In this article we use the method of shortcuts to adiabaticity to design a photonic lattice (array of waveguides) which can drive the input light to a controlled location at the output. The output position in the array is determined by functions of the propagation distance along the waveguides, which modulate the lattice characteristics (index of refraction, and first- and second-neighbor couplings). The proposed coupler is expected to possess the robustness properties of the design method, coming from its adiabatic nature, and also to have a smaller footprint than purely adiabatic couplers. The present work provides a very interesting example where methods from quantum control can be exploited to design lattices with desired input-output properties.

A general theory is presented to describe optomechanical interactions of acoustic phonons, having extremely long lifetimes in superfluid ${}^4\mathrm{He}$, with optical photons in the medium placed in a suitable electromagnetic cavity. The acoustic nonlinearity in the fluid motion is included to consider processes beyond the usual linear process involving the absorption or emission of one phonon at a time. We first apply our formulation to the simplest one-phonon process involving the usual resonant anti-Stokes upconversion of an incident optical mode. However, when the allowed optical cavity modes are such that there is no single-phonon mode in the superfluid, which can give rise to a resonant allowed anti-Stokes mode, we must consider the possibility of two-phonon upconversion. For such a case, we show that the two-step two-phonon process could be dominant. We present arguments for a large two-step process and negligible single-step two-phonon contribution. The two-step process also shows interesting quantum interference among different transition pathways.

I utilize effective field theory(EFT) techniques to calculate the Casimir torque on a cylindrical gear in the presence of a polarizable but neutral object and present results for the energy and torque as a function of angle for a gear with multiple cogs, as well as for the case of a concentric cylindrical gear.

Vibrational noise is one of the most important noises that limits the performance of the nonisotopes atom-interferometers (AIs) -based weak-equivalence-principle (WEP) -test experiment. By analyzing the vibration-induced phases, we find that, although the induced phases are not completely common, their ratio is always a constant at every experimental data point, which is not fully utilized in the traditional elliptic curve-fitting method. From this point, we propose a strategy that can greatly suppress the vibration-induced phase noise by stabilizing the Raman laser frequencies at high precision and controlling the scanning-phase ratio. The noise rejection ratio can be as high as ${10}^{15}$ with arbitrary dual-species AIs. Our method provides a Lissajous curve, and the shape of the curve indicates the breakdown of the weak-equivalence-principle signal. Then we manage to derive an estimator for the differential phase of the Lissajous curve. This strategy could be helpful in extending the candidates of atomic species for high-precision AIs-based WEP-test experiments.

We experimentally study two quantum phase transitions in a sodium spinor condensate immersed in a microwave dressing field. We also demonstrate that many previously unexplored regions in the phase diagram of spinor condensates can be investigated by adiabatically tuning the microwave field across one of the two quantum phase transitions. This method overcomes two major experimental challenges associated with some widely used methods, and is applicable to other atomic species. Agreements between our data and the mean-field theory for spinor Bose gases are also discussed.

We explore the effects of continuous number density measurement on atoms in an optical lattice. By integrating a master equation for quantum observables, we calculate how single-particle correlations decay. We consider weakly and strongly interacting bosons and noninteracting fermions. Even in the Mott regime, such measurements destroy correlations and increase the average energy, as long as some hopping is allowed. We explore the role of spatial resolution and find that the heating rate is proportional to the amount of information gained from such measurements.

An optical parametric amplifier pumped by a Bessel beam is investigated. It is revealed that under propagation in a nonlinear crystal, the signal angular profile after a transient process does not depend on the input profile and the signal beam becomes localized in the pump field. The control of the output signal angular profile by variation of the pump cone angle and intensity is demonstrated. The effect is elucidated by the numerical simulations as well as experiment. The explanation by the derived eigenvalue problem is given.

It is shown by particle-in-cell simulations that powerful terahertz (THz) radiation can be generated by picosecond (ps) laser pulses below ${10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ via a two-color laser scheme. At such laser intensities, increasing the laser duration can result in significant enhancement in THz intensities. From 0.03 ps to 0.9 ps the enhancement climbs to nearly $40\times$ before saturating until 2 ps. This demonstrates that low intensity, readily available ps laser technology could be utilized for driving powerful THz sources. By contrast, for laser intensities high enough to completely ionize the gas medium, it is found that the THz emission decreases with increasing pulse duration: optimal conversion is found for few-femtosecond drivers.

For partially polarized three-dimensional electromagnetic fields, the polarization state is usually expressed in terms of nine generalized Stokes parameters, the coefficients of the nine Gell-Mann matrices in the expansion of the coherency matrix. We consider fully polarized fields, for which the Jones vector for the polarization state can be expressed in terms of five real parameters. Relationships between these five parameters and the nine generalized Stokes parameters are derived. For partially polarized three-dimensional fields there are four additional parameters that describe the partial polarization, two that specify the degree of polarization, and two that specify its orientation.

We present details and expand on the framework leading to the recently introduced degenerate adiabatic perturbation theory [Phys. Rev. Lett. 104, 170406 (2010)], and on the formulation of the degenerate adiabatic theorem, along with its necessary and sufficient conditions [given in Phys. Rev. A 85, 062111 (2012)]. We start with the adiabatic approximation for degenerate Hamiltonians that paves the way to a clear and rigorous statement of the associated degenerate adiabatic theorem, where the non-Abelian geometric phase (Wilczek-Zee phase) plays a central role to its quantitative formulation. We then describe the degenerate adiabatic perturbation theory, whose zeroth-order term is the degenerate adiabatic approximation, in its full generality. The parameter in the perturbative power-series expansion of the time-dependent wave function is directly associated to the inverse of the time it takes to drive the system from its initial to its final state. With the aid of the degenerate adiabatic perturbation theory we obtain rigorous necessary and sufficient conditions for the validity of the adiabatic theorem of quantum mechanics. Finally, to illustrate the power and wide scope of the methodology, we apply the framework to a degenerate Hamiltonian, whose closed-form time-dependent wave function is derived exactly, and also to other nonexactly solvable Hamiltonians whose solutions are numerically computed.

Local randomization is a preprocessing procedure in which one of the legitimate parties of a quantum key distribution (QKD) scheme adds noise to their version of the key and was found by Kraus et al. [Phys. Rev. Lett. 95, 080501 (2005)] to improve the security of certain QKD protocols. In this article, the improvement yielded by local randomization is derived for an imperfect implementation of the Bennett-Brassard 1984 (BB84) QKD protocol, in which the source emits four given but arbitrary pure states and the detector performs arbitrarily aligned measurements. Specifically, this is achieved by modifying an approach to analyzing the security of imperfect variants of the BB84 protocol against collective attacks, introduced in [Phys. Rev. A 88, 012331 (2013)], to include the additional preprocessing step. The previously known improvement to the threshold channel noise, from 11% to 12.41%, is recovered in the special case of an ideal BB84 implementation and becomes more pronounced in the case of a nonideal source. Finally, the bound derived for the asymptotic key rate, both with and without local randomization, is shown to be tight with the particular source characterization used. This is demonstrated by the explicit construction of a family of source states and optimal attacks for which the key-rate bound is attained with equality.

An accurate determination of the effective electric field $\left(E_{\mathrm{eff}}\right)$ in YbF is important as it can be combined with the results of future experiments to give an improved new limit for the electric dipole moment of the electron. We report a relativistic coupled-cluster calculation of this quantity in which all the core electrons were excited. It surpasses the approximations made in the previous reported calculations. We obtain a value of 23.1 GV/cm for $E_{\mathrm{eff}}$ in YbF with an estimated error of less than 10%. The crucial roles of the basis sets and the core excitations in our paper are discussed.

We have investigated the high-order above-threshold ionization (HATI) spectrum of formic acid by means of high-resolution electron spectroscopy using 800-nm femtosecond laser light. The resonance-like enhancement structures in the HATI spectrum are shown to be experimentally reproducible and three enhancement-suppression patterns are observed in different energy regimes with increasing laser intensity. We simulated these patterns successfully by computing the exact solution of time-dependent Schrödinger equation based on the simple hydrogen-like atom, subject to a time-dependent high-intensity laser pulse. The agreement between experiment and theory shows that “channel closing” effects play an important role in the observed resonance-like enhancements (RLEs). The existence of the RLEs for formic acid, which lacks any symmetry, shows that molecular symmetry does not affect the RLEs.

The ability to produce liter volumes of highly-spin-polarized ${}^{129}\mathrm{Xe}$ enables a wide range of investigations, most notably in the fields of materials science and biomedical magnetic resonance imaging. However, for nearly all polarizers built to date, both peak ${}^{129}\mathrm{Xe}$ polarization and the rate at which it is produced fall far below those predicted by the standard model of Rb metal vapor, spin-exchange optical pumping (SEOP). In this work we comprehensively characterized a high-volume flow-through ${}^{129}\mathrm{Xe}$ polarizer using three different SEOP cells with internal volumes of 100, 200, and $300{\mathrm{cm}}^3$ and two types of optical sources: a broad-spectrum 111-W laser [full width at half maximum (FWHM) equal to 1.92 nm] and a line-narrowed 71-W laser (FWHM equal to 0.39 nm). By measuring ${}^{129}\mathrm{Xe}$ polarization as a function of gas flow rate, we extracted the peak polarization and polarization production rate across a wide range of laser absorption levels. Peak polarization for all cells consistently remained a factor of 2–3 times lower than predicted at all absorption levels. Moreover, although production rates increased with laser absorption, they did so much more slowly than predicted by the standard theoretical model and basic spin-exchange efficiency arguments. Underperformance was most notable in the smallest optical cells. We propose that all these systematic deviations from theory can be explained by invoking the presence of paramagnetic Rb clusters within the vapor. Cluster formation within saturated alkali-metal vapors is well established and their interaction with resonant laser light was recently shown to create plasmalike conditions. Such cluster systems cause both Rb and ${}^{129}\mathrm{Xe}$ depolarization, as well as excess photon scattering. These effects were incorporated into the SEOP model by assuming that clusters are activated in proportion to excited-state Rb number density and by further estimating physically reasonable values for the nanocluster-induced velocity-averaged spin-destruction cross section for Rb $(\langle {\sigma }_{\text{cluster-Rb}}v\rangle \approx 4\times {10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1})$, the ${}^{129}\mathrm{Xe}$ relaxation cross section $(\langle {\sigma }_{\text{cluster-Xe}}v\rangle \approx 4\times {10}^{-13}{\mathrm{cm}}^3{\mathrm{s}}^{-1})$, and a non-wavelength-specific photon-scattering cross section $({\sigma }_{\mathrm{cluster}}\approx 1\times {10}^{-12}{\mathrm{cm}}^2)$. The resulting modified SEOP model now closely matches experimental observations.

We study two-center electron interference in molecular photoionization processes by intense attosecond circularly polarized extreme ultraviolet (XUV) laser pulses in both symmetric ${\mathrm{H}}_2{}^{+}$ and nonsymmetric $\mathrm{H}{\mathrm{He}}^{2+}$ one-electron diatomic systems. Simulations from numerical solutions of time-dependent Schrödinger equations for the oriented symmetric molecular ion ${\mathrm{H}}_2{}^{+}$ exhibit a signature of interference with double peaks (minima) in molecular attosecond photoelectron energy spectra (MAPES) at critical angles ${\vartheta }_c$ between the continuum electron momentum ${\mathbf{p}}_e$ and the molecular internuclear $\mathbf{R}$ axis. The interference patterns are shown to be influenced by the molecular Coulomb potential, leading to a shift of the critical angle ${\vartheta }_c$. Dependence of the two-center interference on the pulse ellipticity is also investigated. Furthermore, it is found that the interference phenomena are critically sensitive to the molecular orbital symmetry. For the nonsymmetric molecular ion $\mathrm{H}{\mathrm{He}}^{2+}$, such double peaks in MAPES also occur, thus suggesting a method for imaging orbitals in molecules by intense ultrashort circularly polarized XUV pulses on the attosecond time scale.

We present here a detailed study of the influence of the transverse motion of the atoms in a free-fall gravimeter. By implementing Raman selection in the horizontal directions at the beginning of the atoms' free fall, we characterize the effective velocity distribution, i.e., the velocity distribution of the detected atom, as a function of the laser cooling and trapping parameters. In particular, we show that the response of the detection induces a pronounced asymmetry of this effective velocity distribution that depends not only on the imbalance between molasses beams but also on the initial position of the displaced atomic sample. This convolution with the detection has a strong influence on the averaging of the bias due to Coriolis acceleration. The present study allows a fairly good understanding of results previously published in [New J. Phys. 13, 065025 (2011)], where the mean phase shift due to Coriolis acceleration was found to have a sign different from that expected.

The dynamics of a matter-wave soliton bouncing on the reflecting surface (atomic mirror) under the effect of gravity has been studied by analytical and numerical means. The analytical description is based on the variational approach. Resonant oscillations of the soliton's center of mass and width, induced by appropriate modulation of the atomic scattering length and the slope of the linear potential, are analyzed. In numerical experiments we observe the Fermi-type acceleration of the soliton when the vertical position of the reflecting surface is periodically varied in time. Analytical predictions are compared to the results of numerical simulations of the Gross-Pitaevskii equation and qualitative agreement between them is found.

We study the quantum phases of a Bose-Hubbard model with staggered magnetic flux in two dimensions, as was realized recently [M. Aidelsburger, M. Atala, M. Lohse, J. T. Barreiro, B. Paredes, and I. Bloch, Phys. Rev. Lett. 107, 255301 (2011)]. Within mean-field theory, we show how the structure of the condensates evolves from the weak- to the strong-coupling limit, exhibiting a tricritical point at the Mott-superfluid transition. Nontrivial topological structures (Dirac points) in the quasiparticle (hole) excitations in the Mott state are found within random phase approximation and we discuss how interaction modifies their structures. The excitation gap in the Mott state closes at different $\mathbf{k}$ points when approaching the superfluid states, which is consistent with the findings of mean-field theory.

We show how two frequency combs ${\mathcal{E}}_1$, ${\mathcal{E}}_2$ can be used to measure single-photon, two-photon absorption (TPA), and Raman resonances in a molecule with three electronic bands, by detecting the radio frequency modulation of the nonlinear transmission signal. Some peaks are independent of the carrier frequency of the comb and others shift with that frequency and have a width close to the comb width. TPA and Raman resonances independent of the carrier frequency are selected by measuring the transmission signal $\sim {\mathcal{E}}_1^2{\mathcal{E}}_2^2$ and the single-photon resonances are selected by measuring the transmission signal $\sim {\mathcal{E}}_1^3{\mathcal{E}}_2$. Sinusoidal spectral phase shaping strongly affects the TPA, but not the Raman resonances.