  The problem of finding and characterizing minimal sets of dequantizers and
quantizers applied in the mapping of operators onto functions is considered,
for finite-dimensional quantum systems. The general properties of such sets are
determined. An explicit description of all the minimum self-dual sets of
dequantizers and quantizers for a qubit system is derived. The connection
between some known sets of dequantizers and quantizers and the derived formulae
is presented.
