Quantum computation with cold bosonic atoms in an optical lattice

We analyse an implementation of a quantum computer using bosonic atoms in an optical lattice. We show that, even though the number of atoms per site and the tunneling rate between neighbouring sites is unknown, one may perform a universal set of gates by means of adiabatic passage

Controllable coherent population transfers in superconducting qubits for quantum computing

We propose an approach to coherently transfer populations between selected quantum states in one- and two-qubit systems by using controllable Stark-chirped rapid adiabatic passages (SCRAPs). These {\it evolution-time insensitive} transfers, assisted by easily implementable single-qubit phase-shift operations, could serve as elementary logic gates for quantum computing. Specifically, this proposal could be conveniently demonstrated with existing Josephson phase qubits. Our proposal can find an immediate application in the readout of these qubits. Indeed, the broken parity symmetries of the bound states in these artificial "atoms" provide an efficient approach to design the required adiabatic pulses.Comment: 4 pages, 6 figures. to appear in Physical Review Letter

Arbitrary state controlled-unitary gate by adiabatic passage

We propose a robust scheme involving atoms fixed in an optical cavity to directly implement the universal controlled-unitary gate. The present technique based on adiabatic passage uses novel dark states well suited for the controlled-rotation operation. We show that these dark states allow the robust implementation of a gate that is a generalisation of the controlled-unitary gate to the case where the control qubit can be selected to be an arbitrary state. This gate has potential applications to the rapid implementation of quantum algorithms such as of the projective measurement algorithm. This process is decoherence-free since excited atomic states and cavity modes are not populated during the dynamics.Comment: 6 pages, 6 figure, submitted to Phys. Rev.