  An increase in the quality factor of superconducting radiofrequency cavities
is achieved by minimizing the surface resistance during processing steps. The
surface resistance is the sum of temperature independent residual resistance
and temperature/material dependent Bardeen-Cooper-Schrieffer (BCS) resistance.
High temperature heat treatment usually reduces the impurities concentration
from the bulk niobium, lowering the residual resistance. The BCS part can be
reduced by selectively doping non-magnetic impurities. The increase in quality
factor, termed as Q-rise, was observed in cavities when titanium or nitrogen
thermally diffused in the inner cavity surface.
