A constraint for applications of multipass cells is their intensive intermirror alignments. This paper reports a compact and robust design for a chaotic multipass cell without any intermirror alignments. In this design the quasichaotic ray dynamics is used to generate multiple long optical paths in a closed system. The quasichaotic cavity can effectively focus the beam when light bounces repeatedly off the cavity surfaces, resulting in a negative beam divergence rate. We demonstrate our mechanism for the two-dimensionally deformed quadrupolar cavity and find a variety of optical paths up to $15.5\text{meter}$ with limited beam divergence in a $68{\mathrm{cm}}^3$ cavity volume.

We demonstrate tunable, extremely blueshifted continuum in $\lambda =1.055\mu \mathrm{m}$ ultrashort laser pulse filamentation in silica. Close to threshold, the continuum appears as a single, isolated blue peak. The spectral position of the two supercontinuum components can be tuned and a regime with encompassing fundamental and second harmonic is possible to achieve. At higher energies, the continuum expands in bandwidth starting from the blue peak. The spectral dynamics and tunability are explained in terms of $X$-wave generation and intrafilament pulse splitting which may be controlled by modifying the input pulse focusing conditions.

We study ultrashort laser-pulse propagation and filamentation dynamics in dispersive Kerr media. We identify the regime for which the filamentation threshold $\left(P_{\mathrm{th}}\right)$ is considerably higher than the critical power $\left(P_{\mathrm{cr}}\right)$ for monochromatic beam collapse in pure Kerr media. In particular, we compare the threshold for the formation of filaments with that for the formation of $\mathsf{X}$-waves. At powers $P_{\mathrm{cr}}<P<P_{\mathrm{th}}$, self-focusing is arrested by group-velocity dispersion, and no filaments or $\mathsf{X}$-waves are formed. At $P⩾P_{\mathrm{th}}$, we observe $\mathsf{X}$-wave formation and a weak filamentation regime. At $P⪢P_{\mathrm{th}}$, we observe both $\mathsf{X}$-waves and fully formed filaments.

The internal one-particle density matrix is discussed for Bose-Einstein condensates with a finite number of particles in a harmonic trap. It is found that the outcome of the diagonalization of the single-particle density matrix depends on the choice of the internal coordinates: The Pethick-Pitaevskii (PP) type of internal density matrix, whose analytical eigenvalues and eigenfunctions are evaluated, yields a fragmented condensate, while the Jacobi type of internal density matrix leads to an ideal condensate. We give a criterion for the choice of the internal coordinates: In the macroscopic limit the internal density matrix should have the same eigenvalues and eigenfunctions as those of the corresponding ideal Bose-Einstein condensate in the laboratory frame, this being a very physical condition. One choice satisfying this boundary condition is given by the internal Jacobi coordinates, while the internal coordinates with respect to the center of mass of the PP density matrix do not satisfy this condition. Based on our criterion, a general definition of the internal one-particle density matrix is presented in a self-bound system consisting of interacting bosons.

In this paper we study the nonlocal properties of two-qubit Werner states parametrized by the visibility parameter $0⩽p⩽1$. A family of Bell inequalities is constructed that proves the two-qubit Werner states to be nonlocal for the parameter range $0.7056<p⩽1$. This is slightly wider than the range $0.7071<p⩽1$, corresponding to the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality. This answers a question posed by Gisin in the positive, i.e., there exist Bell inequalities which are more efficient than the CHSH inequality in the sense that they are violated by a wider range of two-qubit Werner states.

The optical quantum computer is one of the few experimental systems to have demonstrated small scale quantum information processing. Making use of cavity quantum electrodynamics approaches to operator measurements, we detail an optical network for the deterministic preparation of arbitrarily large two-dimensional cluster states. We show that this network can form the basis of a large scale deterministic optical quantum computer that can be fabricated entirely on chip.

We analyze the finite-size corrections to entanglement in quantum critical systems. By using conformal symmetry and density functional theory, we discuss the structure of the finite-size contributions to a general measure of ground state entanglement, which are ruled by the central charge of the underlying conformal field theory. More generally, we show that all conformal towers formed by an infinite number of excited states (as the size of the system $L\to \infty$) exhibit a unique pattern of entanglement, which differ only at leading order ${(1∕L)}^2$. In this case, entanglement is also shown to obey a universal structure, given by the anomalous dimensions of the primary operators of the theory. As an illustration, we discuss the behavior of pairwise entanglement for the eigenspectrum of the spin-$1∕2$ $XXZ$ chain with an arbitrary length $L$ for both periodic and twisted boundary conditions.

We address the problem of unambiguously identifying the state of a probe qudit with the state of one of $d$ reference qudits. The $d$ reference states are assumed pure and linearly independent but we have no knowledge of them. The state of the probe qudit is assumed to coincide equally likely with either one of the $d$ unknown reference states. We derive the optimum measurement strategy that maximizes the success probability of unambiguous identification and find that the optimum strategy is a generalized measurement. We give both the measurement operators and the optimum success probability explicitly. Technically, the problem we solve amounts to the optimum unambiguous discrimination of $d$ known mixed quantum states.

We present a laser-microwave double-resonance technique for the precise determination of $g$ factors in heavy, highly charged ions confined in a Penning trap. This technique allows one to probe the microwave transitions between the Zeeman sublevels of hyperfine states by the optical fluorescence from the corresponding hyperfine transition and thus yields a possibility to measure $g_F$ factors in a laser spectroscopy experiment. A combination of measured $g_F$ factors and the hyperfine transition frequency allows one to simultaneously determine the electronic $g$ factor $g_J$ and the nuclear $g$ factor $g_I$ from one experiment. Thus, we introduce a stringent test of corresponding calculations in the framework of bound-state quantum electrodynamics and a possibility to determine nuclear magnetic moments in the absence of diamagnetic shielding.

We report on the buffer-gas cooling and trapping of CrH and MnH molecules in a magnetic quadrupole trap with densities on the order of ${10}^6{\mathrm{cm}}^{-3}$ at a temperature of $650\mathrm{mK}$. Storage times of up to $180\mathrm{ms}$ have been observed, corresponding to a 20-fold lifetime enhancement with respect to the field-free diffusion through the ${}^3\mathrm{He}$ buffer-gas. Using Monte Carlo trajectory simulations, inelastic molecule-${}^3\mathrm{He}$ collision cross sections of $1.6\times {10}^{-18}$ and $3.1\times {10}^{-17}{\mathrm{cm}}^2$ are extracted for CrH and MnH, respectively. Furthermore, elastic molecule-${}^3\mathrm{He}$ collision cross sections of $1.4(\pm 0.5)\times {10}^{-14}{\mathrm{cm}}^2$ are determined for both species. We conclude that the confinement time of these molecules in a magnetic trapping field is limited by inelastic collisions with the helium atoms leading to Zeeman relaxation.

We have developed a theoretical description of the evolution of ground state coherences between magnetic sublevels in Rb vapor in the presence of a magnetic field along an arbitrary direction. This formalism uses a rotation matrix approach to describe the evolution of coherences created by two traveling wave laser pulses with orthogonal polarizations. The effect of a magnetic field can be described as a time-dependent rotation of the atomic system about the quantization axis. Predictions based on this theoretical formalism for the functional form of Larmor oscillations in a magnetic field are studied using a coherent transient effect known as magnetic grating free induction decay (MGFID) using room temperature vapor and laser cooled atoms. We find the theoretical predictions to be in excellent agreement with data. The velocity distribution of the cold sample measured from the dephasing time of the MGFID in the absence of magnetic fields is in agreement with the sample temperature obtained by imaging the ballistic expansion of the trapped cloud. By using rate equations to model atomic coherences, it is also possible to predict the evolution of magnetic grating echoes (MGE) in a magnetic field. We compare these predictions with experiments from cold atoms and discuss applications of the MGFID and MGE that relate to a precision measurement of the atomic $g$ factor ratio using ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ isotopes.

We measured the $L$ x-ray intensities of Pb, Au, and W for several different azimuthal angles and partially polarized photon beams by using high-purity low-energy Ge detectors. We utilized a monochromatized synchrotron beam as the source. It had an energy of $10.88–40\mathrm{keV}$, and its degree of linear polarization $P$ ranged from 0.84 to 0.89. The scattering polar angle $\left(\theta \right)$ was 90°, and the azimuthal angle $\left({\varphi }_1\right)$ was 0° or 90°, relative to the polarization direction. We obtained the x-ray intensity ratio $R[=I({\varphi }_1=0°)∕I({\varphi }_1=90°)]$. We observed that the $Ll$ intensities depended on the azimuthal scattering angle ${\varphi }_1$, i.e., $R=0.92–0.94$, 0.91–0.94, and 0.90–0.93 for Pb, Au, and W, respectively. On the other hand, the dependence of $L\alpha$ on the azimuthal scattering angle was not clear due to experimental uncertainty. The anisotropy of $L\gamma$ was not observed. These results agreed with the theoretical calculations based on Scofield’s theory.

We observed the thermal phonon resonance of nitrogen gas with optical-beating Brillouin scattering and measured the sound velocity and the absorption coefficient in the MHz region. Optical-beating spectroscopy possesses a frequency resolution of $1\mathrm{kHz}$, which enabled us to resolve the fine structure of the thermal phonon resonance spectra. Resonance peaks of phonons were observed at every $185\mathrm{kHz}$ in the resonance cavity composed of two flat glass plates. The measurement accuracy of the sound velocity and the absorption coefficient was remarkably improved to ${10}^{-4}$ and ${10}^{-1}$, respectively.

The purpose of this Comment is to show that we find that the conclusions presented in a paper by Nair and Vijaya [Phys. Rev. A 76, 053805 (2007)], concerning the perfect periodic ordering of self-assembled photonic crystals, are not supported and contradict previous studies of this matter.

In this Reply, we show that the authors of the preceding Comment have not contested any of the major results presented in our original paper [R. V. Nair and R. Vijaya, Phys. Rev. A 76, 053805 (2007)], since the defects have not been quantified in their calculations and the extinction may also arise from factors other than those mentioned in the Comment.

We describe three-body collisions close to a Feshbach resonance by taking into account two-body scattering processes involving both the open and the closed channels. We extract the atom-dimer scattering length and the three-body recombination rate, predicting the existence at negative scattering length of a sharp minimum in the recombination losses due to the presence of a shallow bound level. We obtain very good agreement with the experimental results in atomic ${}^{133}\mathrm{Cs}$ of Kraemer et al. [Nature (London) 440, 315 (2006)], and predict the position of Efimov resonances in a gas of ${}^{39}\mathrm{K}$ atoms.

We present theory for the laser-assisted photoelectric effect (LAPE) from metal surfaces in combined extreme ultraviolet attosecond and near-infrared femtosecond pulses. We discuss how LAPE with short pulses is used to make time-resolved measurements. We propose the use of reference states located outside the metal surface to allow for measurements of the absolute travel time of electronic wave packets formed inside the metal and to the surface. Finally, we study the variation in the magnitude of laser-induced sidebands with the length of the laser pulse.

We report on experimental investigations of stimulated Raman adiabatic passage (STIRAP) in a ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ crystal. STIRAP drives complete, coherent population transfer between two hyperfine levels in the ${\mathrm{Pr}}^{3+}$ ions. We investigate the variation of the STIRAP transfer efficiency with the experimental parameters: e.g., detunings, Rabi frequencies, and pulse delays. In addition, we also observe an alternative and efficient, adiabatic transfer process—i.e., $b$-STIRAP—which occurs for a reversed sequence of laser pulses. We compare the efficiencies and time-resolved transfer dynamics of STIRAP and $b$-STIRAP. The experimental data are supported by numerical simulations, also including the effect of laser frequency jitter. Our experimental data and the numerical simulations provide a clear and convincing demonstration of adiabatic excitations in a solid medium.

We study adiabatic population transfer with dephasing in two-level models driven by a chirped driving field. We show that the population transfer is maximized when the dynamics follows specific ellipses as trajectories in the parameter space. We determine the optimal parameters and estimate the losses in a closed form. These estimates show a similar robustness as for the standard lossless adiabatic processes with respect to variations of the parameters.

Generation of extreme ultraviolet supercontinuum in the plateau region of high-order harmonics has been demonstrated by shaping a fundamental-wave laser pulse with its second- and third-harmonic pulses. Such a Fourier synthesis of the optical waveforms could confine the harmonic emissions mainly in the center peak of the driving pulse, which suppresses those on other half-cycles efficiently, and as a consequence avoids or reduces spectral interference of harmonic emissions at different half-cycles, resulting in harmonic emissions free of interference within a certain spectral span in the frequency domain that forms supercontinuum in the high-order harmonic plateau region. This supercontinuum is significant for the efficient generation and further control of single attosecond pulses.