Sudden Death and Birth of Entanglement Effects for Kerr-Nonlinear Coupler

We analyse the entanglement dynamics in a nonlinear Kerr-like coupler interacting with external environment. Whenever the reservoir is in a thermal vacuum state the entanglement (measured by concurrence for a two-qubit system) exhibits regular oscillations of decreasing amplitude. In contrast, for thermal reservoirs we can observe dark periods in concurrence oscillations (which can be called a "sudden death" of the entanglement) and the entanglement rebuild (which can be named the "sudden birth" of entanglement). We show that these features can be observed when we deal with 2-qubit system as well as $2\otimes 3$ system.Comment: 18 pages including 7 figures. Journal of the Optical Society of America B - in pres

Finite-dimensional states and entanglement generation for a nonlinear coupler

We discuss a system comprising two nonlinear (Kerr-like) oscillators coupled mutually by a nonlinear interaction. The system is excited by an external coherent field that is resonant to the frequency of one of the oscillators. We show that the coupler evolution can be closed within a finite set of $n$-photon states, analogously as in the \textit{nonlinear quantum scissors} model. Moreover, for this type of evolution our system can be treated as a \textit{Bell-like states} generator. Thanks to the nonlinear nature of both: oscillators and their internal coupling, these states can be generated even if the system exhibits its energy dissipating nature, contrary to systems with linear couplings.Comment: Accepted for publication in Physical Review

Long-time fidelity and chaos for a kicked nonlinear oscillator system

We deal with a system comprising a nonlinear (Kerr-like) oscillator excited by a series of ultra-short external pulses. We introduce the fidelity-based entropic parameter that can be used as an indicator of quantum chaos. Moreover, we propose to use the fidelity-like parameter comprising the information about the mean number of photons in the system. We shall concentrate on the long-time behaviour of the parameters discussed, showing that for deep chaos cases the quantum fidelities behave chaotically in the classical sense despite their strictly quantum character.Comment: 20 pages including 8 figure