  Any pure two-qubit state can be represented by six real angles, with a
natural parameterization indicated by the bipartite structure. After explicitly
identifying all of these angles for the first time, it is found that the
parameters can always be completely separated into two "dynamically local"
spinor components. Specifically, given local Hamiltonians at the locations of
the two qubits, unitary dynamics on each spinor can be implemented separately
without losing any entanglement information in the full state. Such a
conclusion also follows from a phase-fixed version of the Schmidt
decomposition.
