Swapan Kumar Das’s research while affiliated with Maulana Azad College and other places

The significance of Ehrenfest Theorem in quantum-classical relationship is discussed in terms of the general formulation of the theorem. With the ensemble interpretation of the quantum mechanical $\Psi$-function the Generalised Ehrenfest Theorem reveals some interesting exact relationships between quantum- and classical expectation values. These general results seem to imply a deep rooted unity (inspite of apparent radical differences in conceptual structures) between classical and quantum mechanics. Some significant consequences and important physical insights which follow from the general formulation are discussed with examples. Most important is that it offers, under reasonable approximations, a pure quantum mechanical description of the Stern-Gerlach experiment with realistic inhomogeneous magnetic field $(\nabla.{\bf B} = 0)$.