27 research outputs found
Andreev quantum dot with several conducting channels
We study an Andreev quantum dot, that is a quantum dot inserted in a
superconducting ring, with several levels or conducting channels. We analyze
the degeneracy of the ground state as a function of the phase difference and of
the gate voltage and find its dependence on the Coulomb interaction within and
between channels. We compute a (non integer) charge of the dot region and
Josephson current. The charge-to-phase and current-to-gate voltage
sensitivities are studied. We find that, even in the presence of Coulomb
interaction between the channels, the sensitivity increases with the number of
channels, although it does not scale linearly as in the case with no
interactions. The Andreev quantum dot may therefore be used as a sensitive
detector of magnetic flux or as a Josephson transistor.Comment: 13 pages, 10 figures, minor correction
Nanomechanical effects in an Andreev quantum dot
We consider a quantum dot with mechanical degrees of freedom which is coupled
to superconducting electrodes. A Josephson current is generated by applying a
phase difference. In the absence of coupling to vibrations, this setup was
previously proposed as a detector of magnetic flux and we wish here to address
the effect of the phonon coupling to this detection scheme. We compute the
charge on the quantum dot and determine its dependence on the phase difference
in the presence of phonon coupling and Coulomb interaction. This allows to
identify regions in parameter space with the highest charge to phase
sensitivity, which are relevant for flux detection. Further insight about the
interplay of such couplings and subsequent entanglement properties between
electron and phonon degrees of freedom are gained by computing the von Neuman
entropy.Comment: 9 pages, 7 figures; minor corretion