Publications

Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    AVERBUKH V, MOISEYEV N, MIRBACH B, KORSCH HJet al., 1995,

    DYNAMICAL TUNNELING THROUGH A CHAOTIC REGION - A CONTINUOUSLY DRIVEN RIGID ROTOR

    , ZEITSCHRIFT FUR PHYSIK D-ATOMS MOLECULES AND CLUSTERS, Vol: 35, Pages: 247-256, ISSN: 0178-7683
  • Journal article
    VITANOV NV, KNIGHT PL, 1995,

    CONTROL OF ATOMIC TRANSITIONS BY THE SYMMETRY OF EXCITATION PULSES

    , OPTICS COMMUNICATIONS, Vol: 121, Pages: 31-35, ISSN: 0030-4018
  • Journal article
    WATSON JB, KEITEL CH, KNIGHT PL, BURNETT Ket al., 1995,

    Quantum signatures in the stabilization dynamics

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 52, Pages: 4023-4028, ISSN: 1050-2947

    We investigate the phase-space dynamics of a hydrogenic atom in a very intense, high-frequency laser field, by comparing the time-dependent quantum Wigner functions with the corresponding classical distributions calculated using the Monte Carlo method. In both cases we model the atom by a one-dimensional soft-core potential in order to simplify the calculation. We demonstrate the importance of nonclassical interferences in the Wigner function and show how negative parts of it observed at the peak of the pulse are associated with the formation of a coherent superposition of dressed ‘‘Kramers-Henneberger’’ (KH) eigenstates. These signatures of the quantum dynamics are eliminated towards the end of the pulse when the coherence between the KH eigenstates degrades so that the classical and the quantum mechanical phase-space distributions come into agreement.
  • Journal article
    Knight PL, 1995,

    Rudolf Peierls (1907-1995) - Obituary

    , CONTEMPORARY PHYSICS, Vol: 36, Pages: 375-375, ISSN: 0010-7514
  • Journal article
    PROTOPAPAS M, KNIGHT PL, 1995,

    PHASE-CONTROL IN 2-COLOR MULTIPHOTON IONIZATION

    , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 28, Pages: 4459-4479, ISSN: 0953-4075
  • Journal article
    VIVIRITO RMA, KNIGHT PL, 1995,

    ADIABATIC EXCITATION AND STABILIZATION IN SHORT-RANGE POTENTIALS

    , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 28, Pages: 4357-4375, ISSN: 0953-4075
  • Journal article
    PROTOPAPAS M, SANPERA A, KNIGHT PL, BURNETT Ket al., 1995,

    High-intensity two-color interactions in the tunneling and stabilization regimes

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 52, Pages: R2527-R2530, ISSN: 1050-2947

    Two-color excitation of a hydrogen atom has been studied by solving the time-dependent Schrödinger equation. We have chosen the two laser frequencies to be the fundamental and its third harmonic with an adjustable phase between the two laser fields. This has been proposed and successfully implemented in the past for "coherent control" of atomic and chemical processes. Here we have extended the study to the high-intensity domain and well into the tunneling and the stabilization regimes. We show that in the tunneling regime the two-color excitation can enhance the intensity of harmonics by more than two orders of magnitude compared to a single color at the same effective intensity. In the stabilization regime we confirm that two-color excitation can be used to generate higher harmonics.
  • Journal article
    Hinds EA, Berkelend DJ, Boshier MG, 1995,

    Precise Optical Measurement of Lamb Shifts in Atomic Hydrogen

    , Physical Review Letters, ISSN: 0031-9007
  • Journal article
    NEW GHC, WILSON DC, 1995,

    SIMULATIONS OF RAMAN CONVERSION IN LARGE-APERTURE AMPLIFIERS

    , OPTICS COMMUNICATIONS, Vol: 119, Pages: 673-681, ISSN: 0030-4018
  • Journal article
    VITANOV NV, KNIGHT PL, 1995,

    Coherent excitation of a two-state system by a train of short pulses

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 52, Pages: 2245-2261, ISSN: 1050-2947

    A theoretical nonperturbative study of the coherent excitation of a two-state system by N consecutive equally spaced identical pulses is presented. General relations between the evolution matrix elements in the cases of one and N pulses are obtained in a closed form. For pulse envelopes allowing analytical solutions, these relations enable analytical treatment of pulse-train excitation; for pulses that can only be treated numerically, they shorten the computations by a factor of N. The relations show that the multiple-pulse excitation of a two-state system can be considered as a quantum analog of the diffraction grating. The interaction dynamics substantially depends on the way the train is produced because the phase shift that is accumulated by the probability amplitudes due to the free evolution of the system during and between the pulses differs. In the limit of weak excitation, the results recover earlier conclusions based on perturbative treatments. Simple formulas are derived for the conditions for complete population inversion (CPI) and complete population return (CPR), which differ from the single-pulse ones. These general results are applied to four particular cases that allow analytical solutions: resonant, rectangular, Rosen-Zener, and Allen-Eberly pulses. A common feature in all these cases is that the number and the amplitude of oscillations in the state populations increase with the number of pulses, while their width decreases. For rectangular pulses, CPI is possible below a given value of the ratio between the detuning and the pulse area; this value increases nearly linearly with the number of pulses.For the Rosen-Zener model, CPI is found to be possible for two and more pulses, while it is impossible for a single non-resonant pulse. It is shown that for a given number of pulses there is an upper limit on the detuning for which CPI can be observed; this limit increases logarithmically with the number of pulses. For the Allen-Eberly model, CPR is esta
  • Journal article
    GUERRA ES, DUTRA SM, KNIGHT PL, ZAGURY Net al., 1995,

    Influence of spontaneous emission on trapping states and start-up times of degenerate two-photon micromasers

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 52, Pages: 1651-1664, ISSN: 1050-2947

    We study degenerate two-photon micromasers pumped by cascade three-level atoms, where each atomic energy level has a different linewidth. Our model allows us to recover the ordinary two-photon micromaser situation when these widths vanish. In the limit of large linewidths we obtain a two-photon laser model. We show that trapping states are extremely sensitive to atomic decay, even when the decay time is small in comparison to the transit time through the cavity. Unlike the one-photon micromaser, they are sensitive to the linewidth of the upper, as well as the lower energy level. We have also studied the effects of atomic decay on the starting time of micromasers and on the noise. We found that there is a significant difference between the behavior of two-photon micromasers and lasers as we change the ratio of the widths of the upper and lower levels.
  • Journal article
    GILES AJ, POSTHUMUS JH, THOMPSON MR, FRASINSKI LJ, CODLING K, LANGLEY AJ, SHAIKH W, TADAY PFet al., 1995,

    INTERFEROMETRIC SHAPING OF FEMTOSECOND LASER-PULSES

    , OPTICS COMMUNICATIONS, Vol: 118, Pages: 537-541, ISSN: 0030-4018
  • Journal article
    KEITEL CH, KNIGHT PL, NARDUCCI LM, SCULLY MOet al., 1995,

    RESONANCE FLUORESCENCE IN A TAILORED VACUUM

    , OPTICS COMMUNICATIONS, Vol: 118, Pages: 143-153, ISSN: 0030-4018
  • Journal article
    GAUTHEY FI, KEITEL CH, KNIGHT PL, MAQUET Aet al., 1995,

    Role of initial coherence in the generation of harmonics and sidebands from a strongly driven two-level atom

    , PHYSICAL REVIEW A, Vol: 52, Pages: 525-540, ISSN: 1050-2947

    We investigate the coherent and incoherent contributions of the scattering spectrum of strongly driven two-level atoms as a function of the initial preparation of the atomic system. The initial ‘‘phasing’’ of the coherent superposition of the excited and ground states is shown to influence strongly the generation of both harmonics and hyper-Raman lines. In particular, we point out conditions under which harmonic generation can be inhibited at the expense of the hyper-Raman lines. Our numerical findings are supported by approximate analytical evaluation in the dressed state picture.
  • Journal article
    GARRAWAY BM, KIM MS, KNIGHT PL, 1995,

    QUANTUM JUMPS, ATOMIC SHELVING AND MONTE-CARLO FLUORESCENCE-SPECTRA

    , OPTICS COMMUNICATIONS, Vol: 117, Pages: 560-569, ISSN: 0030-4018
  • Journal article
    NAGAMINE K, MIYAKE Y, SHIMOMURA K, BIRRER P, MARANGOS JP, IWASAKI M, STRASSER P, KUGA Tet al., 1995,

    ULTRASLOW POSITIVE-MUON GENERATION BY LASER IONIZATION OF THERMAL MUONIUM FROM HOT TUNGSTEN AT PRIMARY PROTON-BEAM

    , PHYSICAL REVIEW LETTERS, Vol: 74, Pages: 4811-4814, ISSN: 0031-9007
  • Journal article
    DUTRA SM, KNIGHT PL, 1995,

    ON THE GENERATION OF BESSEL BEAMS BY SPONTANEOUS EMISSION IN A PLANAR MICRO-CAVITY

    , OPTICS COMMUNICATIONS, Vol: 117, Pages: 256-261, ISSN: 0030-4018
  • Journal article
    POSTHUMUS JH, FRASINSKI LJ, GILES AJ, CODLING Ket al., 1995,

    DISSOCIATIVE IONIZATION OF MOLECULES IN INTENSE LASER FIELDS - A METHOD OF PREDICTING ION KINETIC ENERGIES AND APPEARANCE INTENSITIES

    , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 28, Pages: L349-L353, ISSN: 0953-4075
  • Journal article
    VITANOV NV, KNIGHT PL, 1995,

    COHERENT EXCITATION BY ASYMMETRIC PULSES

    , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 28, Pages: 1905-1920, ISSN: 0953-4075
  • Journal article
    FICEK Z, DALTON BJ, KNIGHT PL, 1995,

    Fluorescence intensity and squeezing in a driven three-level atom: Ladder case.

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 51, Pages: 4062-4077, ISSN: 1050-2947

    A theoretical study is made of the steady-state intensity and squeezing properties of the fluorescent light from a three-level-atom system in a ladder configuration, which is subject to spontaneous-emission decay to the electromagnetic-field vacuum. Two cases are examined: in the equispaced (ES) level case, the two atomic transition frequencies are nearly equal and two photon absorption processes occur from a single coherent laser field that couples both transitions and has a small detuning from each; in the non- equispaced (NES) level case, the atomic transition frequencies are rather different and two photon absorption processes occur from two coherent laser fields, each coupled to a single transition and in near resonance with it. In both cases, a situation of small two-photon detuning occurs. Optical Bloch equations for the atomic density matrix in rotating frames are given and matrix expressions for determining the steady-state populations and coherences are obtained. Analytic expressions are also given for special cases. The fluorescent intensity is obtained from the populations of the intermediate and upper states, with the normally ordered variance (NOV) for quadrature components of the fluorescent field involving, in addition, the atomic coherences. The fluorescent intensities are shown graphically as a function of two-photon detuning for a variety of one-photon detunings and Rabi frequencies for the ES and NES cases.In both cases, the fluorescent intensities show the well known resonances from the upper state at zero two-photon detuning and from the intermediate state at zero one-photon detuning for the lower transition. However, further resonances are also found. The intermediate-state intensity displays a resonance at zero two-photon detuning. Also, the upper-state intensity shows a resonance at zero one-photon detuning for the upper transition, but only for the NES case; evidently, the transfer rate from upper to lower transition coherences destroys thi
  • Journal article
    AVERBUKH V, MOISEYEV N, 1995,

    CUTOFF IN MOLECULAR HARMONIC-GENERATION SPECTRA RESULTING FROM CLASSICAL CHAOTIC DYNAMICS

    , PHYSICAL REVIEW A, Vol: 51, Pages: 3911-3915, ISSN: 1050-2947
  • Journal article
    SZYMANOWSKI C, KEITEL CH, DALTON BJ, KNIGHT PLet al., 1995,

    SWITCHING BETWEEN RAYLEIGH-LIKE AND LORENTZIAN LINESHAPES OF THE DISPERSION IN DRIVEN 2-LEVEL ATOMS

    , JOURNAL OF MODERN OPTICS, Vol: 42, Pages: 985-1003, ISSN: 0950-0340
  • Journal article
    EKERT A, KNIGHT PL, 1995,

    ENTANGLED QUANTUM-SYSTEMS AND THE SCHMIDT DECOMPOSITION

    , AMERICAN JOURNAL OF PHYSICS, Vol: 63, Pages: 415-423, ISSN: 0002-9505
  • Journal article
    STEINBACH J, GARRAWAY BM, KNIGHT PL, 1995,

    High-order unraveling of master equations for dissipative evolution

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 51, Pages: 3302-3308, ISSN: 1050-2947

    We show how the quantum trajectory method for describing the dissipative evolution of conditioned states can be implemented in a numerically efficient higher-order unraveling that goes beyond the Euler method usually employed in such simulations. We demonstrate its applicability through an analysis of spontaneous emission and find that improvements by two orders of magnitude are possible for the specific example addressed.
  • Journal article
    NEW GHC, 1995,

    THE ORIGIN OF EXCESS NOISE

    , JOURNAL OF MODERN OPTICS, Vol: 42, Pages: 799-810, ISSN: 0950-0340
  • Journal article
    DHOLAKIA K, HORVATH GZK, POWER W, SEGAL DM, THOMPSON RCet al., 1995,

    INVESTIGATION OF ION DYNAMICS IN A PENNING TRAP USING A PULSE-PROBE TECHNIQUE

    , APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 60, Pages: 375-382, ISSN: 0946-2171
  • Journal article
    Hinds EA, Sangster K, Barnett SM, Riis E, Sinclair AGet al., 1995,

    Aharonov-Casher phase in an atomic system

    , Physical Review A, ISSN: 1050-2947
  • Journal article
    BUZEK V, KEITEL CH, KNIGHT PL, 1995,

    Sampling entropies and operational phase-space measurement. I. General formalism

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 51, Pages: 2575-2593, ISSN: 1050-2947

    We present an entropic description of quantum-mechanical states based on an operational approach to a phase-space measurement. We give a simple phase-space interpretation of sampling entropies in terms of which we derive very general entropic uncertainty relations reflecting the degree of the phase-space uncertainty of the quantum-mechanical state in the given measurement (i.e., for a given ‘‘quantum-ruler’’ state). We relate the sampling entropy to the von Neumann and Shannon entropy and show that the Wehrl entropy represents a particular example of a sampling entropy when the quantum ruler is represented by coherent states.
  • Journal article
    BUZEK V, KEITEL CH, KNIGHT PL, 1995,

    Sampling entropies and operational phase-space measurement. II. Detection of quantum coherences

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 51, Pages: 2594-2601, ISSN: 1050-2947

    We use the operational phase-space distributions and sampling entropies developed in the preceding paper [V. Bužek, C. H. Keitel, and P. L. Knight, Phys. Rev. A 51, 2575 (1995)] to discuss the nature of quantum interference between components of superpositions of states. We show how the Wehrl entropy, a special case of the sampling entropy, is a useful discriminator between different kinds of superpositions and of statistical mixtures, and is determined essentially by the coherent-state content. Apart from interference terms, this content is given by the quantum uncertainty of a single coherent state and the classical contribution to the number of coherent states necessary to tile the dominant phase-space ‘‘patch’’ representing the quantum state of interest. We illustrate these ideas using nonclassical superpositions of coherent states, where interference modifies the phase-space distributions, and show how these features are sensitive to dissipation.
  • Journal article
    Hinds EA, Sauer BE, Wang J, 1995,

    Anomalous Spin-Rotation Coupling in the X^2Σ+ State of YbF

    , Physical Review Letters, ISSN: 0031-9007

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://www.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=213&limit=30&resgrpMemberPubs=true&resgrpMemberPubs=true&page=73&respub-action=search.html Current Millis: 1725821987040 Current Time: Sun Sep 08 19:59:47 BST 2024