The coherent control of molecular processes by extremely short laser pulses and the rapid switching of electronic devices provide two important areas in which transient quantum mechanical processes play vital roles. By varying the frequency and temporal characteristics of a laser pulse impinging on a molecule, one can produce different mixtures of interacting quantum states and therefore exert control on the dynamical reponse of the molecule. In addition, rapid microswitching in nanostructures (such as quantum dots) arises from the temporal control of electrons through composition changes in materials.
Studying these phenomena requires the solution of the time-dependent Schrodinger equation that governs these transient mechanisms. The solutions of these equations may demand we include a large number of quantum states and follow the dynamics of these states for long times. For this reason, we are developing physical models to describe the molecular and structural interactions involved, and we are developing quantum computational techniques to follow these processes.
For simple, one-dimensional systems (e.g., slowly-rotating diatomic molecules), we are developing a quantum wavepacket evolution code, based upon using the DVR (discrete variable representation) method to define basis functions for the vibrational bound states of each of the involved electronic states the molecule. THE DVR method permits an extremely straightforward representation of both the kinetic and potential energy parts of the time-dependent Hamiltonian for the system.
Current applications are being made to experiments here at LANL on the pumping of potassium dimers using femtosecond pulses. We'll get some results of these calculations ready to show soon.