Polarons in suspended carbon nanotubes.

We prove theoretically the possibility of electric-field controlled polaron formation involving flexural (bending) modes in suspended carbon nanotubes. Upon increasing the field, the ground state of the system with a single extra electron undergoes a first-order phase transition between an extended state and a localized polaron state. For a common experimental setup, the threshold electric field is only of the order of approximately equal 5×10(-2) V/µm.

Polarization of a charge qubit strongly coupled to a voltage-driven quantum point contact.

We study a charge qubit with level splitting epsilon, coupled to a quantum point contact driven by voltage V. In the limit of weak coupling, the qubit polarization shows cusps at epsilon=+/-eV. We show that, for stronger couplings, prominent peculiarities occur at fractions epsilon=+/-eV/2. Further increase of the coupling leads to a polarization corresponding to a pseudo Boltzmann distribution with an effective temperature approximately eV.

Quantum tunneling detection of two-photon and two-electron processes.

We analyze the operation of a quantum tunneling detector coupled to a coherent conductor. We demonstrate that, in a certain energy range, the output of the detector is determined by two-photon processes, two-interacting-electron processes, and the interference of the two. We show how the individual contributions of these processes can be resolved in experiments.