  A scheme for concatenating the recently invented polar codes with interleaved
block codes is considered. By concatenating binary polar codes with interleaved
Reed-Solomon codes, we prove that the proposed concatenation scheme captures
the capacity-achieving property of polar codes, while having a significantly
better error-decay rate. We show that for any $\epsilon > 0$, and total frame
length $N$, the parameters of the scheme can be set such that the frame error
probability is less than $2^{-N^{1-\epsilon}}$, while the scheme is still
capacity achieving. This improves upon $2^{-N^{0.5-\eps}}$, the frame error
probability of Arikan's polar codes. We also propose decoding algorithms for
concatenated polar codes, which significantly improve the error-rate
performance at finite block lengths while preserving the low decoding
complexity.
