MIXED INTERNAL-EXTERNAL STATE APPROACH FOR QUANTUM COMPUTATION WITH NEUTRAL ATOMS ON ATOM CHIPS E. CHARRON Laboratoire de Photophysique Moléculaire du CNRS, Bâtiment 210, Université Paris-Sud 11, 91405 Orsay cedex, France M. A. CIRONE ECT*, Strada delle Tabarelle 286, I-38050 Villazzano, Trento, Italy Dipartimento di Fisica, Università di Trento and BEC-CNR-INFM, I-38050 Povo, Italy A. NEGRETTI ECT*, Strada delle Tabarelle 286, I-38050 Villazzano, Trento, Italy Dipartimento di Fisica, Università di Trento and BEC-CNR-INFM, I-38050 Povo, Italy Institut für Physik Universität Potsdam Am Neuen Palais 10, 14469 Potsdam, Germany J. SCHMIEDMAYER Physikalisches Institut, Universtät Heidelberg, Am Neuen Palais 10, 14469 Potsdam Germany T. CALARCO ECT*, Strada delle Tabarelle 286, I-38050 Villazzano, Trento, Italy Dipartimento di Fisica, Università di Trento and BEC-CNR-INFM, I-38050 Povo, Italy ITAMP and Department of Physics, Harvard University, Cambridge, MA 02138, USA We present a realistic proposal for the storage and processing of quantum information with cold 87 Rb atoms on atom chips. The qubit states are stored in hyperfine atomic levels with long coherence time, and two-qubit quantum phase gates are realized using the motional states of the atoms. Two-photon Raman transitions are used to transfer the qubit information from the internal to the external degree of freedom. The quantum phase gate is realized in a double-well potential created by slowly varying dc currents in the atom chip wires. Using realistic values for all experimental parameters (currents, magnetic fields, ...) we obtain high gate fidelities (above 99.9%) in short operation times (~ 10 ms). 1. Introduction Beyond their fundamental interest in physics, coherence and entanglement of quantum states are the building blocks of quantum information 1 . Performing very simple operations on a limited number of qubits is a real experimental 1