Concatenated Codes for Amplitude Damping
  We discuss a method to construct quantum codes correcting amplitude damping errors via code concatenation. The inner codes are chosen as asymmetric Calderbank-Shor-Steane (CSS) codes. By concatenating with outer codes correcting symmetric errors, many new codes with good parameters are found, which are better than the amplitude damping codes obtained by any previously known construction. 
Tyler Jackson, Markus Grassl and Bei Zeng
quant-ph