Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session U36: Quantum Optics, Quantum Control, and Ultrafast Processes |
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Sponsoring Units: DAMOP Chair: Bernado Mendoza, CIO, Mexico Room: LACC 510 |
Thursday, March 24, 2005 8:00AM - 8:12AM |
U36.00001: Towards the coupling of microsphere resonators and self-assembled semiconductor quantum dots. Pablo Bianucci, John Robertson, Andreas Muller, Luis Prill Sempere, Chih-Kang Shih Coupling semiconductor quantum dots with microcavities is a challenge which opens the door to many interesting basic and applied experiments. Using microsphere resonators and self-assembled quantum dots has the advantage of allowing mechanical scanning of the resonator position to find a quantum dot in resonance (or far from it). We will show our progress toward that goal, which includes measuring the Q factor of the resonators in different conditions. [Preview Abstract] |
Thursday, March 24, 2005 8:12AM - 8:24AM |
U36.00002: Hoping to get something out of nothing: Searching for hypothetical forces in the Casimir regime Ricardo S. Decca In the first part of this talk our measurements using microelectromechanical systems in the Casimir regime will be discussed. A metrological analysis of these results is used to rule out different models for the expression of the Casimir force at finite temperatures. In the analysis, corrections to the Casimir force were calculated or estimated. These corrections are due to the grain structure of the metal layers (including the variation of optical data and patch potentials), their surface roughness (including nonmultiplicative and diffraction-type effects), and nonlocal effects. In the second part it will be shown how these families of measurements are being used to set more stringent constraints in the search for corrections to the Newtonian gravitational potential. Our latest results and the proposed improvements to obtain better limits will be presented. [Preview Abstract] |
Thursday, March 24, 2005 8:24AM - 8:36AM |
U36.00003: Two-dimensional `photon fluid': Effective photon-photon interaction and physical realizations Susanne Viefers, Jon Magne Leinaas, Thors Hans Hansson, Raymond Chiao We describe a recently developed effective theory for atom-mediated photon-photon interactions in a two-dimensional ``photon fluid'' confined to a Fabry-Perot resonator. The photons in the lowest longitudinal cavity mode will appear as massive bosons interacting via a renormalized delta-function potential with a strength determined by physical parameters such as the density of atoms and the detuning of the photons relative to the resonance frequency of the atoms. We discuss novel quantum phenomena for photons, such as Bose-Einstein condensation and bound state formation, as well as possible experimental scenarios based on Rydberg atoms in a microwave cavity, or alkali atoms in an optical cavity. [Preview Abstract] |
Thursday, March 24, 2005 8:36AM - 8:48AM |
U36.00004: Path Entangled Photons from Parametric Down-Conversion Hagai Eisenberg, Juan Hodelin, George Khoury, Dirk Bouwmeester Path entangled photon states can be used to overcome classical limits on the accuracy of interferometric measurements such as the diffraction limit. These states are superpositions of finding $n$ photons in one out of two (or more) paths. Using stimulated parametric down-conversion (PDC), we propose a method for generating heralded multiphoton path entanglement, without applying post-selection. PDC is relatively easy to produce compared to pure Fock states as demanded by other proposals. By a special coincidence detection at one down-converted arm, the photons of the second arm non-locally bunch into the desired state. Entanglement in photon number is created between two polarization modes rather than two paths. A polarization beam-splitter and a $\lambda $/2 waveplate can translate between the two representations. The experimental generation of a two-photon path entangled state was detected by observing interference at half the photon wavelength. The scheme is generally extendable to higher photon numbers. \newline [1] M.J. Holland and K. Burnett, ``Interferometric detection of optical phase shifts at the Heisenberg limit'', Phys. Rev. Lett. \textbf{71}, 1355 (1993). \newline [2] P. Kok, H. Lee and J.P. Dowling, ``Creation of large-photon-number path entanglement conditioned on photodetection'', Phys. Rev. A \textbf{65}, 052104 (2002). [Preview Abstract] |
Thursday, March 24, 2005 8:48AM - 9:00AM |
U36.00005: Predicting superluminality using Einstein causality David Roundy, Elefterios Lidorikis, Mihai Ibanescu, John D. Joannopoulos We will show that in any system having population inversion and a sufficiently small spontaneous decay rate there exists soliton solutions having superluminal velocities. The existence of these solitons can be proven using Einstein causality in any system where there is gain and a loss mechanism, provided spontaneous emission may be neglected. The shape of these solitons depends on the details of the electronic system, but their existence does not. Although coupling to this soliton by pulses outside the gain material does not appear to be possible, we propose that superluminal pulses may be observed by setting up a ``seed field'' in the system prior to introducing the population inversion. [Preview Abstract] |
Thursday, March 24, 2005 9:00AM - 9:12AM |
U36.00006: Slow Light Using Electromagnetically Induced Transparency from Spin Coherence in [110] Strained Quantum Wells Shu-Wei Chang, Shun-Lien Chuang, Connie J. Chang-Hasnain, Hailin Wang The electromagnetically induced transparency from spin coherence has been proposed in [001] quantum wells recently. [1] The spin coherence is a potential candidate to demonstrate semiconductor-based slow light at room temperature. However, the spin coherence time is not long enough to demonstrate a significant slowdown factor in [001] quantum wells. Further, the required transition of light-hole excitons lies in the absorption of heavy-hole continuum states. The extra dephasing and absorption from these continuum states are drawbacks for slow light. Here, we propose to use [110] strained quantum wells instead of [001] quantum wells. The long spin relaxation time in [110] quantum wells at room temperature, and thus more robust spin coherence, [2] as well as the strain-induced separation [3, 4] of the light-hole exciton transition from the heavy-hole continuum absorption can help to slow down light in quantum wells. [1] T. Li, H. Wang, N. H. Kwong, and R. Binder, Opt. Express 11, 3298 (2003). [2] Y. Ohno, R. Terauchi, T. Adachi, F. Matsukura, and H. Ohno, Phys. Rev. Lett. 83, 4196 (1999). [3] C. Y. P. Chao and S. L. Chuang, Phys. Rev. B 46, 4110 (1992). [4] C. Jagannath, E. S. Koteles, J. Lee, Y. J. Chen, B. S. Elman, and J. Y. Chi, Phys. Rev. B 34, 7027 (1986). [Preview Abstract] |
Thursday, March 24, 2005 9:12AM - 9:24AM |
U36.00007: Optical High Harmonic Generation in $\rm \bf C_{60}$ Guoping Zhang \newcommand{\cm}{$\rm C_{60}$ } \newcommand{\ete}{{\it et al.}} \newcommand{\prl} {Physical Review Letters } \newcommand{\prb} {Physical Review B } High harmonic generation (HHG) requires a strong laser field, but in \cm a relatively weak laser field is sufficient. Numerical results presented here show while its low order harmonics result from the laser field, its high order ones are mainly from the multiple excitations. Since high order harmonics directly correlate electronic transitions, the HHG spectrum accurately measures transition energies. Therefore, \cm is not only a promising material for HHG, but may also present an opportunity to develop HHG into an electronic structure probing tool. References: G. P. Zhang, \prl {\bf 91}, 176801 (2003); G. P. Zhang and T. F. George, \prb {\bf 68}, 165410 (2003); P. B. Corkum, \prl {\bf 71}, 1994 (1993); G. P. Zhang and Thomas F. George, \prl {\bf 93}, 147401 (2004); H. Niikura \ete, Nature {\bf 417}, 917 (2002); {\it ibid.} {\bf 421}, 826 (2003); Y. Mairesse \ete, Science {\bf 302}, 1540 (2003); A. Baltuska \ete, Nature {\bf 421}, 611 (2003). [Preview Abstract] |
Thursday, March 24, 2005 9:24AM - 9:36AM |
U36.00008: Controlling vibrational excitations in $\rm \bf C_{60}$ by laser pulse durations Guoping Zhang, Thomas F. George Two similar off-resonant ultrafast laser experiments [1-3] in $\rm C_{60}$ have reported two different vibrational modes that dominate the relaxation process: one predicts the ag modes while the other the hg modes. A systematic simulation presented here reveals that this experimental discrepancy results from the laser pulse duration. The numerical results show that since each mode $\nu$ has a distinct optimal duration $\tau_o^\nu$, the ag modes are strongly suppressed for durations longer than 40 fs, while the hg modes start to grow. For the off-resonant and low-intensity excitations, the period $\Omega^o_\nu$ of the dominant mode and $\tau_o^\nu$ satisfy the relation $\Omega_\nu^o/{\tau}_o^\nu \approx 3.4$. By carefully scanning the laser frequencies and pulse durations, a comprehensive excitation diagram is constructed, which can be used to guide experiments to selectively excite the ag and hg modes in cm by an ultrafast laser [4,5]. Its potential impact is also discussed. \newcommand{\prl}{{\small \it Phys. Rev. Lett.} } \newcommand{\prb}{{\it Phys. Rev. B} } \newcommand{\et}{{\it et al. }} \newcommand{\ete}{{\it et al.}} [1] S. Dexheimer \ete, {\it Ultrafast Phenomena VIII}, edited by J. L. Martis \ete, {\it Springer Series in Chemical Physics} {\bf 55}, 81 (1993). [2] V. R. Bhardwaj \ete, \prl {\bf 91}, 203004 (2003). [3] H. Hohmann \ete, \prl {\bf 73}, 1919 (1994). [4] G. P. Zhang and T. F. George, \prl {\bf 93}, 147401 (2004). [5] G. P. Zhang, \prl {\bf 91}. 176801 (2003). [Preview Abstract] |
Thursday, March 24, 2005 9:36AM - 9:48AM |
U36.00009: Adaptive engineering of coherent soft-x-rays by temporal and spatial laser-pulse shaping Thomas Pfeifer, Ron Kemmer, Robert Spitzenpfeil, Dominik Walter, Carsten Winterfeldt, Christian Spielmann, Gustav Gerber We demonstrate qualitative amplitude shaping of the coherent soft x-ray spectrum produced in the process of high-harmonic generation. This is accomplished by applying adaptive femtosecond pulse shaping methods. We performed the basic operations of complete spectral control by 1) selective generation of extended parts of the high-harmonic spectra, 2) tunable single harmonic generation and 3) creation of spectral holes (suppression of harmonics) in the plateau region of the spectrum. Our ability to qualitatively ``engineer'' the coherent spectral properties by application of temporal and spatial laser-pulse-shaping methods has immediate consequences for the developing field of attosecond x-ray science. Control over the spectrum is directly related to the control over the attosecond pulse shape as we will show by comparing experiment with simulation. In addition, even more important is the prospect to extend the field of coherent control into the soft x-ray range. In the future, the proposed technique will allow us to directly manipulate electronic motion on its natural attosecond time scale. [Preview Abstract] |
Thursday, March 24, 2005 9:48AM - 10:00AM |
U36.00010: Synchronization of femtosecond laser and electron pulses with sub-ps precision Rick Clinite, Hyuk Park, Xuan Wang, Shouhua Nie, Jim Cao Sub-picosecond synchronization between the pump laser and probe electron pulses is crucial for conducting time-resolved electron diffraction. We have achieved this synchronization with such precision using real-time ultrafast shadow imaging. In this approach we quantitatively monitored the temporal evolution of electron shadow images induced by the transient space-charge field formed near a metal surface in the wake of excitation laser pulses. In principle, this is a universal approach independent of the structural dynamics under investigation and can be applied to a variety of diffraction setups and using laser pulses with different wavelengths. [Preview Abstract] |
Thursday, March 24, 2005 10:00AM - 10:12AM |
U36.00011: Athwart Proton Migration in Polyatomic Molecules during Strong-Field Laser Pulse Dmitri Romanov, Alexei Markevitch, Stanley Smith, Robert Levis Coulomb-explosion fragmentation of large polyatomic molecules caused by strong non-resonant laser field may involve complex motion of constituent protons during ulrashort laser pulse. We compare kinetic energy distributions of H+ ions produced in the Coulomb-explosion dissociation of anthracene, (C$_{14}$H$_{10} $), 1,2,3,4,5,6,7,8-octahydroanthracene, (OHA, C$_{14}$H$_{18} $), and 9,10-anthraquinone, (AQN, C$_{14}$O$_{2}$H$_{8}$), subjected to 60 fs, 800 nm laser pulses of intensity between 0.4 and 4.0×10$^{14}$ W·cm$^{-2}$. The distributions are signatures of the molecular structure effects on the energy coupling and the proton motion over the pulse duration. Most revealing are the curves of the kinetic energy cutoff as a function of the laser intensity: they reflect prolong nonadiabatic charge localization in the molecular ions. The cutoff curve for AQN differs drastically from those for anthracene and OHA, demonstrating much greater saturation value ($\sim$80 eV compared to $\sim$50 eV). The differences are interpreted in terms of proton migration across the electric field on the initial stage of fragmentation process. This migration is caused by nonadiabatic electron dynamics; our model calculations agree with the experimental data. [Preview Abstract] |
Thursday, March 24, 2005 10:12AM - 10:24AM |
U36.00012: Dynamics of Molecular Fragmentation Mediated by Charge-Transfer States Robert Levis(1,*), Dmitri Romanov(2,*), Alexei Markevitch(1,*), Stanley Smith, Dusan Lorencz, Dusan Velic Dissociative ionization of large organic molecules caused by ultrashort strong-field laser pulses is largely predetermined by nonadiabatic electron dynamics during the pulse. The key element of the nonadiabatic process is the bottleneck transition from the system’s ground state to the charge-transfer doorway state of the excited-state manifold. The induced charge transfer across large distances in polyatomic molecules and ions evolves into a complicated dynamics that can include prolong charge localization and sequential ionization. This electron-charge dynamics affects essentially the ensuing nuclear motion and thus determines the fragmentation pattern and charge distribution among the fragments. We observed manifestations of nonadiabatic electron-nuclear dynamics mediated by charge-transfer states in a series of experiments on related polyaromatic molecules, including study of the fragmentation threshold as a function of the laser intensity, the proton kinetic energy distributions, and the relative yield of ionized fragments as a function of the carrier wavelength. In all these cases our model calculations agree quantitatively with the experimental data. [Preview Abstract] |
Thursday, March 24, 2005 10:24AM - 10:36AM |
U36.00013: Phase Coherent Photorefractivity in ZnSe Quantum Wells Suvranta Tripathy, Hans-Peter Wagner, Hans-Peter Tranitz, Wolfgang Langbein We observe an efficient phase coherent photorefractive (PCP) effect in ZnSe single quantum wells for ultra short light pulses resonant to the excitonic transition. The effect has been investigated by spectral and temperature dependent measurements in a two- and a three-beam four-wave mixing configuration. The observed PCP is attributed to the formation of an electron grating formed by the interference of coherent excitons that enables the storage of four different logic bits in a three-beam configuration. The different bits can be distinguished by the diffracted signal intensities and by their filed polarizations. The high efficiency of this PCP detectable at an average power level of a few $\mu $W makes it attractive for applications in all optical data processing. Also interesting for optical switch applications is the possibility to erase the PCP by a temporal overlap of the exciting pulses. All characteristic features of the effect are explained and reproduced by numerical calculations based on optical Bloch equations for a three-level system. [Preview Abstract] |
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