  Experimental realization of magnetic field induced quantum phase transition
(QPT) is reported for NH4CuPO4.H2O, a two spin cluster material with isotropic
Heisenberg interaction. Experimental magnetization and specific heat data have
been collected as a function of temperature and magnetic field. Experimental
data have been analyzed in terms of Heisenberg dimer model. Two quantum
complementary observables representing local and non-local properties of the
spins are constructed using the experimental data and a clear evidence of QPT
is observed through partial quantum information sharing when the magnetic field
is swept through a particular value. Signature of QPT is also observed when
specific heat is measured as a function of magnetic field at low temperature.
Furthermore, using the experimental specific heat data, magnetic energy values
are calculated and their variations are captured as a function of magnetic
field and temperature.
