From superradiant Rayleigh scattering to Bragg scattering

We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate interacting with far off resonant laser light. Due to superradiant Rayleigh scattering a coherent superposition of two atomic wavepackets with different momenta forms in the presence of a single laser beam. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wavepackets.     

Decoherence Control of Single- and Multi-Partite Wavepackets

A comprehensive strategy, based on controlled time-dependent perturbations, is shown to effectively protect from decoherence either bound or continuous wavepackets, characterizing single- or entangled multi-partite systems Applications to cold atoms, BEC, Josephson junctions and entangled pairs of guided photons are discussed.     

Discriminability of tryptophan containing dipeptides using quantum control

We show that the coherent manipulation of molecular wavepackets in the excited states of trp-containing dipeptides allows efficient discrimination among them. Optimal dynamic discrimination fails, however, for some dipeptide couples. When considering the limited spectral resources at play (3 nm bandwidth at 266 nm), we discuss the concept of discriminability, which appears uncorrelated to both static spectra and relaxation lifetimes.     

Preferred states of the apparatus

A simple one-dimensional model for the system–apparatus interaction is analysed. The system is a spin-1/2 particle, and its position and momentum degrees constitute the apparatus. An analysis involving only unitary Schrödinger dynamics illustrates the nature of the correlations established in the system–apparatus entangled state. It is shown that even in the absence of any environment-induced decoherence, or any other measurement model, certain initial states of the apparatus – like localized Gaussian wavepackets – are preferred over others, in terms of measurementlike one-to-one correlations in the pure system–apparatus entangled state.     

Lifetimes of the electronic-vibrational-rotational states of hydrogen molecule (Review)

Data on the lifetimes of the vibrational-rotational levels of the excited electronic states of hydrogen molecule (including H₂, D₂, HD, DT, and T₂ isotopomers) are reviewed. All data on the rotational sublevels of the lowest vibrational levels of various electronic states are presented, which were available before June 2001. A comparative analysis of the data obtained by various researchers using different methods (experimental, semi-empirical, and non-empirical) is performed for the first time. The influence of non-adiabatic intramolecular interactions on the dependence of lifetimes of the rovibronic levels of hydrogen molecule on the vibrational and rotational quantum numbers is discussed. A set of reliable data is selected which can be recommended for use in various applications.     

Experimental and theoretical evidence for long-lived molecular hydrogen anions H2- and D2-

The existence of (metastable) molecular hydrogen anions H2(-), D2(-), and H3(-) is demonstrated. These anion species were produced by sputtering of TiH2 and TiD2 targets with Cs+ ions and were identified by accelerator mass spectrometry. From the respective flight times through the spectrometer, lifetimes for H2(-) and D2(-) of at least 3 micros and 4 micros, respectively, can be inferred. Theoretical calculations within the nonlocal resonance model predict the existence of highly rotationally excited anions with lifetimes in the micros range. It is proposed that in sputtering molecular hydrogen species with high rotational and vibrational excitation are formed that are stable on the time scale of the experiment.     

Lifetime measurement in the α system (C3Δ3-X3Δ3) of TiO

The radiative lifetimes of two rotational levels of the v′ = 2 level of the C³Δ₃ state of TiO have been measured using laser-induced fluorescence and delayed coincidence counting. Individual rotational levels are excited and observed. The measured lifetimes are τ_{J = 17} = 28.21 + 0.15 nsec and τ_{J = 87} = 29.74 ± 0.86 nsec. Argon-TiO collision cross sections have been determined for the two rotational levels and are found to differ by 30%.     

Electron spin decoherence in isotope-enriched silicon

Silicon is promising for spin-based quantum computation because nuclear spins, a source of magnetic noise, may be eliminated through isotopic enrichment. Long spin decoherence times T2 have been measured in isotope-enriched silicon but come far short of the T2=2T1 limit. The effect of nuclear spins on T2 is well established. However, the effect of background electron spins from ever present residual phosphorus impurities in silicon can also produce significant decoherence. We study spin decoherence decay as a function of donor concentration, 29Si concentration, and temperature using cluster expansion techniques specifically adapted to the problem of a sparse dipolarly coupled electron spin bath. Our results agree with the existing experimental spin echo data in Si:P and establish the importance of background dopants as the ultimate decoherence mechanism in isotope-enriched silicon.     

低振动激发HeI2分子振动预离解寿命和终转动态分布

用含时黄金规则波包法，对ＨｅＩ２分子在低初始振动激发（ｖ＜１２）态下振动预离解动力学作了全维量子力学计算。所预言的总衰变宽度和寿命与谱线宽和皮秒时间分解的实时态－态测量外推数据符合得相当好。计算的总衰变宽度对初始振动态ｖ是敏感的并呈现一种非线性关系。结果表明低振动激发ＨｅＩ２分子衰变模式仍应是量子力学的。除终态相互作用对决定终转动分布有重要作用以外，首次发现，低振动激发态的初始特性也能显著影响终转动态分布。用Ｉ２的转动常数对ｖ的关系合理地解释了这个独特现象     

超冷铯分子纯长程态转动常数的精密测量

利用调制的俘获损耗光谱技术实验测量了超冷铯分子纯长程0_g^-态的高分辨光谱. 采用双光缔合光谱技术构建了精确的频率差参考信号, 对转动能级的共振频率间隔进行了精确的标定, 获得了转动能级频率间隔与转动量子数的关系. 通过将实验数据拟合到非刚性转动模型, 获得了超冷铯分子纯长程0_g^-态不同振动态的转动常数. 实验结果表明转动常数随振动量子数的增加而线性减小, 线性递减率为-0.41 MHz±0.01 MHz. 关键词： 双光缔合光谱技术 超冷铯分子 转动常数 纯长程态     

Lifetime Measurements of the DΠ State of HfS and the bΠ1 State of HfO

Lifetime measurements of individual rotational levels in excited states of hafnium oxide and hafnium sulfide have been performed using population probing by resonant two-photon ionization in a molecular beam. For the b³Π₁ state of HfO rotational levels in the vibrational level v=0 were found to have lifetimes in the region 650-700 ns. For the D¹Π state of HfS rotational level lifetimes in the vibrational levels v=0 and v=1 were determined to be around 240 ns. The technique used here provides very accurate results and the uncertainty in the reported values is only about 2%. Possible sources of errors are examined. The absorption oscillator strengths from the ground state are calculated.     

Decoupling Bang-Bang Group for Adiabatic Decoherence Control in a Three-Level Atom

In this paper, we study the control problem of adiabatic decoherence in a three-level atom. We will find the decoupling bang-bang group for various configurations, including the V configuration and the cascade type of three-levelatom subjected to adiabatic decoherence. We also give the programs to design a sequence of periodic twinborn pulses to suppress the decoherence.     

Lifetimes of rovibrational levels of the long-range I′ 1Πg state of H2 and D2: experiment and theory

The lifetimes of the lowest lying rovibrational levels of the outer well I′ ¹Π_g state of molecular hydrogen were measured for both H₂ and D₂. The measurements were made by direct observation of the time-dependent decay of the fluorescence. The observed lifetimes depend on isotopomer and increase with vibrational excitation. The predominant decay route for these levels is fluorescence. Previously published ab initio lifetimes calculated for these states, which accounted for non-adiabatic interactions [J. Chem. Phys. 92, 7461 (1990)], are in good agreement with experiment for H₂ but are too long by four or five orders of magnitude for D₂. We present new ab initio results at the adiabatic level for the fluorescence lifetimes. The current results are in reasonable agreement with the experimental lifetimes for both H₂ and D₂. We explain the isotopomer and vibrational dependence of the lifetimes and discuss the neglected interactions and decay pathways.     

Pressure Effect on Solvation Dynamics and Rotational Dynamics in Solution

Effects of pressure on solvation dynamics and rotational dynamics in solution were studied by picosecond time-dependent fluorescence Stokes shift (TDFSS) and picosecond time-dependent fluorescence rotational depolarization (TDFRD). The fluorescence lifetimes of solute probes, coumarin 153 and p -terphenyl, in various solvents were measured at high pressures by time-correlated single photon counting (TCSPC) technique with time resolution of 20-30 ps.     

Decoupling Bang-Bang Group for Adiabatic Decoherence Control in a Three-Level Atom

In this paper, we study the control problem of adiabatic decoherence in a three-level atom. We will find thedecoupling bang-bang group for various configurations, including the V configuration and the cascade type of three-level atom subjected to adiabatic decoherence. We also give the programs to design a sequence of periodic twinborn pulses to suppress the decoherence.     

Information content of high harmonics generated from aligned molecules

We derive an expression for the harmonic signal from nonadiabatically aligned molecules that accounts for both electronic and rotational motions. We identify a single approximation, which converts the expression into a physically transparent and computationally convenient form. Our analytical result gives explicitly the time dependence of the harmonic spectra, thus explaining the observations of a class of recent experiments. Moreover, it points to new opportunities for generating insights into the structure and dynamics of molecular systems through harmonic generation experiments from aligned molecules. This includes information regarding the rotational and electronic dynamics of isolated systems, as well as regarding the decoherence and relaxation in molecules subject to a dissipative environment.     

General Decoherence Suppression in Three-Level Atom in V- and Ξ-Configurations

In this paper, we present the decoupling bang-bang （BB） twin-born pulses to suppress the genera/deco- herence, both amplitude and phase decoherence, in a three-level atom in V- and Ξ-configurations. We give the exact sequence of periodic twinborn pulses in such systems.     

Fullerene quantum gyroscope

We report the observation of quantized rotational states of a diatomic C2 unit in solid endohedral fullerene C(2)Sc(2)@C(84). The rotational transitions induce a periodic line pattern in the low energy Raman spectrum. The rotational constant B and the C-C distance were found to be 1.73 cm(-1) and 0.127 nm, respectively. Density functional calculations revealed an intrinsic rotational barrier of the order of only a few meV for the C2 unit. The Schr?dinger equation involving the potential barrier was solved and the Raman tensor matrix elements were calculated, yielding good quantitative agreement with the experiment. To our best knowledge this is the first intrinsic rotational spectrum of a diatomic plane molecular rotor.     

Entangled and disentangled decoherence of intermediate electron-hole pairs in two-photon photoemission from surface bands: beyond the adiabatic approximation

We discuss the effects which combinations of entangled and disentangled decoherence and transient response induce on the early decay of coherent electron-hole pairs in the intermediate states of two-photon photoemission (2PPE) from image potential bands. We find that their interplay gives rise to deviations of the pair decay probabilities from simple exponential laws governed by independent quasiparticle lifetimes obtained in the self-energes based on the adiabatic hypothesis. Assessment of these effects for paradigmatic Cu(111) surface shows that they are most pronounced in the interval of pump-probe photon pulse delay times typical of current 2PPE experiments.