A quantum computer using a trapped-ion spin molecule and microwave radiation

We propose a new design for a quantum information processor where qubits are encoded into Hyperfine states of ions held in a linear array of individually tailored microtraps and sitting in a spatially varying magnetic field. The magnetic field gradient introduces spatially dependent qubit transition frequencies and a type of spin-spin interaction between qubits. Single and multi-qubit manipulation is achieved via resonant microwave pulses as in liquid-NMR quantum computation while the qubit readout and reset is achieved through trapped-ion fluorescence shelving techniques. By adjusting the microtrap configurations we can tailor, in hardware, the qubit resonance frequencies and coupling strengths. We show the system possesses a side-band transition structure which does not scale with the size of the processor allowing scalable frequency discrimination between qubits. By using large magnetic field gradients, one can readout and reset the qubits in the ion chain via frequency selective optical pulses avoiding the need for many tightly focused laser beams for spatial qubit addressing.