Optical quantum computation with perpetually coupled spins

The possibility of using strongly and continuously interacting spins for quantum computation has recently been discussed. Here we present a simple optical scheme that achieves this goal while avoiding the drawbacks of earlier proposals. We employ a third state, accessed by a classical laser field, to create an effective barrier to information transfer. The mechanism proves to be highly efficient both for continuous and pulsed laser modes; moreover, it is very robust, tolerating high decay rates for the excited states. The approach is applicable to a broad range of systems, in particular, dense structures such as solid-state self-assembled (e.g., molecular) devices. Importantly, there are existing structures upon which 'first-step' experiments could be immediately performed.