  Spin ensemble based hybrid quantum systems suffer from a significant degree
of decoherence resulting from the inhomogeneous broadening of the spin
transition frequencies in the ensemble. We demonstrate that this strongly
restrictive drawback can be overcome simply by burning two narrow spectral
holes in the spin spectral density at judiciously chosen frequencies. Using
this procedure we find an increase of the coherence time by more than an order
of magnitude as compared to the case without hole burning. Our findings pave
the way for the practical use of these hybrid quantum systems for the
processing of quantum information.
