Possible realization of an ideal quantum computer
in Josephson junction array.
Mikhail V. Feigel'man2 (

) and L. B. Ioffe
1,2 (

)
1Center for Materials Theory,
Department of Physics and Astronomy, Rutgers University,
136 Frelinghuysen Rd, Piscataway NJ 08854, USA
2D.Landau Institute for Theoretical Physics, Kosygina 2,
Moscow, 117940 Russia.
We introduce a new class of Josephson arrays which have non-trivial topology
and
exhibit a novel state at low temperatures. This state is characterized by
long range order in a two Cooper pair condensate and by a discrete topological
order parameter. These arrays have degenerate ground states with
this degeneracy 'protected' from the external perturbations (and noise) by the
topological
order parameter. We show that in ideal conditions the low order effect of the
external perturbations on this degeneracy is exactly zero and that deviations
from ideality
lead to only exponentially small effects of perturbations. We argue that this
system provides
a physical implementation of an ideal quantum computer with a built in error
correction and
show that even a small array exhibits interesting physical properties such as
superconductivity
with double charge, 4e, and extremely long decoherence times.