Scheme for direct measurement of a general two-qubit Hamiltonian

The construction of two-qubit gates appropriate for universal quantum computation is of enormous importance to quantum-information processing. Building such gates is dependent on accurate knowledge of the interaction dynamics between two-qubit systems. This paper will present a systematic method for reconstructing the full two-qubit interaction Hamiltonian through experimental measures of concurrence. This not only gives a convenient method for constructing two qubit quantum gates, but can also be used to experimentally determine various Hamiltonian parameters in physical systems. We show explicitly how this method can be employed to determine the first- and second-order spin-orbit corrections to the exchange coupling in quantum dots.