Optical schemes for quantum computation in quantum dot molecules

We give three methods for entangling quantum states in quantum dots. We do this by showing how to tailor the resonant energy (Forster-Dexter) transfer mechanisms and the biexciton binding energy in a quantum dot molecule. We calculate the magnitude of these two electrostatic interactions as a function of dot size, interdot separation, material composition, confinement potential, and applied electric field by using an envelope function approximation in a two-cuboid dot molecule. In the first implementation, we show that it is desirable to suppress the Forster coupling and to create entanglement by using the biexciton energy alone. We show how to perform universal quantum logic in a second implementation which uses the biexciton energy together with appropriately tuned laser pulses: by selecting appropriate material parameters high-fidelity logic can be achieved. The third implementation proposes generating quantum entanglement by switching the Forster interaction itself. We show that the energy transfer can be fast enough in certain dot structures that switching can occur on a time scale which is much less than the typical decoherence times.