We theoretically demonstrate intermittent chaos induced by radiation-pressure nonlinearity in a general optomechanical system. In contrast to the periodic and chaotic dynamics, this optomechanical intermittent chaos is characterized by a nearly periodic motion interrupted irregularly by the chaotic motion, and exists in a transitional parameter regime between the normal chaos and periodic windows. The route to intermittent chaos is identified by bifurcation diagrams, and the optimal parameter regime for achieving this intermittent chaos is presented by a phase diagram. This work broadens the realm of optomechanical nonlinear dynamics, and is feasible with currently available optomechanical technology.

Spontaneous decay of an excited atom in a waveguide is essentially modified by the spatial structure of a vacuum reservoir. This is particularly exciting in view of a range of applications for quantum information science. We found out that spontaneous decay can be incomplete, so the time dependence of the excited state population asymptotically approaches to a nonzero value, under the conditions when the atomic transition frequency is larger than the cutoff frequency of a waveguide and far from the vicinities of the cutoffs. The discovered effect is explained by the emergence of the dark state, which is nondecaying due to polarization selection rules. It was revealed for a single-mode waveguide with rectangular cross section both in a single-atom case and a diatomic case when the long-range dipole-dipole interaction plays a significant role.

We study the distinguishability of photons in multiphoton interference on a multiport when fast detectors, capable of precise time resolution, are employed. Such a setup was previously suggested for experimental realization of boson sampling with single photons. We investigate if fast photodetection allows us to circumvent distinguishability of realistic single photons in mixed states. To this goal, we compare distinguishability of photons in two setups: (a) with photons in the same average (temporal) profile on a spatial interferometer and photodetection incapable of (or with strongly imprecise) time resolution and (b) with photons in generally different average temporal profiles on the same spatial interferometer and photodetection with precise time resolution. Exact analytical results are obtained for Gaussian-shaped single photons with Gaussian distribution of photon arrival time. Distinguishability of photons in the two setups is found to be strikingly similar. For the same purity of photon states, only the same quality experimental boson sampling can be achieved using either of the two setups. The upshot of our results is that distinguishability due to mixed states is an intrinsic property of photons, whatever the photodetection scheme.

We derive upper and lower bounds on the Casimir-Polder force between an anisotropic dipolar body and a macroscopic body, separated by vacuum, via algebraic properties of Maxwell's equations. These bounds require only a coarse characterization of the system—the material composition of the macroscopic object, the polarizability of the dipole, and any convenient partition between the two objects—to encompass all structuring possibilities. We find that the attractive Casimir-Polder force between a polarizable dipole and a uniform planar semi-infinite bulk medium always comes within 10% of the lower bound, implying that nanostructuring is of limited use for increasing attraction. In contrast, the possibility of repulsion is observed even for isotropic dipoles, and is routinely found to be several orders of magnitude larger than any known design, including recently predicted geometries involving conductors with sharp edges. These results may have ramifications for the design of surfaces to trap, suspend, or adsorb ultracold gases.

The electron affinity of thallium has been precisely measured using laser photodetachment threshold spectroscopy. The relative photodetachment cross section from the negative ion ${}^{205}\mathrm{Tl}^{-}$ was measured using a tunable infrared laser over the photon energy range 300–900 meV (4130–1380 nm). A pair of closely spaced $s$-wave thresholds were observed due to transitions from the negative ion ground state $\mathrm{T}{\mathrm{l}}^{-}$ $\left(6p^2{}^{3}P_0\right)$ to the two hyperfine levels of the neutral atom ground state Tl $(6p{}^{2}P_{1/2},$ $F=0,1)$, which determines the electron affinity of ${}^{205}\mathrm{Tl}$ to be 320.053(19) meV. These results substantially improve the precision of the Tl electron affinity and resolve long-standing discrepancies in the literature between previous experimental and theoretical values.

Generation of propagating electron vortex states in ionization of ${\mathrm{H}}^{-}$ by short, circularly polarized laser pulses is studied within the strong-field approximation. The latter, being particularly suitable for treating negative ions, is shown to be gauge independent for an $s$-electron system like ${\mathrm{H}}^{-}$. Most importantly, it is demonstrated that the orbital angular momentum from the laser field can be efficiently transferred to photoelectrons, thus resulting in high orbital angular momenta electron vortex states. The conditions for this to happen are formulated and visualized with the help of coarse-grained probability distributions of photoelectrons, which are calculated by Monte Carlo method.

Exploiting the multiple long pulse capability and suite of x-ray diagnostics of the Orion laser, we have set out to explore line coincidence photopuming—the enhancement in population of an atomic level brought on by resonant absorption of x rays from a different emitting ion. Unlike previous work, the two ions are in the same plasma and so the experiment is an x-ray analog of the well-known Bowen resonance fluorescence mechanism that operates in astrophysical situations in the optical region. Our measurements have shown enhanced fluorescence in a chlorine plasma, attributable to line coincident photopumping from co-mixed potassium ions. To detect this relatively low signal-to-noise phenomenon, the data from multiple shots are combined, and the statistical method of bootstrapping is used to assign a confidence value to the measured enhancement, resulting in an estimate of the enhancement of $39{\pm }_{18}^{16}\%$ compared to the null case, where no pumping occurs. The experimental results have been compared to coupled radiation-transport and radiation hydrodynamics simulations using the cretin code together with the nym radiation hydrodynamics model and agreement has been found, with the simulations also predicting modest enhancement.

The atom-based traceable standard for microwave electrometry shows promising advantages by enabling stable and uniform measurement. Here we theoretically propose and then experimentally realize an alternative direct International System of Units (SI)–traceable and self-calibrated method for measuring a microwave-electric-field strength based on electromagnetically induced absorption (EIA) in cold Rydberg atoms. Comparing with the method of electromagnetically induced transparency, we show that the equivalence relation between the microwave Rabi frequency and Autler-Townes splitting is more valid and is even more robust against the experimental parameters in the EIA's linear region. Furthermore, a narrower linewidth of cold Rydberg EIA enables us to realize a direct SI-traceable microwave-electric-field measurement as small as $\sim 100\mu \mathrm{V}{\mathrm{cm}}^{-1}$.

We address the consequences of back action in the unidirectional coupling of two cascaded open quantum subsystems connected to the same reservoir at different spatial locations. In the spirit of H. J. Carmichael [Phys. Rev. Lett. 70, 2273 (1993)], the second subsystem is a two-level atom, while the first transforms from a driven empty cavity to a perturbative QED configuration and ultimately to a driven Jaynes-Cummings (JC) oscillator through a varying light-matter coupling strength. For our purpose, we appeal at first to the properties of resonance fluorescence in the statistical description of radiation emitted along two channels—those of forward and sideways scattering—comprising the monitored output. In the simplest case of an empty cavity coupled to an external atom, we derive analytical results for the nonclassical fluctuations in the fields occupying the two channels, pursuing a mapping to the bad-cavity limit of the JC model to serve as a guide for the description of the more involved dynamics. Finally, we exemplify a conditional evolution for the composite system of a critical JC oscillator on resonance coupled to an external monitored two-level target, showing that coherent atomic oscillations of the target probe the onset of a second-order dissipative quantum phase transition in the source.

Optical modes possessing orbital angular momentum constitute a very useful platform for experimental studies on the quantum limits of thermodynamics. Here, we present experimental results for entangled photon pairs subjected to thin turbulence simulated with spatial light modulators and interpret them in the context of the generalized Jarzynski's fluctuation relation. By holographic measurement of the orbital angular momentum, we obtain the work distribution produced by the turbulence for single- and double-sided turbulence channels. The use of Klyshko's advanced-wave picture allows us to interpret the experimental scheme as a two-way process in a fully quantum picture.

Landauer's principle provides a perspective on the physical meaning of information as well as on the minimum working cost of information processing. Whereas most studies have related the decrease in entropy during a computationally irreversible process to a lower bound of dissipated heat, recent efforts have also provided another lower bound associated with the thermodynamic fluctuation of heat. The coexistence of the two conceptually independent bounds has stimulated comparative studies of their close relationship or tightness; however, these studies were concerned with finite quantum systems that allowed the revival of erased information because of a finite recurrence time. We broaden these comparative studies further to open quantum systems with infinite recurrence times. By examining their dependence on the initial state, we find the independence of the thermodynamic bound from the initial coherence, whereas the entropic bound depends on both the initial coherence and the population. A crucial role is indicated by the purity of the initial state: The entropic bound is tighter when the initial condition is sufficiently mixed, whereas the thermodynamic bound is tighter when the initial state is close to a pure state. These trends are consistent with previous results obtained for finite systems.

The electron-impact double ionization (DI) and triple ionization (TI) for O ii-iv ions are investigated using multistep approaches within the framework of many-body perturbation theory. The indirect DI and TI are treated as the single ionization of an inner-shell $1s$ electron followed by the single and double Auger decays, respectively. The knockout mechanism is employed to deal with the direct ionization process. The present approaches reproduce the available experimental cross sections for the DI of O ii-iv ions with much better accuracy compared to previous calculations. The TI cross sections of the O ii ion are calculated, which are in good agreement with the recent experimental data [Lecointre et al., J. Phys. B 46, 205201 (2013)]. It is found that the electron correlation effect and the energy distribution of the intermediate electron, which is taken as the incident electron of the subsequent knockout process, play an important role in the multistep treatment of the multiple ionization process.

We study light scattering by systems combining randomly rough surface and volume dielectric fluctuations. We introduce a general model including correlations between surface and volume disorders, and we study the scattering properties within a single-scattering approach. We identify different regimes of surface and volume dominated scattering depending on length scales characterizing the surface and volume disorders. For uncorrelated disorders, we discuss the polarization response of each source of disorder, and show how polarimetric measurements can be used to separate the surface and volume contributions in the total measured diffusely scattered intensity. For correlated systems, we identify two configurations of volume disorder which, respectively, couple weakly or strongly to surface scattering via surface-volume cross correlations. We illustrate these effects on different configurations exhibiting interference patterns in the diffusely scattered intensity, which may be of interest for the characterization of complex systems or for the design of optical components by engineering the degree of surface-volume correlations.

When a gas of ultracold atoms is suddenly illuminated by light that is nearly resonant with an atomic transition, the atoms cannot respond instantaneously. This noninstantaneous response means the gas is initially more transparent to the applied light than in steady state. The timescale associated with the development of light absorption is set by the atomic excited-state lifetime. Similarly, the index of refraction in the gas also requires time to reach a steady-state value, but the development of the associated phase response is expected to be slower than absorption effects. Faraday rotation is one manifestation of differing indices of refraction for orthogonal circular light polarization components. We have performed experiments measuring the time-dependent development of polarization rotation in an ultracold gas subjected to a magnetic field. Our measurements match theoretical predictions based on solving optical Bloch equations. We are able to identify how parameters such as steady-state optical thickness and applied magnetic field strength influence the development of Faraday rotation.

This paper investigates the performance optimization of optically pumped magnetometers under zero-field parametric modulation. Based on the analytical solutions of the Bloch equation, both longitudinal and transverse modulations are studied experimentally. To estimate the nonuniform polarization distribution of alkali-metal atoms in the vapor cell, an average pumping rate model is proposed. Furthermore, the accuracy of this model and the measurement of the transverse relaxation rate are verified via the agreement between experimental and theoretical values. The results indicate that optimal performance can be achieved by employing a suitable modulation field, the selection of which is related to the modulation index $u$ in the Bessel series and the pump-light intensity. Although both operating modes show similar responses to weak magnetic fields, their effects on pump-light intensity are different due to the means of detecting atomic polarization. An optimal value of the pump-light intensity on the response strength exists in longitudinal modulation. However, with regard to transverse modulation, the sensitivity under weak pump-light intensity is better. This research has far-reaching significance for cases when the parametric modulation is manipulated.

We show that the stray field generated by isolated magnetic skyrmions can be used to trap ultracold atoms. Especially, ring-shaped and double-well trapping potentials for ultracold atoms can be created by combining the field from two isolated skyrmions. The geometry size, potential barrier, trapping frequency, and Majorana loss rate of these magnetic traps can be tuned by an external magnetic field or device configuration. The results here could be useful to develop atomtronics devices by manipulating magnetic skyrmions with modern spintronics techniques.

We investigate the low-temperature properties of an ultracold gas made of bosonic alkali-metal atoms with finite-range interaction under the effect of a disordered environment. The statistical characterization of the disorder is investigated within an effective-field-theory formalism for a generic spatial dimension $d$. Moving to $d=3$, where all the arising divergences are properly regularized, we focus on the depletion of both the condensate and superfluid densities. At zero temperature we obtain meaningful analytical formulas for the condensate fraction and the superfluid fraction which take into account the interplay among scattering length, effective range, and disorder strength.