 is a state. Moreover, the state evolution is linear, i.e., it preserves superpositions: if \(\ket{f,t}\) and \(\ket{g,t}\) are the states obtained by evolving the states \(\ket{f,0}\) and \(\ket{g,0}\), respectively, from the initial time \(t=0\) to the time \(t\), then \(a\ket{f,t} + b\ket{g,t}\) is the state obtained by the evolution of \(a\ket{f,0} + b\ket{g,0}\). Finally, the completeness assumption is made, i.e., that the knowledge of its statevector represents, in principle, the most accurate information one can have about the state of an individual physical system.