Ch 2.6 The vector $\mathbf{j} = \frac{\hbar}{2mi}(\psi^*\nabla\psi - \psi\nabla\psi^*)$ satisfying the continuity equation $\partial|\psi|^2/\partial t + \nabla\cdot\mathbf{j} = 0$. Ensures conservation of probability. *See also:* Continuity equation, Wave function, Normalization.