Transfer of an arbitrary two-qubit pure state with spin chains

We study the transfer of an arbitrary two-qubit pure state with the spin-chain channels and analyze the relevant influences from one common spin environment, asynchronous measurements and imperfect initialization. Since it is not satisfactory enough by directly extending Bose's transfer scheme, we propose and develop an improved dual-rail channel by using two pairs of inhomogenous spin chains one of which is auxiliary. Our results show that the improved scheme can achieve the perfect transfer and greater success probability in a longer distance. In particular, we calculate different influences of the spin environment on different spin-chain channels, and figure out that success probability is not seriously affected by asynchronous measurements, as long as the difference of measurement times on two auxiliary spin chains is small enough. Moreover, the general expression of success probability is also given in the influence of imperfect initialization when the transfer is perfect.