  Optically connecting quantum bits can effectively reduce decoherence and
facilitate long-distance communication. Optically addressable spin-bearing
molecules have been demonstrated to have a good potential for quantum
computing. In this report optically induced exchange interactions and spin
dynamics, which are inherently important for spin-based quantum computing, have
been calculated for a bi-radical - a potential quantum computing circuit unit.
Consistent with the previous experimental observation of spin coherence induced
by optical excitation, our work demonstrated an optically driven quantum gate
operation scheme, implying a great potential of molecular quantum-circuit
network. A blueprint of quantum circuit, integrating two-dimensional molecular
network and programmable nano-photonics, both of which have been under
extensive investigations and rather mature, was proposed. We thus envisage
computational exploration of chemical database to identify suitable candidates
for molecular spin quantum bit and coupler, which could be optimally integrated
with nano-photonic devices to realize quantum circuit. The work presented here
would therefore open up a new direction to explore 'Click Chemistry' for
quantum technology.
