  Contrary to the assumption that most quantum error-correcting codes (QECC)
make, it is expected that phase errors are much more likely than bit errors in
physical devices. By employing the entanglement-assisted stabilizer formalism,
we develop a new kind of error-correcting protocol which can flexibly trade
error correction abilities between the two types of errors, such that high
error correction performance is achieved both in symmetric and in asymmetric
situations. The characteristics of the QECCs can be optimized in an adaptive
manner during information transmission. The proposed entanglement-assisted
QECCs require only one ebit regardless of the degree of asymmetry at a given
moment and can be decoded in polynomial time.
