  The field-induced antiferromagnetic ordering in systems of weakly coupled
S=1/2 dimers at zero temperature can be described as a Bose-Einstein
condensation of triplet quasiparticles (singlet quasiholes) in the ground
state. For the case of a Heisenberg bilayer, it is here shown how the above
picture is altered in the presence of site dilution of the magnetic lattice.
Geometric randomness leads to quantum localization of the
quasiparticles/quasiholes and to an extended Bose-glass phase in a realistic
disordered model. This localization phenomenon drives the system towards a
quantum-disordered phase well before the classical geometric percolation
threshold is reached.
