  We have studied theoretically the basic operation of a quantum feedback loop
designed to maintain a desired phase of quantum coherent oscillations in a
single solid-state qubit. The degree of oscillations synchronization with
external harmonic signal is calculated as a function of feedback strength,
taking into account available bandwidth and coupling to environment.
  The feedback can efficiently suppress the dephasing of oscillations if the
qubit coupling to the detector is stronger than coupling to environment.
