In a microcavity laser, it is known that the quality factor obtained experimentally is much less than the one obtained numerically. This quality factor degradation in experiment is caused by various effects, such as absorption, surface roughness, flatness of the ridge boundary, and curvature. To understand the quality-factor degradation we obtain the gain and the internal loss coefficient in an elliptic microcavity laser. In the experiment, we take a triangular orbit. To confirm the triangular orbit, we measure the mode spacing and estimate the emission direction by including the Fresnel filtering. By using the Fourier transform analysis, we obtain the loss and gain coefficients because the triangular orbit can be regarded as a Fabry-Perot resonator due to the incidence angle. The obtained loss for our microcavity laser is larger than the one caused by material absorption, which is due to environmental losses, such as surface roughness and flatness of the ridge boundary.

Metamaterials featuring negative real parts of constitutive parameters have brought out a new kind of waveguide mode called a surface mode by forming interfaces with conventional dielectrics. These modes have a very interesting feature: the optical power guided through them can flow backward in metamaterial layers although the overall power moves forward. In this paper, we investigate the source of this backward power flow and show that, although the surface mode does not have any transverse wave vector, there always exists instantaneous power flow along the transverse direction, from metamaterial to dielectric layers and vice versa. The power transported in this way becomes the very source of the backward power flow. Using this power transport viewpoint, we reveal the differences among the surface modes guided through various kinds of interfaces.

We have theoretically characterized a negative-index metamaterial (NIM) slab with the aid of an entangled photon pair using a modified Hong-Ou-Mandel interferometer. The results we obtained show that the absorption and dispersion properties of the NIM slab can be distinguished in the profile of the fourth-order interference; thus, we can retrieve such parameters easily. A comparison with a coherent light shows the advantages with a quantum field.

Cooling mechanical resonators to a quantum regime at high temperatures is important in terms of exploring and applying their quantum effects unrestricted by low environmental temperatures. It has been suggested by M. Bhattacharya et al. [Phys. Rev. A 77, 033819 (2008)] that quadratic coupling could be used to help cool a membrane in membrane-in-the-middle optomechanical systems (MMOSs) at room temperature to a state with a mean phonon number smaller than 1. Its cooling effect is actually overestimated because of the unconsidered factor that it is limited by the small frequency difference between the quadratically coupled cavity mode and its neighboring mode, which imposes an upper bound on the input trapping laser power and therefore restricts its cooling effect. Based on the MMOS and by taking the above factors into consideration, we have concretely investigated the performance of this cooling method by a more rigorous calculation. Our calculation shows that the cooling effect is indeed ultimately limited by the input trapping laser power, but one can still cool a membrane close to a quantum regime at 77 K with parameters approaching experimental values.

We report experimental evidence of bistable phase locking in nonlinear optics, in particular, in a photorefractive oscillator emitting in few transverse modes. Bistable phase locking is a recently proposed method for converting a laserlike system, which is phase invariant, into a phase-bistable one by injecting a suitable spatially modulated monochromatic beam, resonant with the laser emission, into the optical cavity. We experimentally demonstrate that the emission on the fundamental TEM${}_{00}$ mode becomes phase bistable by injection of a beam with the shape of the TEM${}_{10}$ mode with appropriate frequency, in accordance with recent theoretical predictions [K. Staliunas et al., Phys. Rev. A 80, 025801 (2009)]. The experimental observations are supported by an analytical study of a few-transverse-mode photorefractive oscillator model.

We report a distinguished mechanism of using two interaction-free (uncoupled) cavities to realize an all-optical silicon diode with an extremely high contrast ratio. In contrast to existing examples of all-optical diodes, our unidirectional transmission results from mimicking Fano resonance in a compact and finite silicon waveguide. A Fano spectrum with an arbitrary asymmetric factor, resonant center, and linewidth is explicitly designed with two symmetric resonances, which can be separately realized and tuned in an insightful manner by two cascaded uncoupled cavities. The field localizations are inherently asymmetric. We show that if these double asymmetries (Fano spectrum and field localization) are integrated and controlled, an ultrahigh-contrast-ratio silicon Fano diode is accomplished. This finding provides a promising avenue for achieving an extremely compact optical switch and incorporating Fano resonance in silicon photonics.

We consider weak measurements (WMs) of a spin observable in quantum mechanics beyond the usual asymptotic regime. This is done by obtaining the exact time-dependent wave functions of the measuring apparatus for general nonideal measurements. Ideal strong measurements and the usual WM regime are obtained as the two extreme limiting cases of our exact treatment. We show that in the intermediate regime nonideal measurements lead to “semiweak” eccentric values that differ from the usual weak values. We further show that even in the WM regime the exact treatment leads to a meter behavior that can be markedly distinct from the one predicted by the usual WM formalism. We give several illustrations and discuss an application to the distinction of different realizations of the same density matrix.

We report an ab initio calculation of the shielding of the nuclear magnetic moment by the bound electron in hydrogenlike ions. This investigation takes into account several effects that have not been calculated before to our knowledge (electron self-energy, vacuum polarization, nuclear-magnetization distribution), thus bringing the theory to the point where further progress is impeded by the uncertainty due to nuclear-structure effects. The QED corrections are calculated to all orders in the nuclear binding strength parameter and, independently, to the leading order in the expansion in this parameter. The results obtained lay the groundwork for the high-precision determination of nuclear magnetic dipole moments from measurements of the $g$ factor of hydrogenlike ions.

We report the perpendicular plane ionization results of ($e$, 2$e$) triple-differential cross sections for the Ne(2$p$) and Ar(3$p$) atoms at the incident electron energies ranging from 5 to 50 eV above ionization potential for neon atoms and from 2 to 50 eV above ionization potential for the argon atoms. The present investigation has been done in the modified distorted wave Born approximation and it has been observed that postcollision interaction and polarization of target are important in the perpendicular plane ionization of atoms. We also present the results of triple-differential cross section for the doubly symmetric coplanar ionization of Na(3$s$) atoms at the incident electron energy ranging from 6 to 60 eV above ionization potential. Thus we are able to see the effects of target polarization and postcollision interaction in coplanar as well as the perpendicular plane geometrical conditions. The results of our calculations for the Ne(2$p$) and Ar(3$p$) have been compared with the very recent measurements of Nixon et al. [K. L. Nixon, A. J. Murray, and C. Kaiser, J. Phys. B 43, 085202 (2010)] and the results of coplanar ionization of Na(3$s$) have been compared with the experimental data of Murray [A. J. Murray, Phys. Rev. A 72, 062711 (2005)]. It is observed that there are certain discrepancies between theoretical and experimental results which indicate that further theoretical efforts are required to understand the cross section trends of neon, argon, and sodium atoms. The cross section in the perpendicular plane ionization exhibits complex variations as a function of incident energy and target.

The electron-capture processes in collisions of B${}^{2+}$ ions with neon and argon targets have been studied theoretically using ab initio multireference configuration interaction potential-energy curves and nonadiabatic couplings. The cross sections for the simple capture process have been calculated using the semiclassical collision methods in the 10${}^{-2}$–2-a.u. velocity range ($E_{\mathrm{lab}}$ ≈ [0.02–1080 keV]) and have been compared with the available experimental data. The charge-transfer mechanism is analyzed with regard to the radial and rotational interactions and appears to be quite different for both systems. Good agreement is found with the measured cross sections.

We present a theoretical treatment for the ejection of a secondary electron from a clean metallic surface induced by the impact of a fast primary electron. Assuming a direct scattering between the incident, primary electron and the electron in a metal, we calculate the electron-pair energy distributions at the surfaces of Al and Be. Different models for the screening of the electron-electron interaction are examined, and the footprints of the surface- and the bulk-plasmon modes are determined and analyzed. The formulated theoretical approach is compared with the available experimental data on the electron-pair emission from Al.

We propose a realistic experimental setup for creating quasi-two-dimensional (2D) bright solitons in dipolar Bose-Einstein condensates (BECs), the existence of which was proposed by Tikhonenkov et al. [Phys. Rev. Lett. 100, 090406 (2008)]. A challenging feature of the expected solitons is their strong inherent anisotropy due to the necessary in-plane orientation of the local moments in the dipolar gas. This may be the first chance of making multidimensional matter-wave solitons, as well as solitons featuring the anistropy due to their intrinsic dynamics. Our analysis is based on the extended Gross-Pitaevskii equation, which includes three-body losses and noise in the scattering length, induced by fluctuations of currents inducing the necessary magnetic fields, which are factors crucial to the adequate description of experimental conditions. By means of systematic three-dimensional (3D) simulations, we find a ramping scenario for the change of the scattering length and trap frequencies which results in the creation of robust solitons, that readily withstand the concomitant excitation of the condensate.

We show that a composite-field (diatom) Goldstone state is expected in a dilute Bose gas for temperatures between the Bose gas critical temperature where the atom Bose-Einstein condensate appears and the temperature where superfluidity sets in. The presence of superfluidity is tied to the existence of a U(1) charge-two diatom condensate in the system. By promoting the global U(1) symmetry of the theory to a gauge symmetry, we find that the mass of the gauge particle generated through the Anderson-Higgs mechanism is related to the superfluid density via the Meissner effect, and the superfluid density is related to the square of the anomalous density in the Bose system.

To overcome the difficulties in defining pressure for a gas confined in an inhomogeneous trap, we define single macroscopic parameters that behave like pressure and volume. We measure the phase diagram of a ${}^{87}$Rb Bose gas in a harmonic trap in terms of those macroscopic parameters obtained from the spatial distribution of atoms. Considering the relevant variables such as the trap potential $\mathcal{V}={\left({\omega }_x{\omega }_y{\omega }_z\right)}^{-1}$, number of atoms $N$, and temperature $T$, a parameter $\Pi =\Pi (N,\mathcal{V},T)$ is introduced to characterize the overall macroscopic pressure of the system. We construct the phase diagram ($\Pi$ vs $T$) identifying the main features related to the Bose-Einstein condensation (BEC) transition in a trapped gas. A thermodynamic description of the phase transition based on purely macroscopic parameters provides us with a description that does not need the local-density approximation. This procedure can be used to explore different aspects related to BEC such as the nature of the phase transition in a trapped gas.

We investigate the ground state of a uniform two-dimensional polarized Fermi gas with Rashba spin-orbit coupling at zero temperature. We construct the phase diagram by comparing the thermodynamic potential of superfluid and phase-separated states in detail. Due to the competition between polarization and spin-orbit coupling, we find that phase-separated states in the phase diagram can be topologically trivial and nontrivial. These two topologically distinct phase-separated states can not be connected without topological phase transition. The spin-orbit coupling reduces the effect of the population imbalance. Therefore, the phase-separated states are unstable to the superfluid phases for a large spin-orbit coupling.

We study dynamical recurrences of a Bose-Einstein condensate in an optical crystal subject to a periodic external driving force. The recurrence behavior of the condensate is analyzed as a function of time close to nonlinear resonances occurring in the classical counterpart. Our mathematical formalism for the recurrence time scales is presented as delicate recurrences, which take place, for instance, when the lattice is perturbed weakly and robust recurrences, which may manifest themselves for a sufficiently strong external driving force. The analysis not only is valid for a dilute condensate, but also is applicable for the strongly interacting homogeneous condensate provided; the external modulation causes no significant change in the density profile of the condensate. We explain the parametric dependence of the dynamical recurrence times, which can easily be realized in laboratory experiments. In addition, we find good agreement between the obtained analytical results and the numerical calculations.

We study high-order harmonic generation from a laser-produced tin plasma using 780 and 390 nm, 40 fs, 1 kHz pulses. Varying the chirp of the laser radiation, we observe variation of the harmonic frequency and intensity. The enhanced 16th and 17th harmonics are attributed to the influence of the strong ionic transitions of tin. Theoretical calculations of the photoabsorption spectra reveal the decisive role of Sn ii and Sn iii transitions in the enhancement of single harmonics. Varying the fundamental frequency we study numerically the spectral width where the harmonic is enhanced. We find, both theoretically and experimentally, that this width is wider than the one of the corresponding resonance in the photoabsorption spectrum. The resonance line modification can be explained by the Stark shift of the autoionizing state in the laser field, as well as the photoionization of this state.

The dynamical behavior of a coupled cavity array is investigated when each cavity contains a three-level atom. For the uniform and staggered intercavity hopping, the whole system Hamiltonian can be analytically diagonalized in the subspace of single-atom excitation. The quantum-state transfer along the cavities is analyzed in detail for distinct regimes of parameters, and some interesting phenomena including binary transmission and selective localization of the excitation population are revealed. We demonstrate that the uniform coupling is more suitable for the quantum-state transfer. It is shown that the initial state of polariton located in the first cavity is crucial to the transmission fidelity, and the local entanglement depresses the state transfer probability. Exploiting the metastable state, the distance of the quantum-state transfer can be much longer than that of Jaynes-Cummings-Hubbard model. A higher transmission probability and longer distance can be achieved by employing a class of initial encodings and final decodings.

We show how to capture a single photon of arbitrary temporal shape with one atom coupled to an optical cavity. Our model applies to Raman transitions in three-level atoms with one branch of the transition controlled by a (classical) laser pulse, and the other coupled to the cavity. Photons impinging on the cavity normally exhibit partial reflection, transmission, and/or absorption by the atom. Only a control pulse of suitable temporal shape ensures impedance matching throughout the pulse, which is necessary for complete state mapping from photon to atom. For most possible photon shapes, we derive an unambiguous analytic expression for the shape of this control pulse, and we discuss how this relates to a quantum memory.

The resonant-state expansion (RSE), a rigorous perturbation theory of the Brillouin-Wigner type recently developed in electrodynamics[E. A. Muljarov, W. Langbein, and R. Zimmermann, Europhys. Lett. 92, 50010 (2010)], is applied to planar, effectively one-dimensional optical systems, such as layered dielectric slabs and Bragg reflector microcavities. It is demonstrated that the RSE converges with a power law in the basis size. Algorithms for error estimation and their reduction by extrapolation are presented and evaluated. Complex eigenfrequencies, electromagnetic fields, and the Green's function of a selection of optical systems are calculated, as well as the observable transmission spectra. In particular, we find that for a Bragg-mirror microcavity, which has sharp resonances in the spectrum, the transmission calculated using the RSE reproduces the result of the transfer- or scattering-matrix method.