  Quantum communication over long distances relies on the ability to create
entanglement between two remote quantum nodes. Recent proposals aiming at
experimental realization propose a hybrid quantum repeater setup where two
distant material qubits are entangled by light-matter interaction. Motivated by
these developments, we investigate possible decoherence effects originating
from the centre- of-mass motion of the spatially well separated trapped qubits.
Within the Lamb-Dicke regime we use photon exchange involving coherent states
of the radiation field to entangle the two material qubits. Optimal generalized
photonic field measurements are used to achieve entangled qubit pairs with high
fidelities and high success probabilities. We demonstrate that the quality of
the achievable two-qubit entanglement crucially depends on the trap frequencies
involved. Furthermore, dynamical decoupling schemes are proposed which are
capable of suppressing centre-of-mass-motion-induced decoherence effects
significantly and which involve only local operations acting on the spatially
well-separated material qubits.
