W. Leoński

Squeezed vacuum reservoir effect for entanglement decay in the nonlinear quantum scissor system

We discuss the coupler system of two nonlinear oscillators excited by an external coherent field prepared in a maximally entangled state (Bell-like state). We show that as a result of the coupler interaction of the system with external broadband squeezed vacuum bath, entanglement decay dynamics can be considerably affected. Besides the phenomena of sudden entanglement death and its rebirth, a shortening (or lengthening) of the total disentanglement time ?D can be observed, depending on the squeezing parameters. Moreover, in the example of one of the reborn entanglement cases it is shown that by changing the values of these parameters the maximal values of the negativity for the 3?2 system discussed can be tailored.

Generalized Bell states generation in a parametrically excited nonlinear coupler

A nonlinear Kerr-like coupler with parametric interaction is considered. It is shown that such a system can be treated as nonlinear quantum scissors enabling the generation of generalized Bell states. Moreover, the influence of the external reservoir on entanglement formation and its survival is considered.

Quantum correlations and entanglement in a model comprised of a short chain of nonlinear oscillators

We discuss a model comprised of a chain of three Kerr-like nonlinear oscillators pumped by two modes of external coherent field. We show that the system can be treated as nonlinear quantum scissors and behave as a three-qubit model. For such situation, different types of tripartite entangled states can be generated, even when damping effects are present in the system. Some amount of such entanglement can survive even in a long-time limit. The flow of bipartite entanglement between subsystems of the model and relations among first-order correlations, second-order correlations, and the entanglement are discussed.

Ground-state entanglement of spin-1 bosons undergoing superexchange interactions in optical superlattices

We will discuss a model with ultracold atoms confined in optical superlattices. In particular, we will study the ground-state properties of two spin-1 bosons trapped in a double-well potential. Depending on the external magnetic field and biquadratic interactions, different phases of magnetic order are realized. Applying von Neumann entropy and the number of relevant orbitals, we will quantify the bipartite entanglement between particles. Changing the values of the parameters determining the superlattices, we can switch the system between differently entangled states.

Photoionization electron spectra in a system interacting with a neighboring atom

Photoelectron ionization spectra of a system interacting with a neighbor two-level atom are investigated using the Laplace-transform method. These spectra are typically composed of several peaks. Photoelectron ionization spectra conditioned by the measurement on the two-level atom show oscillations at the Rabi frequency. The presence of spectral zeros occurring periodically with the Rabi period is predicted. This phenomenon is analyzed in detail.

Fano zeros in photoelectron spectra of an autoionization system interacting with a neighboring atom.

Photoelectron ionization spectra of an autoionization system interacting with a neighboring two-level atom are studied using the method of canonical transformation. Conditions for the occurrence of a Fano zero are exactly derived, together with its frequency. Ionization spectra are typically composed of at most four peaks in this case. Sharp peaks occur not far from the Fano zero due to the confluence of bound-free coherences. Spectral peaks close to the Fano zero are suppressed. Also dynamical zeros appearing once per the Rabi period in conditioned photoelectron ionization spectra are observed.

Photoelectron spectra in an autoionization system interacting with a neighboring atom

Photoelectron ionization spectra of an autoionization system with one discrete level interacting with a neighbor two-level atom are discussed. The formula for long-time ionization spectra is derived. According to this formula, the spectra can be composed of up to eight peaks. Moreover, the Fano-like zeros for weak optical pumping are identified in these spectra. The conditional ionization spectra depending on the state of the neighbor atom exhibit oscillations at the Rabi frequency. Dynamical spectral zeros occurring once per the Rabi period are revealed in these spectra.

Sudden death of entanglement and its rebirth in a system of two nonlinear oscillators

The problem of generating a sudden death and sudden birth of entanglement in a system of two nonlinear oscillators interacting with an external reservoir is presented. The physical mechanism needed for observing these phenomena is indicated. It is found that an external driving field (coupling to one of the nonlinear oscillator modes) can be responsible for entanglement return to the system considered.

Kicked nonlinear quantum scissors and entanglement generation

We consider a nonlinear coupler with two Kerr-like oscillators mutually coupled by continuous linear interaction and excited by a series of ultrashort external pulses. We show that the system behaves like nonlinear quantum scissors. It evolves in such a way that it can be treated as a qubit–qubit system. We derive analytic formulas for the probabilities of the states involved in the systems evolution and show that they differ from those already discussed in the literature and corresponding to the continuously excited models. Moreover, for the model discussed here, maximally entangled Bell states can be generated with high efficiency.

Entanglement between an autoionizing system and a neighboring atom

Entanglement between two electrons belonging to an auto-ionization system and a neighbor two-level atom produced by the dipole-dipole interaction is studied. The entanglement is quantified using the quadratic negativity of a bipartite system including the continuum of states. Suitable conditions for the generation of highly entangled states of two electrons are revealed. Internal structure of the entanglement is elucidated using the spectral density of quadratic negativity.