Schrödinger revisited: the role of Dirac’s ‘standard’ ket in the algebraic approach.

We follow Dirac and write the Schrödinger equation in an algebraic form which is representation-free. The imaginary and real parts of this equation are respectively the Liouville equation, which involves the commutator of the Hamiltonian with the density operator and an equation for the time development of the phase operator that involves the anti-commutator of the Hamiltonian with the density operator. We show this latter equation plays two important roles: (i) it expresses the conservation of energy in a system where energy is well defined and (ii) it provides a simple way to evaluate the gauge changes that occur in the Aharonov-Bohm, the Aharonov-Casher, and Berry phase effects. Both these operator (i.e. purely algebraic) equations also allow us to reexamine the Bohm interpretation, showing that it is in fact possible to construct Bohm interpretations in representations other than the x-representation. We discuss the meaning of the Bohm interpretation in the light of these new results in terms of non-commutative structures and this enables us to clarify its relation to standard quantum mechanics.