Macroscopic quantum teleportation with ensembles of qubits

We develop methods for performing quantum teleportation of the total spin
variables of an unknown state, using quantum nondemolition measurements, spin
projection measurements, and classical communication. While theoretically
teleportation of high-dimensional states can be attained with the assumption of
generalized Bell measurements, this is typically experimentally non-trivial to
implement. We introduce two protocols and show that, on average, the
teleportation succeeds in teleporting the spin variables of a spin coherent
state with average zero angular error in the ideal case, beating classical
strategies based on quantum state estimation. In a single run of the
teleportation, there is an angular error at the level of ~ 0.1 radians for
large ensembles. A potential physical implementation for the scheme is with
atomic ensembles and quantum nondemolition measurements performed with light.
We analyze the decoherence of the protocols and find that the protocol is
robust even in the limit of large ensemble sizes.