Global optical control of a quantum spin chain

Quantum processors that combine the long decoherence times of spin qubits together with fast optical manipulation of excitons have recently been the subject of several proposals. Here, I show that arbitrary single-and entangling two-qubit gates can be performed in a chain of perpetually coupled spin qubits solely by using laser pulses to excite higher lying states. It is also demonstrated that universal QC is possible even if these pulses are applied globally to a chain; by employing a repeating pattern of four distinct qubit units, the need for individual qubit addressing is removed. Some current experimental qubit systems would lend themselves to implementing this idea.