  The major contribution to decoherence of a double quantum dot or a Josephson
junction charge qubit comes from the electrostatic coupling to fluctuating
background charges hybridized with the conduction electrons in the reservoir.
However, estimations according to previously developed theories show that
finding a sufficient number of effective fluctuators in a realistic
experimental layout is quite improbable. We show that this paradox is resolved
by allowing for a short-range Coulomb interaction of the fluctuators with the
electrons in the reservoir. This dramatically enhances both the number of
effective fluctuators and their contribution to decoherence, resulting in the
most dangerous decoherence mechanism for charge qubits.
