  The principle of superposition is an intriguing feature of Quantum Mechanics,
which is regularly exploited at various instances. A recent work [PRL
\textbf{116}, 110403 (2016)] shows that the fundamentals of Quantum Mechanics
restrict the superposition of two arbitrary pure states of a quantum system,
even though it is possible to superpose two quantum states with partial prior
knowledge. The prior knowledge imposes geometrical constraints on the choice of
input pure states. We discuss an experimentally feasible protocol to superpose
multiple pure states of a $d$ dimensional quantum system and carry out an
explicit experimental realization to superpose two single-qubit pure states on
a two-qubit NMR quantum information processor.
