Atom Superposition Research Articles

Role of dephasing in modifying the evolution of the cavity radiation of a coherent beat laser

Detailed derivation of the master equation and corresponding time evolution of the cavity radiation of coherent beat laser in terms of the $c$-number variables associated with the normal ordering is presented. Although the obtained expressions in general turn out to have the same form as when dephasing is not taken into consideration, there is clear evidence that the quantum features of the cavity radiation can be significantly affected by the rate of dephasing. It is shown based on intuitive argument that the degree of two-mode squeezing and entanglement decrease with the rate of dephasing. Moreover, a thorough study of the effects of the rate at which the atomic coherent superposition is decaying is expected to aid in determining the actual available various quantum properties of the generated radiation.

Four-wave-mixing stopped light in hot atomic rubidium vapour

Digital signal processing, holography, and quantum and classical information processing rely heavily upon recording the amplitude and phase of coherent optical signals. One method for achieving coherent information storage makes use of electromagnetically induced transparency. Storage is achieved by compressing the optical pulse using the steep dispersion of the electromagnetically induced transparency medium and then mapping the electric field to local atomic quantum-state superpositions. Here we show that nonlinear optical processes may enhance pulse compression and storage, and that information about the nonlinear process itself may be stored coherently. We report on a pulse storage scheme in hot atomic rubidium vapour, in which a four-wave-mixing normal mode is stored using a double- configuration. The entire (broadened) waveform of the input signal is recovered after several hundred microseconds (1/e time of about 120 s), as well as a new optical mode (idler) generated from the four-wave-mixing process.

A note on approximate teleportation of an unknown atomic state in the two-photon Jaynes–Cummings model

We consider recent schemes [J.M. Liu, B. Weng, Physica A 367 (2006) 215] to teleport unknown atomic states and superposition of zero- and two-photon states using the two-photon Jaynes–Cummings model. Here we do the same using the “full two-photon Jaynes–Cumming”, valid for arbitrary average number of photons. The success probability and fidelity of this teleportation are also considered.

Effect of biased noise fluctuations on the output radiation of coherent beat laser

Effect of biased noise fluctuations on the degree of squeezing as well as the intensity of a radiation generated by a one-photon coherent beat laser is presented. It turns out that the radiation exhibits squeezing inside and outside the cavity under certain conditions. The degree of squeezing is enhanced by the biased noise input significantly in both regions. Despite the presence of the biased environment modes outside the cavity, the degree of squeezing outside the cavity can be greater than or equal to or even less than the cavity radiation depending on the initial preparation of the atomic superposition and amplitude of the external driving radiation. But the intensity of the radiation is found to be lesser outside the cavity regardless of these parameters.

Solvatochromism, molecular and electronic structures of trans and cis isomers of a typical styryl pyridinium cyanine dye

This paper reports on solvatochromism and molecular and electronic structures of a typical styryl pyridinium cyanine dye, 1-methyl-4-( p- N, N-dimethyl-amino styryl) pyridinium iodide (Cy) in both ground and excited states. There is a hypsochromic shift of the longest absorption band, which is greater than that of the bathochromic shift of the fluorescence band, with a decrease of the Stokes shift as the solvent polarity decreases. The results confirm the importance of decreasing the dipole moment of Cy upon excitation and solvent polarity function F( D, n), which describes the orientation polarizability of the solvent, in the energetic stabilization of Cy dye in S o and S 1 states. Semiempirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) and PM3 methods were also performed. The change of the dipole moment upon excitation was explained on the basis of changes in the charge redistribution over the whole skeleton of the molecules, which agree well with the experimental results. Also, the nature and energy of the electronic transitions were elucidated and discussed in relation to the experimental data.

1H NMR, IR and UV/VIS Spectroscopic Studies of Some Schiff Bases Derived from 2‐Aminobenzothiazole and 2‐Amino‐3‐Hydroxypyridine

AbstractBy condensing 2‐aminobenzothiazole with 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxybenzaldehyde, 4‐methoxybenzaldehyde, 4‐hydroxybenzal‐dehyde, benzaldehyde and 4‐dimethylaminobenzaldehyde, and five Schiff bases Ia‐Ie are prepared. Also, two Schiff bases IIa and IIb are prepared by condensation of 2‐amino‐3‐hydroxypyridine with 2‐hydroxy‐1‐naphthaldehyde and 2‐hydroxybenzaldehyde. The 1H NMR, IR and UV/Vis spectra of these seven Schiff bases are investigated. The signals of the 1H NMR spectra as well as the important bands in the IR spectra are considered and discussed in relation to molecular structure. The UV/Vis absorption bands in ethanol are assigned to the corresponding electronic transitions and the electronic absorption spectra of Schiff bases Ib and IIb are studied in organic solvents of different polarities. The UV/Vis absorption spectra of 2‐amino‐3‐hydroxypyridine Schiff bases IIa and IIb are investigated in buffer solutions of different pH values containing 5% (v/v) methanol, and the results are utilized for the determination of pKa and ΔG* of the ionization of the phenolic OH‐groups. The fluorescence spectra of IIa and IIb are studied in organic solvents of different polarities.The obtained spectral results are confirmed by some molecular calculations using the atom super position and electron delocalization molecular orbital theory for the Schiff base IIb.

Crystal Structure of Soluble Domain of Malaria Sporozoite Protein UIS3 in Complex with Lipid

Malaria parasite UIS3 (up-regulated in infective sporozoites gene 3) is essential for sporozoite development in infected hepatocytes. UIS3 encodes for a membrane protein that is localized to the parasite parasitophorous vacuolar membrane in infected hepatocytes. We describe here 2.5-Å resolution crystal structure of Plasmodium falciparum UIS3 soluble domain (PfUIS3130-229) in complex with the lipid phosphatidylethanolamine (PE). PfUIS3130-229 is a novel, compact, and all α-helical structure bound to one molecule of PE. The PfUIS3130-229-PE complex structure reveals a novel binding site with specific interactions between PfUIS3130-229 and the PE head group. One acyl chain of PE wraps around part of PfUIS3130-229 and docks onto a hydrophobic channel. We additionally provide new structural and biochemical evidence of PfUIS3130-229 interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein. The direct interaction of PfUIS3130-229 with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids. Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites. Given that PfUIS3 is essential for establishment of liver stage infection by P. falciparum, our data provide a new target for abrogating parasite development within liver cells before typical symptoms of malaria can manifest.

Evolution of the pair-coherent state with the two-qubit: entanglement and cat-state generation

In this paper, we study the interaction between two two-level atoms and two nondegenerate cavity modes when the atoms and the field are initially in the atomic superposition states and the pair-coherent state (PCS), respectively. We investigate the atomic inversions, tangles and joint probability distribution. We show that the system can generate long-living entanglement by controlling the values of the interaction parameters. Also we show generally that for obtaining a large amount of entanglement from two qubits interacting with a maximally entangled two-mode state one has to prepare the qubits initially in the decoupled states. Moreover, the system – at certain values of interaction parameters – can generate different types of nonclassical states, such as the mth-photon PCS, statistical mixtures of PCSs and superposition of PCS.

A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.

HYDROGEN ADSORPTION AND DIFFUSION ON A Pt(111) CLUSTER

The interaction of hydrogen with a platinum (111) cluster using the atom superposition and electron delocalization–higher binding ASED-TB quantum calculation method was studied. The metal surface was represented by a Pt cluster of seven layers. The effect of hydrogen on this metal substrate was studied by the analysis of density of states and crystal orbital overlap populations curves. The energy surface plots allow us to find a possible diffusion path through the cluster from one side to the other. The Pt – Pt metal bond is weakened during H adsorption and diffusion. The main components in the Pt – H bond are the Pt 6s (31%), 6p (26%), and 5 d xz (16%) orbitals.

COMPARATIVE STUDY OF Fe–C–H INTERACTION NEAR LINE AND POINT DEFECTS IN IRON STRUCTURES

The Fe – C – H interaction near defects in iron structures was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalization molecular orbital. Calculations were performed using three Fe clusters to simulate an edge dislocation, a divacancy; both in bcc iron and a stacking fault in an fcc iron structure. In all cases, the most stable location for C atom inside the clusters was determined. Therefore, H atom was approximated to a minimum energy region where the C atom resides. The total energy of the cluster decreases when the C atom is located near the defects zone. In addition, the presence of C in the defects zone makes no favorable H accumulation. The C acts as an expeller of H in a way that reduces the hydrogen Fe – Fe bonds weakening.

Experimental and theoretical positron annihilation studies on bulk nickel silicides

Bulk nickel silicides (NiSi and NiSi 2) have been studied using the experimental positron lifetime and depth-resolved positron beam measurements. Ab-initio calculations of positron lifetime for the silicides have also been carried out using the atomic superposition method. For NiSi phase, it is found that the theoretically computed positron lifetime compares favourably with the experimentally deduced value indicating that NiSi is defect free. However, for NiSi 2, the experimental positron lifetime does not compare well with the theoretical value suggesting that NiSi 2 contains vacancy defects. This is further supported by the positron diffusion lengths deduced from the VEPFIT analysis of the positron beam results.

Positron annihilation in vacancies at grain boundaries in metals

The behavior of vacancies in selected coherent grain boundaries (GBs) in Fe and Ni is studied by means of molecular dynamics simulations. Corresponding positron lifetimes are calculated using the atomic superposition method. There is a difference between the vacancy behavior in Fe and Ni in dependence on temperature. In Ni, vacancies at GBs appear to diminish substantially their free volume (and lifetime) with the increasing temperature, which can be attributed to ‘vacancy delocalization’. Contrary, GB vacancies remain stable up to apparently higher temperatures in Fe.

Structure of peptidyl-tRNA hydrolase 2 fromPyrococcus horikoshiiOT3: insight into the functional role of its dimeric state

Peptidyl-tRNA hydrolases catalyze the hydrolytic removal of the peptidyl moiety from the peptidyl-tRNA molecule to prevent misreading during translation. Here, the expression, purification, crystallization and X-ray diffraction study of peptidyl-tRNA hydrolase 2 from Pyrococcus horikoshii OT3 (PhPth2) are described. The crystal structures were determined as similar biological dimers in two different forms: P4(1)2(1)2 at 1.2 A resolution (form 1) and P4(3)22 at 1.9 A resolution (form 2). In the form 1 structure, the asymmetric unit contains one PhPth2 subunit and a crystallographic twofold axis defines the dimeric association with the cognate subunit. In the form 2 structure, there are two PhPth2 subunits in the asymmetric unit that make a similar dimer with a noncrystallographic twofold axis. In order to evaluate the thermodynamic stability, the intra-protomer and inter-protomer interactions of PhPth2 were analyzed and compared with those of other Pth2-family members. The thermodynamic parameters show that the large number of ion pairs compared with family members from other mesophilic organisms would contribute to the thermostability of PhPth2. The structural difference between the two dimers was quantitatively evaluated by a multiple C(alpha)-atom superposition. A significant structural difference between the two dimers was observed around the putative active site of this enzyme. A rigid-body rotation takes place so as to retain the dimeric twofold symmetry, suggesting positive cooperativity upon tRNA binding. The mechanism of ligand binding was further investigated using a docking model with a tRNA molecule. The docking study suggests that the binding of tRNA requires its simultaneous interaction with both subunits of the PhPth2 dimer.

Faithfully probabilistic teleportation of an unknown atomic state and cavity field state with a single measurement

This paper shows that, based on the single-photon JC model depicting the resonant interaction of a two-level atom with a single cavity mode, an unknown atomic state and cavity photon superposition state can be faithfully teleported with only a single measurement. The scheme is probabilistic, its success lies on the event that the sender atom (or the medi-atom, for teleportation of cavity field state) is detected in the higher state. The scheme is in contrast to the previous ones of using a maximally two-particle entangled state as quantum channel.

Entanglement in the Bimodal Jaynes–Cummings Model with the Two-Mode Squeezed Vacuum State

In this paper, we study the interaction between the two-level atom and a bimodal cavity field, namely, two-mode Jaynes–Cummings model when the atom and the modes are initially in the atomic superposition state and two-mode squeezed vacuum state, respectively. For this system we investigate the atomic inversion, linear entropy and atomic Wehrl entropy. We show that there is a connection between all these quantities. Also we prove that the atomic Wehrl entropy exhibits behaviors similar to those of the linear entropy and the von Neumann entropy. Moreover, we show that the bipartite exhibits periodical disentanglement and derive the explicit forms of the states of the atom and the modes at these values of the interaction times.

Positron annihilation in three zirconia polymorphs

AbstractPositron lifetimes and high momentum profiles both for the perfect lattice and selected defects are calculated in three (cubic, tetragonal and monoclinic) zirconia polymorphs using the atomic superposition method. Theoretical data are compared with the measured positron lifetime for cubic and tetragonal monocrystals of yttria‐stabilized zirconia (YSZ) and coincidence Doppler broadening measurements on tetragonal monocrystals of YSZ. Positron lifetime spectra of YSZ monocrystals exhibit a single component spectrum with lifetimes 178 ps and 174 ps for cubic and tetragonal phases, respectively. Possible interpretations of measured lifetime and Doppler data are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Positron annihilation at grain boundaries in metals

AbstractPositron annihilation at selected tilt and twist grain boundaries in iron and nickel is examined theoretically. First the atomic structure of studied perfect and imperfect grain boundaries is obtained using molecular dynamics simulations. Characteristics of positrons trapped at such GBs are then calculated employing the atomic superposition method and are related to free volumes found at GBs. It is observed that in some cases vacancies introduced into ideal grain boundaries do not result in an increase of the positron lifetime. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Positron annihilation in structural vacancies in Al‐rich NiAl alloys

AbstractPositron annihilation in structural vacancies in B 2 Al‐rich NiAl alloys is studied theoretically. For this purpose we use the atomic superposition method combined with molecular dynamics employed for relaxations of random vacancy configurations. We found that the defect lifetime decreases with the increasing Ni vacancy concentration. Calculated positron lifetimes are discussed in terms of the ‘vacancy‐superstructure' effect and compared with experimental positron lifetime data available. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CAALIGN: a program for pairwise and multiple protein-structure alignment

Coordinate superposition of proteins provides a structural basis to protein similarity and therefore complements the technique of sequence alignment. Methods that carry out structure alignment are faced with the problem of the large number of trials necessary to determine the optimal alignment solution. This article presents a method of carrying out rapid (subsecond) protein-structure alignment between pairs of proteins based on a maximal C(alpha)-atom superposition. The algorithm can return alignments of 12 or more residues in length as multiple non-overlapping solutions of alignment between a pair of proteins which are independent of the fold connectivity and secondary-structure content. The algorithm is equally effective for all protein fold types and can align proteins containing no secondary-structure elements such as is the case when searching for common turn structures in proteins. It has high sensitivity and returns the set of true positive results before any false positives as judged by SCOP classification. It can find alignments between topologically different folds and returns information about sequence alignment based on structure alignment. Additionally, this algorithm has been extended to carry out multiple structure alignment to determine common structures within groups of proteins, including the nondegenerate set of proteins in the PDB. The algorithm has been implemented within the program CAALIGN and this article presents results from pairwise structure alignment, multiple structure alignment and the generation of common structure fragments found within the PDB using multiple structure alignment.