We propose a potentially practical scheme to realize arbitrary quantum state transfer between two traveling atoms that go through a high-finesse cavity by using stimulated Raman adiabatic passage in an atom-cavity-laser system under a dissipative environment. By numerically simulating the dynamics of the system, we demonstrate quantitatively that the fidelities of the quantum state transferred between two atoms can be maximized by elaborately adjusting the peak amplitudes of the laser's Rabi frequency and the detuning of the Raman transition. Additionally, the noise effect from the atomic and cavity dissipation can reduce the fidelity. The experimental feasibility is justified using currently available technology.

Adiabatic evolution of light in parallel curved optical waveguide array is investigated theoretically. This problem is shown to bear a close connection with the process of coherent population transfer in a “bow-tie” model in quantum physics. Under certain conditions on the geometry of the waveguides and the optical properties of the system complete light transfer between the outer waveguides is achieved. Special attention is paid to the case of three waveguides, which is analyzed using the solutions of the well-known bow-tie model. The analytic solution is used to design recipes for creating arbitrary superpositions of light intensity between the waveguides, with possible applications in achromatic optical multiple-beam splitters. For more than three waveguides complete light transfer between the outer waveguides and beam splitting is demonstrated numerically.

Well-controlled nonlinear interactions between light-field pulses and single atoms could be used to implement optical quantum information technologies based on qubits encoded in superpositions of coherent states of light. Here, we investigate the transformation of a coherent light field input at a single atom sufficiently far from resonance to limit the decoherence effects associated with random excitations of the atom. The conditions for suppressing multiphoton scattering to implement arbitrarily large shifts of the coherent light amplitude without decoherence are studied. It is shown that quantum-controlled coherent shifts can be achieved by sufficiently long coherent pulses, indicating the possibility of generating superpositions of coherent states with large amplitude differences. The dominant multiphoton scattering effect associated with four-wave mixing is also identified, and the spectral and temporal characteristics of the entangled photon pairs generated by this process are discussed.

Cloning of arbitrary images from the spatial profile of a laser beam onto that of a second beam is theoretically investigated. The two fields couple to each other while propagating in an atomic $\Lambda$ medium displaying coherent population trapping in the case where probe and control fields have comparable strength. Our method is suitable to clone arbitrary images as demonstrated in numerical simulations where the three letters “CPT” are encoded in the control field profile. The cloned structures have features reduced in size by about a factor of 2, when compared to the initial control images, and are consistent with a recent related experiment.

When used to control the group velocity of light pulses, a microring resonator with loss often induces pulse splitting in addition to wearing down the pulse energy, whereas a gain microring resonator with identical dispersion can usually keep the pulse shape and make the pulse delay greater. Based on the symmetry between the transmission properties of microring resonators with gain and with loss and linear system theory, we illustrate the effects of gain and loss on pulse splitting and delay and reveal the mechanism by which gain improves the group-velocity control behaviors of the microring resonators.

We propose an entanglement criterion in terms of quantum Fisher information, which complements the criterion based on variance and local uncertainty relations [H. F. Hofmann and S. Takeuchi, Phys. Rev. A 68, 032103 (2003)]. We illustrate the significance of this criterion by showing that it can reveal entanglement undetectable by the variance method. The dual relation between the criterion based on quantum Fisher information and that based on variance are highlighted. The combination of these two criteria leads to a refined method for entanglement detection, which is stronger than when either one is used alone.

We examine a generalized Rabi model formed by two identical qubits interacting with a common oscillator mode. In the near-resonance configuration where the oscillator frequency is close to the transition frequency of the qubit, we determine the ground state of the model approximately by using a variational method and a transformation method. Both methods are shown to approximate the ground state accurately for a range of coupling strengths in the ultrastrong-coupling regime. In addition, the accuracy of the approximation can be further improved by using perturbation theory. We also characterize the ground-state entanglement between the two qubits by calculating the negativity.

The separability problem is formulated in terms of a characterization of a single entanglement witness. More specifically, we show that any (in general multipartite) state $\varrho$ is separable if and only if a specially constructed entanglement witness $W_{\varrho }$ is weakly optimal, i.e., its expectation value vanishes on at least one product vector. Interestingly, the witness can always be chosen to be decomposable. Our result changes the conceptual aspect of the separability problem and raises some questions about the properties of positive maps.

We have implemented a method based on the Feshbach formalism along with an explicitly correlated configuration interaction method to perform a systematic study on the behavior of resonance parameters (energies and lifetimes) of the autoionizing states of plasma-embedded He ${}^{1,3}{S}^e$, ${}^{1,3}{P}^o$, and ${}^{1,3}{D}^e$, as a function of the screening strength. In particular, we study the evolution of the lowest states in the series located below the He${}^{+}$($N=2$) ionization threshold in the unscreened case. At variance with one-electron atoms (where shape resonance widths vary monotonically with the screening strength) the evolution of the Auger width with respect to screening is found to be different for each series represented by ${(K,T)}^A$ pseudoquantum numbers until resonances merge into the upper electronic continuum, when crossing the He${}^{+}$(2$s$) threshold. We conclude from our ab initio calculations that, although resonances pertaining to the same ${(K,T)}^A$ series share a similar tendency in their widths against the screening strength, general propensity rules for the robustness of lifetimes, based on the isomorphic series in the ${(K,T)}^A$ classification, cannot be established in plasma-embedded helium.

Ionization mechanisms of C${}_{60}$ molecules irradiated by a short intense 800-nm laser pulse are studied. Angle-resolved photoelectron spectra show above-threshold ionization (ATI) patterns with a low peak contrast and a remarkably smooth angular distribution. The results are interpreted by combining two theoretical models. A time-dependent Schrödinger equation (TDSE) calculation based on the $B$-spline method that explicitly takes into account the molecular potential mimics the single-active-electron response while a statistical model accounts for the many-electron effects. We show that the latter are responsible for the loss of contrast in the ATI peaks. The smooth angular distribution arises in the TDSE calculation as a result of the high angular momentum of the C${}_{60}$ ground electronic state and therefore is a manifestation of the atomic behavior of the molecule.

We study the diffraction phase of different orders via the Dyson expansion series, for ultracold atomic gases scattered by a standing-wave pulse. As these diffraction phases are not observable in a single-pulse scattering process, a temporal Talbot-Lau interferometer consisting of two standing-wave pulses is demonstrated experimentally with a Bose-Einstein condensate to explore this physical effect. The role of the diffraction phases is clearly shown by the second standing-wave pulse in the relative population of different momentum states. Our experiments demonstrate obvious effects beyond the Raman-Nath method, while they agree well with our theory by including the diffraction phases. In particular, the observed asymmetry in the dependence of the relative population on the interval between two standing-wave pulses reflects the diffraction phase differences. The role of interatomic interaction in the Talbot-Lau interferometer is also discussed.

A multiwave atom interferometer using multiple Wannier-Stark states is experimentally realized in a vertical optical lattice. Atoms are coherently driven by stimulated Raman transitions into a superposition of several adjacent lattice sites, in which they evolve at multiples of Bloch frequency in the same internal state to form an interference pattern. We observe coherent evolution for more than 500 Bloch periods. The noise analysis shows that the phase resolution of this interferometer is detection noise limited. This multiwave interferometer could be a potential instrument for gravimetry and short-range forces measurement.

The collision of two clouds of Fermi gas at unitarity (UFG) has been recently observed to lead to shock waves whose regularization mechanism, dissipative or dispersive, is being debated. While classical, dissipative shocks, as in gas dynamics, develop a steep, localized shock front that translates at a well-defined speed, dispersively regularized shocks are distinguished by an expanding region of short wavelength oscillations with two speeds, those of the leading and trailing edges. For typical UFG experimental conditions, the theoretical oscillation length scale is smaller than the resolution of present imaging systems so it is unclear how to determine the shock type from its structure alone. Two experimental methods to determine the appropriate regularization mechanism are proposed: measurement of the shock speed and observation of a one-dimensional collision experiment with sufficiently tight radial confinement.

We study how macroscopic superpositions of coherent states produced by the nondissipative dynamics of binary mixtures of ultracold atoms are affected by atom losses. We identify different decoherence scenarios for symmetric or asymmetric loss rates and interaction energies in the two modes. In the symmetric case the quantum coherence in the superposition is lost after a single loss event. By tuning appropriately the energies we show that the superposition can be protected, leading to quantum correlations useful for atom interferometry even after many loss events.

We consider an effectively one-dimensional binary Bose-Einstein condensate (BEC) with nonlinear repulsive interactions and linear spin-orbit (SO) and Zeeman-splitting couplings. In the presence of the trapping harmonic-oscillator (HO) potential, we report the existence of even, odd, and asymmetric spatial modes. They feature alternating domains with opposite directions of the pseudospin, i.e., antiferromagnetic structures, which is explained by the interplay of the linear couplings, HO confinement, and repulsive self-interaction. The number of the domains is determined by the strength of the SO coupling. The modes are constructed analytically in the weakly nonlinear system. The dynamical stability of the modes is investigated by means of the Bogoliubov–de Gennes equations and direct simulations. A notable result is that the multi-domain-wall (DW) structures are stable, alternating between odd and even shapes, while the simplest single-DW structure is unstable. Thus, the system features a transition to the complex ground states under the action of the SO coupling. The addition of the Zeeman splitting transforms the odd modes into asymmetric ones via spontaneous symmetry breaking. The results suggest possibilities for switching the binary system between states with opposite (pseudo)magnetization by external fields, and realization of similar stable states and dynamical effects in solid-state and nonlinear-optical settings emulated by the SO-coupled BECs.

We study the spin dynamics of two magnetic chromium atoms trapped in a single site of a deep optical lattice in a resonant magnetic field. Dipole-dipole interactions couple spin degrees of freedom of two particles to their quantized orbital motion. A trap geometry combined with two-body contact $s$-wave interactions influence a spin dynamics through the energy spectrum of the two-atom system. Anharmonicity and anisotropy of the site results in a “fine” structure of two-body eigenenergies. The structure can be easily resolved by weak magnetic dipole-dipole interactions. As an example we examine the effect of anharmonicity and anisotropy of the binding potential on demagnetization processes. We show that weak dipolar interactions provide a perfect tool for precision spectroscopy of the energy spectrum of the interacting few particle system.

We experimentally and numerically show that single-wavelength emission can be stably observed for a fully chaotic microcavity laser with a stadium shape under continuous wave condition. The emission pattern is asymmetric with respect to the symmetry axes of the laser cavity, and it cannot be explained by a single cavity mode. On the basis of numerical analysis, we interpret such a lasing as the result of frequency-locking interaction among several low-loss cavity modes. Moreover, we experimentally investigate the optical spectral properties of the laser under pulsed-pumping condition, and discuss the pulse-width dependence on the number of lasing modes.

The semiclassical equations which describe lasing in nanowires are derived from first principles. Both the lasing threshold condition and the steady-state regime of operation are discussed. It is shown that the lasing is governed by the Fourier coefficients of the field susceptibility averaged over the nanowire cross section. The general theory is illustrated by the case where a nanowire supports a single Fabry-Pérot mode originated from a transverse magnetic waveguide mode. Basing on the developed theory, the possibility of lasing without inversion is predicted and the corresponding nanolaser cavity is designed.