2 research outputs found
Mediated tunable coupling of flux qubits
It is sketched how a monostable rf- or dc-SQUID can mediate an inductive
coupling between two adjacent flux qubits. The nontrivial dependence of the
SQUID's susceptibility on external flux makes it possible to continuously tune
the induced coupling from antiferromagnetic (AF) to ferromagnetic (FM). In
particular, for suitable parameters, the induced FM coupling can be
sufficiently large to overcome any possible direct AF inductive coupling
between the qubits.
The main features follow from a classical analysis of the multi-qubit
potential. A fully quantum treatment yields similar results, but with a
modified expression for the SQUID susceptibility.
Since the latter is exact, it can also be used to evaluate the
susceptibility--or, equivalently, energy-level curvature--of an isolated
rf-SQUID for larger shielding and at degenerate flux bias, i.e., a (bistable)
qubit. The result is compared to the standard two-level (pseudospin) treatment
of the anticrossing, and the ensuing conclusions are verified numerically.Comment: REVTeX 4, 16 pp., 4 EPS figures. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: major expansion and rewriting,
new title and co-author; to appear in New Journal of Physics special issue
(R. Fazio, ed.