Conclusive and arbitrarily perfect quantum-state transfer using parallel spin-chain channels

We suggest a protocol for perfect quantum communication through spin-chain channels. By combining a dual-rail encoding with measurements only at the receiving end, we can get conclusively perfect state transfer, whose probability of success can be made arbitrarily close to unity. As an example of such an amplitude-delaying channel, we show how two parallel Heisenberg spin chains can be used as quantum wires. Perfect state transfer with a probability of failure lower than P in a Heisenberg chain of N spin-1/2 particles can be achieved in a timescale of the order of (0.33h/J)N-1.7\ln P\. We demonstrate that our scheme is more robust to decoherence and nonoptimal timing than any scheme using single spin chains.