Search results for "quantum mechanics."
showing 10 items of 2417 documents
Spectral long-range interaction of temporal incoherent solitons.
2014
We study the interaction of temporal incoherent solitons sustained by a highly noninstantaneous (Raman-like) nonlinear response. The incoherent solitons exhibit a nonmutual interaction, which can be either attractive or repulsive depending on their relative initial distance. The analysis reveals that incoherent solitons exhibit a long-range interaction in frequency space, which is in contrast with the expected spectral short-range interaction described by the usual approach based on the Raman-like spectral gain curve. Both phenomena of anomalous interaction and spectral long-range behavior of incoherent solitons are described in detail by a long-range Vlasov equation.
Impact of self-steepening on incoherent dispersive spectral shocks and collapse-like spectral singularities
2014
International audience; Incoherent dispersive shock waves and collapselike singularities have been recently predicted to occur in the spectral evolution of an incoherent optical wave that propagates in a noninstantaneous nonlinear medium. Here we extend this work by considering the generalized nonlinear Schrödinger equation. We show that self-steepening significantly affects these incoherent spectral singularities: (i) It leads to a delay in the development of incoherent dispersive shocks, and (ii) it arrests the incoherent collapse singularity. Furthermore, we show that the spectral collapselike behavior can be exploited to achieve a significant enhancement (by two orders of magnitudes) of…
Reliable signal processing using parallel arrays of non-identical nanostructures and stochastic resonance
2010
In the stochastic resonance (SR) phenomena, the response of a non-linear system to a weak periodic input signal is optimised by the presence of a particular level of noise which enhances signal detection. We explore, theoretically, the influence of thermal noise in arrays of metal nanoparticles functionalised with organic ligands acting as tunnelling junctions, with emphasis on the interplay between the SR phenomena and the nanostructure variability. In this system, the transference of a reduced number of electrons may suffice to implement a variety of electronic functions. However, because nanostructures are expected to show a significant variability in their physical characteristics, it i…
Strong-coupling expansions for the -symmetric oscillators
1998
We study the traditional problem of convergence of perturbation expansions when the hermiticity of the Hamiltonian is relaxed to a weaker symmetry. An elementary and quite exceptional cubic anharmonic oscillator is chosen as an illustrative example of such models. We describe its perturbative features paying particular attention to the strong-coupling regime. Efficient numerical perturbation theory proves suitable for such a purpose.
Modified Landau levels, damped harmonic oscillator and two-dimensional pseudo-bosons
2010
In a series of recent papers one of us has analyzed in some details a class of elementary excitations called {\em pseudo-bosons}. They arise from a special deformation of the canonical commutation relation $[a,a^\dagger]=\1$, which is replaced by $[a,b]=\1$, with $b$ not necessarily equal to $a^\dagger$. Here, after a two-dimensional extension of the general framework, we apply the theory to a generalized version of the two-dimensional Hamiltonian describing Landau levels. Moreover, for this system, we discuss coherent states and we deduce a resolution of the identity. We also consider a different class of examples arising from a classical system, i.e. a damped harmonic oscillator.
2MOLCAS as a development platform for quantum chemistry software
2004
This work presents the quantum chemistry package MOLCAS, with emphasis on its usefulness as a platform for developing new quantum chemical codes, and the reader is assumed to be familiar with such a process. The development of new codes for quantum chemistry is a time-consuming job that can be dramatically simplified by using libraries for standard problems (such as calculation of integrals), and tools to surmount computer language and operating system limitations. The MOLCAS quantum chemistry software contains modules for a variety of quantum chemical methods, such as Hartree-Fock (HF), density functional theory (DFT), coupled-cluster (CC), and multiconfigurational (MCSCF) approaches, incl…
Density Functional Study of Spin State in CpM(NO)X2 (M = Mo, Cr; X = Cl, NH2, CH3): Spectrochemical and Nephelauxetic Effects in Organometallic Comp…
1998
International audience; The relationship between spin state and metal−ligand bonding interactions in CpM(NO)X2 species was investigated using density functional computational techniques. The geometries of CpM(NO)Cl2 (M = Cr, Mo), CpCr(NO)(NH2)X, and CpCr(NO)(CH3)X (X = Cl, CH3) were optimized at the DFT-B3LYP level for both the diamagnetic (S = 0) and paramagnetic (S = 1) electronic configurations. While the geometric parameters of the singlet compounds matched well with structures determined experimentally, the Cr−NO bond lengths in the triplet species exceeded the experimentally observed range by a significant margin, thereby indicating a propensity for nitrosyl-ligand dissociation from t…
Noncritical quadrature squeezing through spontaneous polarization symmetry breaking
2010
We discuss the possibility of generating noncritical quadrature squeezing by spontaneous polarization symmetry breaking. We first consider Type II frequency-degenerate optical parametric oscillators but discard them for a number of reasons. Then we propose a four-wave-mixing cavity, in which the polarization of the output mode is always linear but has an arbitrary orientation. We show that in such a cavity, complete noise suppression in a quadrature of the output field occurs, irrespective of the parameter values.
Quasi diabatic CASSCF state functions
2002
A new method to determine quasi diabatic (QD) CASSCF states is presented. The adiabatic states are subjected to a unitary transformation resulting from diagonalization of a state-selection operator. The latter is constructed from the overlap of the adiabatic states with a suitable set of reference states. The multi-state (MS) CASPT2 method is used to account for the dynamical correlation effects in an approach where the QD-CASSCF wave functions are used as reference states. The procedure is applied to avoided crossings in excited states of BeH, LiO and ozone. The advantages of the proposed formulation are discussed.
Signatures of noise-enhanced stability in metastable state
2005
The lifetime of a metastable state in the transient dynamics of an overdamped Brownian particle is analyzed, both in terms of the mean first passage time and by means of the mean growth rate coefficient. Both quantities feature non monotonic behaviors as a function of the noise intensity, and are independent signatures of the noise enhanced stability effect. They can therefore be alternatively used to evaluate and estimate the presence of this phenomenon, which characterizes metastability in nonlinear physical systems.