Narrow Results

The interaction of a two-level XYn-spin system with a two-mode cavity field is investigated through a generalized Jaynes-Cummings model in the rotating wave approximation. The spontaneous decay of a spin level was treated by considering the interaction of the two-level spin system with the modes of the universe in the vacuum state. The different cases of interest, characterized in terms of a detuning parameter for each mode, which emerge from the nonvanishing of certain commutation relations between interaction picture Hamiltonians associated with each mode, were analytically implemented and numerically discussed for various values of the initial mean photon number and spin-photon coupling constants. Photon distribution, time evolution of the spin population inversion, as well as the statistical properties of the field leading to the possible production of nonclassical states, such as antibunched light and violations of the Cauchy-Schwartz inequality are examined for an excited initial state. It was assumed that the two modes are initially in coherent states and have the same photon distribution. The case of zero detuning of both modes was treated in terms of a linearization of the expansion of the time evolution operator, while in other three cases, the computations were conducted via second- and third-order Dyson perturbation expansion of the time evolution operator matrix elements for the excited and ground states respectively.

Normal squeezing, variance and entropy squeezing factors based on the Heisenberg uncertainty principle and Shannon information entropy theory, respectively, derived from the entangled states of two-mode coherent states in two-photon processes are numerically investigated through a previously developed generalized nonlinear Jaynes–Cummings two-level spin model. Numerical simulations are performed and discussed for two two-photon model Hamiltonians in both resonant and off-resonant states of the spin system with the bimodal cavity field.

We present a general formalism for the dissipative dynamics of an arbitrary quantum system in the presence of a classical stochastic process. It is applicable to a wide range of physical situations, and in particular it can be used for qubit arrays in the presence of classical two-level systems (TLS). In this formalism, all decoherence rates appear as eigenvalues of an evolution matrix. Thus the method is linear, and the close analogy to Hamiltonian systems opens up a toolbox of well-developed methods such as perturbation theory and mean-field theory. We apply the method to the problem of a single qubit in the presence of TLS that give rise to pure dephasing 1/f noise and solve this problem exactly.

We consider a non-Hermitian Hamiltonian in order to effectively describe a two-level system (TLS) coupled to a generic dissipative environment. The total Hamiltonian of the model is obtained by adding a general anti-Hermitian part, depending on four parameters, to the Hermitian Hamiltonian of a tunneling TLS. The time evolution is formulated and derived in terms of the normalized density operator of the model, different types of decays are revealed and analyzed. In particular, the population difference and coherence are defined and calculated analytically. We have been able to mimic various physical situations with different properties, such as dephasing, vanishing population difference and purification.

The elementary jumps in the electron current through conducting filaments of two nanometer-sized virtual memristor structures consisting of a contact of a conductive atomic force microscope probe to the Si₃N₄ layer with the thickness of 6nm deposited onto the $n^{++}$-Si(001) conductive substrates are investigated. These structures are: (S1) the Si₃N₄/Si film; (S2) the Si₃N₄/SiO₂/Si stack, a similar structure with 2nm SiO₂ sublayer between the film and the substrate. Usually, such investigations are performed by the analysis of the waveform of this current with the aim of extracting the random telegraph noise (RTN). Here, we develop a new indirect method, which is based on the measurement of the spectrum of the low-frequency flicker noise in the current without extracting the RTN. We propose that the flicker noise is caused by the motion (drift/diffusion) of nitrogen ions via vacancies within and around the filament. The number of these ions is estimated by taking into account the geometrical parameters of the filament. This allows us to estimate the root mean square magnitude $i_0$ of the current jumps, which are caused by random jumps of nitrogen ions, and the number M of these ions. This is fundamental for understanding the elementary mechanisms of the electron current flowing through the filament and the resistive switching in memristor devices.

In terms of a new Hamiltonian we introduce a modified Jaynes–Cummings model to represent the interaction between a two-level atom and two electromagnetic fields injected simultaneously within a perfect cavity. The field–field interaction is assumed to be in the frequency converter form. Exact expressions of the dynamical operators is given by solving the equations of the motion in the Heisenberg picture. The entropy squeezing is examined in the framework of Shannon information entropy. Using the entropic uncertainty relation, one can be able to show that there is a new kind of quantum squeezing in the entropy.