  Superconducting, flux-based qubits are promising candidates for the
construction of a large scale quantum computer. We present an explicit quantum
mechanical calculation of the coherent behavior of a flux based quantum bit in
a noisy experimental environment such as an integrated circuit containing bias
and control electronics. We show that non-thermal noise sources, such as bias
current fluctuations and magnetic coupling to nearby active control circuits,
will cause decoherence of a flux-based qubit on a timescale comparable to
recent experimental coherence time measurements.
