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The concept of time evolution may be applicable to other stateful systems as well. For instance, the operation of a Turing machine can be regarded as the time evolution of the machine's control state together with the state of the tape (or possibly multiple tapes) including the position of the machine's read-write head (or heads). In this case ...
Time evolution described by a time-independent Hamiltonian is represented by a one-parameter family of unitary operators, for which the Hamiltonian is a generator: () = ^ /. In the Schrödinger picture , the unitary operators are taken to act upon the system's quantum state, whereas in the Heisenberg picture , the time dependence is ...
Note that the Hamiltonian that appears in the final line above is the Heisenberg Hamiltonian (), which may differ from the Schrödinger Hamiltonian (). An important special case of the equation above is obtained if the Hamiltonian H S {\displaystyle H_{\rm {S}}} does not vary with time.
If the Hamiltonian has explicit time-dependence (for example, if the quantum system interacts with an applied external electric field that varies in time), it will usually be advantageous to include the explicitly time-dependent terms with ,, leaving , time-independent. We proceed assuming that this is the case.
In quantum mechanics, the Schrödinger equation describes how a system changes with time. It does this by relating changes in the state of the system to the energy in the system (given by an operator called the Hamiltonian). Therefore, once the Hamiltonian is known, the time dynamics are in principle known.
The Hamiltonian of a system represents the total energy of the system; that is, the sum of the kinetic and potential energies of all particles associated with the system. . The Hamiltonian takes different forms and can be simplified in some cases by taking into account the concrete characteristics of the system under analysis, such as single or several particles in the system, interaction ...
where the interaction-picture perturbation Hamiltonian becomes a time-dependent Hamiltonian, unless [H 1,S, H 0,S] = 0. It is possible to obtain the interaction picture for a time-dependent Hamiltonian H 0,S ( t ) as well, but the exponentials need to be replaced by the unitary propagator for the evolution generated by H 0,S ( t ), or more ...
Thus, the time evolution of a function on a symplectic manifold can be given as a one-parameter family of symplectomorphisms (i.e., canonical transformations, area-preserving diffeomorphisms), with the time being the parameter: Hamiltonian motion is a canonical transformation generated by the Hamiltonian.