Codes for the Quantum Erasure Channel
  The quantum erasure channel (QEC) is considered. Codes for the QEC have to correct for erasures, i. e., arbitrary errors at known positions. We show that four qubits are necessary and sufficient to encode one qubit and correct one erasure, in contrast to five qubits for unknown positions. Moreover, a family of quantum codes for the QEC, the quantum BCH codes, that can be efficiently decoded is introduced. 
Markus Grassl (1), Thomas Beth (1), Thomas Pellizzari (2) ((1)   Universitaet Karlsruhe, (2) Universitaet Innsbruck)