Optimal electron entangler at low temperatures

S. Hamieh, Haitham Zaraket

Yu. B. Sherkunov, Jin Zhang, N. d’Ambrumenil +1 more

We show that the equilibrium noise can be dramatically suppressed in the case of a tunnel junction with modulated (time-dependent) transparency. We demonstrate how such a contact could be used either as an optimal electron entangler or as a single-electron source with suppressed equilibrium noise at low temperatures.

Paweł Mazurek, Michał Horodecki, Łukasz Czekaj +1 more

We consider Bayesian estimate of static magnetic field, characterized by a prior Gaussian probability distribution, in systems of a few electron quantum dot spins interacting with infinite temperature spin environment via hyperfine interaction. Sudden transitions among optimal states and measurements are observed. Usefulness of measuring occupation levels is shown for all times of the evolution, together with the role of entanglement in the optimal scenario. For low values of magnetic field, memory effects stemming from the interaction with environment provide limited metrological advantage.

William D. Oliver

S. Hamieh, Haitham Zaraket

Tomotaka Kuwahara, Naomichi Hatano

We investigate the thermal entanglement of interacting two qubits. We maximize it by tuning a local Hamiltonian under a given interaction Hamiltonian. We prove that the optimizing local Hamiltonian takes a simple form which does not depend on the temperature and that the corresponding optimized thermal entanglement decays as $1/(T\mathrm{ln}T)$ at high temperatures. We also find that at low temperatures the thermal entanglement is maximum without any local Hamiltonians and that the second derivative of the maximized thermal entanglement changes discontinuously at the boundary between the high- and low-temperature phases.