Results 1 - 10 of 943
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[en] We demonstrate a simple way to realize control of population transfer and creation of two orthogonal maximally superposition states in a Λ-type four-level system with closely spaced doublet target states via a pair of pump and chirped Stokes pulses. It is illustrated that the population in the initial state can be selectively, completely and robustly transferred to either of the doublet target states via chirped adiabatic passage with the suitable chirp rate and frequency detuning of the Stokes pulse. Besides, creation of two orthogonal maximally superposition states between the initial state and intermediate state with equal amplitude but inverse relative phases is also shown, which may have potential applications in the preparations of quantum bits. (letter)
[en] Our previous paper, part I of the same study, shows the different experimental spectra used to draw a conclusion on the genuine existence of narrow, weakly excited mesonic structures having masses below and a little above the pion (M = 139.56 MeV) mass. This study  was instigated by the observation, in the Σ+ disintegration—Σ+ → pP0, P0 → μ-μ+ —of a narrow range of dimuon masses. The authors make a conclusion on the existence of a neutral intermediate state P0 with a mass M = (214.3 ± 0.5) MeV. We present here some attempts to understand the possible nature of the structures observed in part I.
[en] We study the phase-dependent propagation of a strong, resonant pump and two weak symmetrically detuned fields in a two-level system with population decay through a cascade of intermediate levels. As this system forms a closed loop, the propagation is phase-dependent. For an initial total phase Φ=0, there is constructive interference between the two weak fields, leading to parametric amplification on propagation. When Φ=π, destructive interference occurs, leading to absorption of the weak fields on propagation. When the weak fields are initially equal in intensity, and Φ=0,π, Φ remains constant on propagation. For other initial phases, Φ changes on propagation. Dramatic phase changes from π to 0 can occur when the weak fields are initially unequal in intensity and Φ=π.
[en] The dynamical behaviour of crystalline macromolecules and their surrounding solvent as a function of cryo-temperature is reviewed. X-ray crystallography provides structural details of biological macromolecules. Whereas routine data are collected close to 100 K in order to mitigate radiation damage, more exotic temperature-controlled experiments in a broader temperature range from 15 K to room temperature can provide both dynamical and structural insights. Here, the dynamical behaviour of crystalline macromolecules and their surrounding solvent as a function of cryo-temperature is reviewed. Experimental strategies of kinetic crystallography are discussed that have allowed the generation and trapping of macromolecular intermediate states by combining reaction initiation in the crystalline state with appropriate temperature profiles. A particular focus is on recruiting X-ray-induced changes for reaction initiation, thus unveiling useful aspects of radiation damage, which otherwise has to be minimized in macromolecular crystallography
[en] We present a highly efficient scheme for perfect joint remote preparation of an arbitrary -qubit W state with minimum quantum resource. Both the senders Alice and Bob intend to jointly prepare one -qubit W state for the remote receiver Charlie. In the beginning, they help the remote receiver Charlie to construct one n-qubit intermediate state which is closely related to the target -qubit W state. Afterward, Charlie introduces auxiliary qubits and applies appropriate operations to obtain the target -qubit W state. Compared with previous schemes, our scheme requires minimum quantum resource and least amount of classical communication. Moreover, our scheme has a significant potential for being adapted to remote state preparation of other special states.
[en] This paper addresses the problem of two-photon double ionization (TPDI) of He(1s2) and He(1s2s1S). First, we reconsider TPDI of He(1s2) with a photon energy of 2.1 a.u.; it is well known that TPDI is mainly a sequential process, resulting in an electron spectrum dominated by two peaks. In the past, we have noticed that the peaks are shifted as the pulse duration shortens; they move toward each other. The first objective of the present work is to clarify the origin of the shift and to evaluate it quantitatively. In parallel with the resolution of the time-dependent Schroedinger equation (TDSE), we have developed a model calculation based on lowest-order perturbation theory for the laser-atom interaction and for the atomic structure representation. The model agrees with TDSE calculations, and it also explains the physical origin of the shifts. Furthermore, it provides a quantitative evaluation of these shifts. The second objective of the present work is to extend our study to TPDI of He(1s2s1S), which has received much less attention until now. We have investigated the cases of photon energies of 1.8 and 2.5 a.u. We show that TPDI is dominated by a sequential process where the first ionization leaves a remaining He+(2s) ion, which is ionized by a second photon. As in the case of He(1s2), the model agrees with TDSE calculations, and it leads to better insights into the physics underlying the double-ionization process. (authors)
[en] The domain formation induced by perpendicular spin injection has been studied with the magnetic nanopillar structure. When the bottom layer is an unpatterned thin film, an intermediate state is observed and characterized to be a domain formed in the bottom layer. Domain formation is also investigated when the size of the top nanomagnet is increased
[en] We analyzed the process of B → φφ decay in quantum chromodynamics factorization (QCDF) and final state interaction (FSI). In QCDF for this decay we have only the annihilation graph and we expected small branching ratio. Then we considered FSI effect as a sizable correction where the intermediate states are K0K/overbar0, K+ K-, and Ds+Ds- mesons. To consider the amplitudes of these intermediate states, the QCDF approach was used. The experimental branching ratio of B → φφ is less than 2 x 10-7 and our results are 0.04 x 10-7 and 1.54 x 10-7 from QCDF and FSI, respectively. (author)
[en] In the traditional random-conformational-search model, various hypotheses with a series of meta-stable intermediate states were proposed to resolve the Levinthal paradox in protein-folding time. Here we introduce a quantum strategy to formulate protein folding as a quantum walk on a definite graph, which provides us a general framework without making hypotheses. Evaluating it by the mean of first passage time, we find that the folding time via our quantum approach is much shorter than the one obtained via classical random walks. This idea is expected to evoke more insights for future studies. (express letter)
[en] Recently, experiments on mRNA abundance (gene expression) have revealed that gene expression shows a stationary organization described by a scale-free distribution. Here we propose a constructive approach to gene expression dynamics which restores the scale-free exponent and describes the intermediate state dynamics. This approach requires only one assumption: Markov property