ABSTRACT
A formalism which is equivalent to the preceding stationary treatment is provided by the time-dependent Schrödinger equation. In the Schrödinger picture of quantum mechanics, operators are stationary and wave functions are time-dependent. The term ‘transient’ usually refers to a time developing phenomenon which dies out after a sufficiently long time lag has elapsed. Such are the envelopes of experimentally encoded time signals as a linear combination of damped exponentials with constant amplitudes such that all complex frequencies must have the negative imaginary parts. A more general meaning of the term transient in sequence-to-sequence transformations has been encountered in quantum-mechanical signal processing. The term unstable or secular transients has been used whenever referring to a time signal in which one or more fundamental frequencies are exponentially diverging. Any finite or infinite sum of harmonics would diverge if at least one of the complex fundamental frequencies is secular.
