Dephasing of electron spin qubits due to their interaction with nuclei in quantum dots

Coherence of spins of electrons confined in III-V quantum dots is strongly affected by their hyperfine interaction with the nuclei. In this paper an introduction to this subject will be given. Some theoretical approaches to the problem will be outlined. Most attention will be given to the Quasi-Static Bath Approximation, to the cluster expansion theories of dephasing due to the nuclear dynamics induced by the dipolar interactions (spectral diffusion), and to the effective Hamiltonian based theory of dephasing due to hyperfine-mediated interactions. The connections between the theoretical results and various experiments will be emphasized.Comment: An invited review, Proceedings of 39th "Jaszowiec" International School and Conference on the Physics of Semiconductors, Krynica 2010, Poland. Journal version available online at http://przyrbwn.icm.edu.pl/APP/ABSTR/119/a119-5-2.htm

The relation between the quantum discord and quantum teleportation: the physical interpretation of the transition point between different quantum discord decay regimes

We study quantum teleportation via Bell-diagonal mixed states of two qubits in the context of the intrinsic properties of the quantum discord. We show that when the quantum-correlated state of the two qubits is used for quantum teleportation the character of the teleportation efficiency changes substantially depending on the Bell-diagonal-state parameters, which can be seen when the worst-case-scenario or best-case-scenario fidelity is studied. Depending on the parameter range, one of two types of single qubit states is hardest/easiest to teleport. The transition between these two parameter ranges coincides exactly with the transition between the range of classical correlation decay and quantum correlation decay characteristic for the evolution of the quantum discord. The correspondence provides a physical interpretation for the prominent feature of the decay of the quantum discord.Comment: 6 page