Quantum coherence in a coupled exciton-quantum-dot system

Summary form only given. Optically driven semiconductor quantum dots (QD's) are of interest in many areas of opto-electronic devices as well as featuring prominently in many proposals for quantum computing. The necessary component of a scalable quantum computer, the two-qubit logic gate, requires two separate yet interacting qubits. In QD's, this is a multi-exciton state. Recently the bound state of two-excitons (the biexciton) has been successfully created and studied using nonlinear spectroscopy. We report here high resolution coherent nonlinear optical spectroscopy showing spectral features that are distinct from the biexcitonic features but similar to that expected for a coupled two exciton system. The spectroscopic results are interpreted based on a phenomenological Hamiltonian which is consistent with the excitons being confined but interacting in an antibonding state, where the excitons are most likely separately localized.