coarse-grained approximation of the spectrum is recorded in the qubit's decoherence rate. When the discrete structure becomes accessible, the qubit probe evolves in a qualitatively different manner, and the procedure for recovering spectral density has to be redesigned.

We investigate the feasibility of quantum seals. A quantum seal is a state provided by Alice to Bob along with information that Bob can use to make a measurement, “break the seal,” and read the classical message stored inside. There are two success criteria for a seal: the probability Bob can successfully read the message without any further information from Alice must be high, and if Alice asks for the state back from Bob, the probability Alice can tell if Bob broke the seal without permission must be high. We build on the work of Chau [Phys. Rev. A 75, 012327 (2007)], which gave optimal bounds on these criteria, showing that they are mutually exclusive for high probability. We weaken the assumptions of this previous work by providing Bob with only a classical description of a prescribed measurement, rather than classical descriptions of the possible seal states. We show that this weakening does not affect the bounds but does simplify the analysis. We also prove upper and lower bounds on an alternative operational metric for measuring the success criteria.

We introduce a hybrid quantum-classical adversarial machine learning architecture called a quantum-classical associative adversarial network (QAAN). This architecture consists of a classical generative adversarial network with a small auxiliary quantum Boltzmann machine that is simultaneously trained on an intermediate layer of the discriminator of the generative network. We numerically study the performance of QAANs compared to their classical counterparts on the MNIST and CIFAR-10 data sets, and show that QAANs attain a higher quality of learning when evaluated using the Inception score and the Fréchet Inception distance. As the QAAN architecture only relies on sampling simple local observables of a small quantum Boltzmann machine, this model is particularly amenable for implementation on the current and next generations of quantum devices.

We present an experimental observation of the visible magnetic dipole transition between the fine structure levels in the ground term of ${\mathrm{Ba}}^{6+}$ ($5s{}^{2}5p^2$: ${}^{3}P_0-{}^{3}P_1$) with a compact electron beam ion trap. The wave number in vacuum of the transition is determined to be 15505.506(37) ${\mathrm{cm}}^{-1}$ by simultaneously observing the reference lines of neutral Ne. The present measurement reduces the uncertainty in the previously reported value obtained from observation of the electric dipole transitions to the ground terms in the extreme ultraviolet range [Phys. Scr. 46, 403 (1992)].

An extremely active research topic of modern optics is studying how light can be engineered to possess forms of structure such as a twisting or a helical phase and the ensuing optical orbital angular momentum (OAM) and its interactions with matter. In such circumstances, the plane-wave description no longer suffices and both paraxial and nonparaxial solutions to the wave equation are desired. Within the framework of molecular QED theory, a general formulation is developed for the scattering of twisted light beams by molecular systems through the Kramers-Heisenberg dispersion formula and ensuing scattering cross section, which takes account of the effects of the phase and intensity structure of twisted light, revealing scattering effects not exhibited by unstructured, plane-wave light. The theory is applicable to linear scattering as well as to nonlinear optical effects for both chiral and nonchiral species, and explicit results are derived for Rayleigh and Raman scattering (including second-order contributions), Rayleigh and Raman optical activity, and their circular-vortex differential scattering analogs. These processes necessitate the inclusion of magnetic-dipole and electric-quadrupole coupling terms, as well as the usual leading electric-dipole interaction term. It is seen that the coupling of electric quadrupole moments to structured light affords a unique sensitivity to the phase properties of the beam, most importantly, its optical OAM, and its inclusion permits the contribution to the scattering cross section proportional to the square of the mixed electric dipole-quadrupole polarizability to be evaluated for which interesting features result. These include its discriminatory behavior arising from circularly polarized input radiation and its dependence on the topological charge, which can also serve to enhance scattering. Also presented are results for a contribution of identical order proportional to the pure electric-dipole and quadrupole polarizabilities.

We investigate the ionization dynamics of one-electron model diatomic molecules with different orbital symmetries ($1{\sigma }_g$ and $1{\sigma }_u$) in a strong laser field via the full three-dimensional time-dependent Schrödinger equation. It is shown that the ionization probabilities of the molecules with different initial states ($1{\sigma }_g$ and $1{\sigma }_u$) oscillate out of phase vs internuclear distance, and the photoelectron spectra of the aforementioned two molecules also show out-of-phase oscillation structures. The above intriguing features are well reproduced by the simulations of the length-gauge strong-field approximation, which can be ascribed to the distinct interferences of electronic wave packets released from different atomic centers.

Atom interferometry using stimulated Raman transitions in a retroreflected configuration is the first choice in high-precision measurements because it provides low phase noise, a high-quality Raman wave front, and a simple experimental setup. However, it cannot be used for atoms at zero velocity because two pairs of Raman lasers are simultaneously resonant. Here we report a method which allows this degeneracy to be lifted by using a frequency chirp on the Raman lasers. Using this technique, we realize a Mach-Zehnder atom interferometer hybridized with a force balanced accelerometer which provides horizontal acceleration measurements with a short-term sensitivity of $3.2\times {10}^{-5}{\mathrm{m}\mathrm{s}}^{-2}/\sqrt{\text{Hz}}$. This technique could be used for multiaxis inertial sensors, tiltmeters, or atom interferometry in a microgravity environment.

We numerically study the Anderson localization in an oscillating one-dimensional Rydberg-dressed Bose-Einstein condensate with weak random disorder in which the range of the interaction, the blockade radius $R_{\mathrm{c}}$, is variable. Without disorder, the uniform system can undergo a superfluid-supersolid transition at $R_{\text{c}}=l_{\mathrm{c}}\simeq 1.7{\xi }_0$ with ${\xi }_{\text{0}}$ the zero-range healing length. When ${\xi }_0$ exceeds the disorder correlation length ${\sigma }_{\mathrm{D}}$, we show that exponential localization occurs in the equilibrium condensate when $R_{\mathrm{c}}\le l_{\mathrm{c}}$, while Gaussian localization occurs when $R_{\mathrm{c}}>l_{\mathrm{c}}$. The latter suggests that the $k$ wave for a long-ranged interacting system could decay Gaussianly with weak random disorder.

We study the quantum fluctuations in the condensates of a mixture of bosonic atoms and molecules with interspecies $p$-wave interaction. Our analysis shows that the quantum phase of coexisting atomic and molecular condensates is unstable at the mean-field level. Unlike the mixture of $s$-wave interaction, the Lee-Huang-Yang correction of $p$-wave interaction is unexpectedly found here to exhibit an opposite sign with respect to its mean-field term above a critical particle density. This quantum correction to the mean-field energy provides a remarkable mechanism to self-stabilize the phase. The order parameter of this superfluid phase carries opposite finite momenta for the two atomic species while the molecular component is a polar condensate. Such a correlated order spontaneously breaks a rich set of global U(1) gauge, atomic spin, spatial rotation and translation, and time-reversal symmetries. For potential experimental observation, the phenomenon of anisotropic polar superfluid droplets is predicted to occur when the particle number is kept finite.

Achieving exact unidirectional invisibility in a finite frequency band has been an outstanding problem for many years. We offer a simple solution to this problem in two dimensions that is based on our solution to another more basic open problem of scattering theory, namely, finding potentials $v(x,y)$ whose scattering problem is exactly solvable via the first Born approximation. Specifically, we find a simple condition under which the first Born approximation gives the exact expression for the scattering amplitude whenever the wave number for the incident wave is not greater than a given critical value $\alpha$. Because this condition only restricts the $y$ dependence of $v(x,y)$, we can use it to determine classes of such potentials that have certain desirable scattering features. This leads to a partial inverse scattering scheme that we employ to achieve perfect (nonapproximate) broadband unidirectional invisibility in two dimensions. We discuss an optical realization of the latter by identifying a class of two-dimensional isotropic active media that do not scatter incident transverse waves with wave numbers in the range $(\alpha /\sqrt{2},\alpha ]$ and source located at $x=\infty$ while scattering the same waves if their source is relocated to $x=-\infty$.

In this article, we reconstruct the Frauchiger and Renner argument, taking into account that the assertions of the argument are made at different times. To do this, we use a formalism of quantum histories, namely the Theory of Consistent Histories. We show that the supposedly contradictory conclusion of the argument requires computing probabilities in a family of histories that does not satisfy the consistency condition, i.e., an invalid family of histories for the theory.

We calculated the nonlinear screening and the electronic stopping of energetic helium ions in a III-V compound semiconductor at low speeds below stopping maximum under channeling conditions. For the range of velocity considered, it is found the energy loss of the intruding ions show pronounced dependence on the electronic screening from the induced charge. Different with the prevalent scenario described by free-electron gas model that the induced charge distribution lags behind the projectile forming the so-called wake potential. We found through real-time time-dependent density functional theory that the induced charge by the channeling ion keeps oscillating back and front when channeling through the zinc-blende crystalline GaN, which is interpreted as a consequence of temporally oscillating Coulomb field arising from the periodical atomic arrangement along ion trajectory. When one of the frequencies coincides with the transition energy of the ionic charge, it would be resonantly excited by the oscillating field, which further gives rise to a depletion in electronic screening by bound electrons to the ion, resulting in odd enhanced stopping trend at narrow velocity windows.