Searcharxiv⌕ Search

arXiv subjects

L. Derkacz

Publications and source records attributed to L. Derkacz.

7 recordsLinked to original sources
arXiv2011

Entanglement beyond tensor product structure: algebraic aspects of quantum non - separability

Algebraic approach to quantum non - separability is applied to the case of two qubits. It is based on the partition of the algebra of observables into independent subalgebras and the tensor product structure of the Hilbert space is not exploited. Even in this simple case, such general formulation has some advantages. Using algebraic formalism we can explicitly show the relativity of the notion of entanglement to the observables measured in the system and characterize separable and non - separable pure states. As a universal measure of non - separability of pure states we propose to take so called total correlation. This quantity depends on the state as well as on the algebraic partition. Its numerical value is given by the norm of the corresponding correlation matrix

quant-ph↗
arXiv2008

Dynamical creation of entanglement versus disentanglement in a system of three - level atoms with vacuum - induced coherences

The dynamics of entanglement between three - level atoms coupled to the common vacuum is investigated. We show that the collective effects such as collective damping, dipole - dipole interaction and the cross coupling between orthogonal dipoles, play a crucial role in the process of creation of entanglement. In particular, the additional cross coupling enhances the production of entanglement. For the specific initial states we find that the effect of delayed sudden birth of entanglement, recently invented by Ficek and Tanas [Phys. Rev. A 77, o54301(2008)] in the case of two - level atoms, can also be observed in the system. When the initial state is entangled, the process of spontaneous emission causes destruction of correlation and its disentanglement. We show that the robustness of initial enatnglement against the noise can be changed by local operations performed on the state.

quant-ph↗
arXiv2006

Quantum interference and evolution of entanglement in a system of three-level atoms

We consider a pair of three-level atoms interacting with the vacuum. The process of disentanglement due to spontaneous emission and the role of quantum interference between principal transitions in this process, are analysed. We show that the presence of interference can slow down disentanglement. In the limit of maximal interference, some part of initial entanglement can survive.

quant-ph↗
arXiv2005

CHSH violation and entropy - concurrence plane

We characterize violation of CHSH inequalities for mixed two-qubit states by their mixedness and entanglement. The class of states that have maximum degree of CHSH violation for a given linear entropy is also constructed.

quant-ph↗
arXiv2004

Bell inequalities versus entanglement and mixedness for a class of two - qubit states

For a class of mixed two -qubit states we show that it is not possible to discriminate between states violating or non - violating Bell - CHSH inequalities, knowing only their entanglement and mixedness. For a large set of possible values of these quantities, we construct pairs of states with the same entanglement and mixedness such that one state is violating but the other is non - violating Bell - CHSH inequality.

quant-ph↗