Terry Rudolph explains the advantages of using photons as a basis for quantum computers.
From the abstract:
Physical advantages to building a quantum computer out of optical frequency photons include: they suffer negligible environment decoherence even at room temperature, there is no cross talk, they network easily into arbitrary geometries, the relevant physics is not heuristic and is often both efficiently simulatable and verifiable with classical light, and measurements – the critical element for entropy reduction to achieve fault tolerance – are sharp and extremely fast. However these pale in comparison to the engineering advantages: all parts of the machine can be built in a tier-1 foundry, and packaged in the same back-end-of-line processes used to build laptops and cellphones. Thus with photons we can realistically stare down the sorts of numbers (~1 million qubits) which capture the size of machine required to do useful quantum computation.