  A new experimental realization of heat capacity as an entanglement witness
(EW) is reported. Entanglement properties of a low dimensional quantum spin
system are investigated by heat capacity measurements performed down to very
low temperatures (400mK), for various applied magnetic field values. The
experimentally extracted results for the value of heat capacity at zero field
matches perfectly with the theoretical estimates of entanglement from model
Hamiltonians. The studied sample is a spin $\frac{1}{2}$ antiferromagnetic
system which shows clear signature of quantum phase transition (QPT) at very
low temperatures when the heat capacity is varied as a function of fields at a
fixed temperature. The variation of entanglement as a function of field is then
explored in the vicinity of the quantum phase transition to capture the sudden
loss of entanglement.
