Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L41: Atom-Photon Interactions |
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Sponsoring Units: DAMOP Chair: Pierre Meystre, University of Arizona Room: 413 |
Tuesday, March 17, 2009 2:30PM - 2:42PM |
L41.00001: Few electron systems in a strong laser pulse Nicholas Vence, Predrag Krstic, Robert Harrison We propose a numerical procedure for investigating the dynamics of a one electron wave function in a strong, sub-femtosecond laser field. The non-perturbative time evolution method does not rely on an eigenfunction basis set but uses the multiresolution techniques for spatial discretization as described in [Harrison et. al., J. Chem. Phys. 121, 2866 (2004)]. The time propagation is done by the chin-chen time splitting method [Chin Chen, J. Chem. Phys. 114, 7338 (2001)]. The excitation and ionization cross-sections for the hydrogen atom, the oxygen ion and the hydrogen molecular ion could serve as a benchmark for future calculations and experiments due to the well controlled accuracy inherent in this numerical scheme. [Preview Abstract] |
Tuesday, March 17, 2009 2:42PM - 2:54PM |
L41.00002: Theoretical study of electron momentum distribution in He tunneling ionization Li Guo, Shengsheng Han, Jingyun Fan, Jing Chen The electron scattering amplitude given by the S-matrix theory, up to the third order, can be written as $S_{fi} =-i\int_{-\infty }^\infty dt\left\langle {\psi _{A_f } (p,t)} \right|V_A (t)\left| {\varphi _0 } \right\rangle -i\int_{-\infty }^\infty dt\int_{-\infty }^\infty d{t}'\left\langle {\psi _{A_f } (p,t)} \right|VG_A (t,{t}')V_A ({t}')\left| {\varphi _0 } \right\rangle -i\int_{-\infty }^\infty dt\int_{-\infty }^\infty d{t}'\int_{-\infty }^\infty d{t}''\left\langle {\psi _{A_f } (p,t)} \right|VG_A (t,{t}')VG_A ({t}',{t}'')V_A (t)\left| {\varphi _0 } \right\rangle $, with the first term describing the direct ATI process (that the initial state directly scatters to the final state), the second term describing that the electron initially scatters to the intermediate states via the laser-electron interaction (V$_{A})$ and then scatters to the final state via the electron-ion interaction (V) (a rescattering ATI process), and the third term describing that the electron scatters to the final state via two cascaded ATI processes. All scattering processes are physically indistinguishable, so we assume that all divergence parts in scattering processes (corresponding to the forward scattering) can be absorbed into the first term and exclude them in the calculation, where the divergence is due to the long range Coulomb interaction ($V=-$1$/r)$. We apply this method to study the He ionization and our theoretical results are qualitatively consistent with recent experimental observations. [Preview Abstract] |
Tuesday, March 17, 2009 2:54PM - 3:06PM |
L41.00003: Modulation of molecular high harmonic generation by electron de Broglie wave interference Jing Chen, Jingyun Fan In the intense laser field, the amplitude for the $n^{th}$-order high harmonic generation (HHG) of a two-center molecule using the modified Lewenstein model is written as $S(n)\propto \sum\limits_{l,m} {\vert (e^{i\vec {k}'\cdot \vec {R}/2}-e^{-i\vec {k}'\cdot \vec {R}/2})\Phi _i (\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {k}} ')\vert ^2J_l (-\frac{\vec {k}\cdot \vec {A}_0 }{\omega })J_m (\frac{\vec {k}\cdot \vec {A}_0 }{\omega })} $, where $m $and $l $are number of photons that the electron absorbs/emits at ionization /recombination and are restricted by the energy conservation, $n=(m\pm 1)+l$. The electron's kinetic energy is related to photon number $m$ and molecular ionization potential $I_p $ as $\vec {k}^{\mbox{2}}\mbox{/2 }=\mbox{ (}m\mbox{ }\pm 1)\omega -I_p $. $\vec {k}'$ is parallel to $\vec {k}$with $\vec {k}'^2/2=\vec {k}^2/2+I_p $ due to the bound potential acceleration effect in the recapture. $J_l ()$ is $l^{th}$ order Bessel function and $\Phi _{i}(k)$ is the amplitude of electron momentum state (Fourier transformation of the atomic wavefunction \textit{$\varphi $}$_{i}$ in the LCAO-MO approximation). Clearly MHHG at each order ($n^{th})$ is contributed by a number of momentum states, being a summation of interferences $(e^{i\vec {k}'\cdot \vec {R}/2}-e^{-i\vec {k}'\cdot \vec {R}/2})$ weighed by state probabilities which is affected by laser parameters. We numerically evaluate the MHHG spectra for different laser intensities and various alignment angles, the results are consistent with recent experimental observations. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:18PM |
L41.00004: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 3:18PM - 3:30PM |
L41.00005: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 3:30PM - 3:42PM |
L41.00006: Entangling photons by means of the nonlinear response of quantum wells to an ultrashort pulse Mikhail Erementchouk, Michael Leuenberger Polarization-entangled photons can be produced from semiconductor bulk crystals made of CuCl through resonant hyperparametric scattering off the bound biexciton state with a yield exceeding $10^{-5}$, much higher than yields $<10^{-9}$ achieved with bulk nonlinear crystals. Here we show a different method to produce pairs of entangled photons in the short time response of a quantum well excited by a short intense pulse. At the time scales, where the biexciton effect is not yet pronounced, the Pauli exclusion principle is responsible for many-body correlations among excitons, giving rise to the production of entangled photons with a yield of around $10^ {-2}$. We make use of a quantum-field theoretical two-particle density matrix to calculate the entanglement for arbitrary emission angles of the entangled pairs of photons. At the time scales, where the heavy-light hole splitting is resolved, the resonances corresponding to different two-exciton states are developing, so that a simple kinematic theory can be presented, which relates the states of the outgoing photons with the respective two-exciton states. We study remarkably strong nontrivial dependence of entanglement on the emission angles of the entangled photons and on the ellipticity parameters of the incident photons. We show that the emitted entangled 2-photon states are always in a triplet state. [Preview Abstract] |
Tuesday, March 17, 2009 3:42PM - 3:54PM |
L41.00007: Two and three dimensional study of the hydrogen molecular ion H2+ confined between double boxes of spheroidal and spherical geometries. Martin Molinar, German Campoy Considering first a two-dimensional system, we study the hydrogen molecular ion confined in the space between two ellipses, and then we consider its confinement in the space between two prolate spheroids. In the Born -- Oppenheimer approximation, we solve numerically the Schrodinger's equation for the above mentioned cases, using an algorithm that allows us to calculate the energies for different given values of the confinement parameters. We also consider the confinement in the region limited by two concentric circumferences and in the three-dimensional case, in the region between two concentric spherical shells. In the last two cases we use the variational method in order to estimate the energy of the ground state. Some properties of the system as the pressure exerted by the confinement, the polarizability in the approximations of Kirkwood and Buckingham and the energies of the vibrational states are calculated. The behavior of the internuclear separation is analyzed for all the geometries considered. [Preview Abstract] |
Tuesday, March 17, 2009 3:54PM - 4:06PM |
L41.00008: Dipole in a Magnetic Field, Work, and Quantum Spin Robert J. Deissler Place an atom in a nonuniform static external magnetic field and, because of the interaction between the atom's magnetic moment and the magnetic field gradient, the atom will accelerate. An important and fundamental question, which has been neglected in the literature, is whether or not the magnetic field is doing work on the atom. It is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the atom's internal energy), whether or not it does work on the electron-spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. If the electron does have a rotational kinetic energy, which is shown to be consistent with the Dirac equation, the acceleration of a silver atom in a Stern-Gerlach experiment or the emission of a photon from an electron spin-flip can be explained without requiring the magnetic field to do work. A classical dipole (a spinning charged ball) is also studied. For details please refer to R.J. Deissler, Phys. Rev. E. {\bf 77}, 036609 (2008). A link to this paper, as well as other information, may be found at http://deissler.us/. [Preview Abstract] |
Tuesday, March 17, 2009 4:06PM - 4:18PM |
L41.00009: Casimir force measurements between a gold sphere and a rectangular corrugated Silicon plate Yiliang Bao, Jie Zou, H.B. Chan The Casimir force is the interaction that results from quantum fluctuations of electromagnetic fields in vacuum and strongly depends on the shape of the boundaries that confines the electromagnetic fields. Most previous experiments involve simple geometries such as plate-sphere, two parallel plates or two cylinders, where the pair-wise summation of two-body interactions is still valid. To demonstrate the strong shape dependence of the Casimir force, we choose one of the interacting surfaces to be an array of trenches with widths ranging from 200 nm to 500 nm. Both high-aspect-ratio trenches with depth of 1 um and shallow trenches with depth of 100 nm are fabricated. The force gradient on these structures is measured with a micromechanical torsional oscillator for the separations between 150 nm and 500 nm. We observe deviations from both the pair-wise additive approximation and the proximity force approximation. The observed deviation, however, is smaller than the calculated values for perfectly conducting surfaces, possibly due to the interplay between finite conductivity and geometry effects. [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L41.00010: Distance dependence of contact potential in cylindrical-plane Casimir force measurements Qun Wei, Kevin Miller, Diego Dalvit, Roberto Onofrio We report on the status of an experiment aimed at measuring the Casimir force in cylinder-plane geometry. In order to characterize the apparatus, we have first performed small distance electrostatic calibrations. This has allowed us to better identify various general issues on the measurement of the Casimir force, such as the distance dependence of the contact potential, and the delicate assessment of the absolute distance. The determination at all distances of the contact potential $V_{0}$ is particularly crucial since its distance dependence can affect the entire data analysis procedure. We also carried on the measurements of $V_{0}$ in sphere-plane and plane-plane geometries for comparison. [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L41.00011: Optical binding force acting on two optically trapped particles H.D. Ou-yang, Ming-Tzo Wei In addition to common optical manipulation setups such as an optical tweezers, the radiation forces generated by a laser can also induce chain-like arrangements of $\mu $m-sized dielectric spheres through coherent multiple scattering, through a process known as optical binding (OB). Although the forces generated through OB are on the order of piconewtons, they are still sufficient to overcome other relevant interactions in the suspension such as Van Der Waals and gravitational forces and Brownian fluctuations. The OB force oscillates from attractive to repulsive as function of interparticle separation; as observed in theoretical models and optical fields found in systems such as counter propagating lasers in dual-beam optical-fibers. Using a dual optical tweezers setup, we have measured the inter-particle OB force from two 1.5 micron diameter polystyrene particles in suspension as a function of their separation by holding them in separate optical traps. Using a calibration scheme, we have isolated the OB force from the background of hydrodynamic and Brownian forces. Using experimental measurements and theoretical predictions, we also proved that by changing the respective polarizations between parallel and perpendicular orientations of the two traps, the OB force was the only force acting on the particles. [Preview Abstract] |
Tuesday, March 17, 2009 4:42PM - 4:54PM |
L41.00012: Reflection of Various Types of Waves by Layered Media Sergiy Mokhov, Boris Zeldovich The one-dimensional wave equation describing propagation and reflection of waves in a layered medium is transformed into an exact first-order system for the amplitudes of coupled counter-propagating waves. Any choice of such amplitudes, out of continuous multitude of them, allows one to get an accurate numerical solution of the reflection problem. We discuss relative advantages of particular choices of amplitude. We also introduce the notion of reflection strength $S$ of a plane wave by a nonabsorbing layer, which is related to the reflection intensity $R$ by $R=\tanh ^2S$. We show that the total reflection strength by a sequence of elements is bounded above by the sum of the constituent strengths, and bounded below by their difference. Reflection strength is discussed for propagating acoustic waves and quantum mechanical waves. We show that the standard Fresnel reflection may be understood in terms of the variable $S$ as a sum or difference of two contributions, one due to a discontinuity in impedance and the other due to a speed discontinuity. [Preview Abstract] |
Tuesday, March 17, 2009 4:54PM - 5:06PM |
L41.00013: Gravitational Redshift and Deflection of Slow Light Justin Dressel, S. Rajeev, John Howell, Andrew Jordan We explore the nature of the classical propagation of light through media with strong frequency-dependent dispersion in the presence of a gravitational field. In the weak field limit, gravity causes a redshift of the optical frequency, which the slow-light medium converts into a spatially-varying index of refraction. This results in the bending of a light ray in the medium. We further propose experimental techniques to amplify and detect the phenomenon using weak value measurements. Independent heuristic and rigorous derivations of this effect are given. [Preview Abstract] |
Tuesday, March 17, 2009 5:06PM - 5:18PM |
L41.00014: Control of a mechanical resonator mode by cavity-enhanced light scattering Ako Chijioke, John Lawall Reaching the quantum regime of a mechanical resonator is facilitated by using a resonator with a small mass and high frequency. On the other hand, optical interferometry fails if the dimensions of the resonator are not significantly larger than the optical wavelength. Here we discuss and demonstrate an alternative optical technique employing scattering losses within an optical cavity to sense the motion of a resonator that can have dimensions well below the optical wavelength. We place a wavelength-scale mechanical resonator at the waist of a high-finesse optical cavity, lock the cavity to a resonance, and monitor the transmission. As the resonator vibrates, it modulates the cavity loss and thereby the transmitted power. We calibrate the sensitivity to resonator position by means of a known static displacement. We then sense the thermal motion of the resonator, and employ active feedback to cool, heat, and stiffen the mechanical mode. [Preview Abstract] |
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