Recently, de Visser and Blaauboer [Phys. Rev. Lett. {bf 96}, 246801 (2006)] proposed the most efficient deterministic teleportation protocol $cal T$ for electron spins in a semiconductor nanostructure consisting of a single and a double quantum dot.
However, it is as yet unknown if $cal T$ can be completed before decoherence sets in. In this paper we analyze the detrimental effect of nuclear spin baths, the main source of decoherence, on $cal T$. We show that nonclassical teleportation fidelity can be achieved with $cal T$ provided certain conditions are met. Our study indicates that realization of quantum computation with quantum dots is indeed promising.
Recently, Zhang {em et al.} [PRA, {bf 75}, 062102 (2007)] extended Kieus interesting work on the quantum Otto engine [PRL, {bf 93}, 140403 (2004)] by considering as working substance a bipartite quantum system $AB$ composed of subsystems $A$ and $B$.
In this paper, we express the net work done $W_{AB}$ by such an engine explicitly in terms of the macroscopic bath temperatures and information theoretic quantities associated with the microscopic quantum states of the working substance. This allows us to gain insights into the dependence of positive $W_{AB}$ on the quantum properties of the states. We illustrate with a two-qubit XY chain as the working substance. Inspired by the expression, we propose a plausible formula for the work derivable from the subsystems. We show that there is a critical entanglement beyond which it is impossible to draw positive work locally from the individual subsystems while $W_{AB}$ is positive. This could be another interesting manifestation of quantum nonlocality.
