Quantum gates with atomic ensembles on an atom chip

We propose a scheme for implementing quantum computation with atomic ensembles on an atom chip, where a single qubit is carried by an atomic ensemble instead of a single atom. Two electronic ground states of the atoms are involved, one state with one or no atom is used to represent the qubit and the other state is used to hold the residual atoms. One and two-qubit gates are implemented by internal state transition with laser pulse sequences in the presence of the exciting blockade mechanism. A scalable quantum computer can be realized by one-dimensional or two-dimensional atomic lattices on an atom chip.