Quantum error correction with mixed ancilla qubits

摘要

Most quantum error-correcting codes are predicated on the assumption that there exists a reservoir of qubitsnin the state |0u0002 which can be used as ancilla qubits to prepare multiqubit logical states. In this Brief Report, wenexamine the consequences of relaxing this assumption and propose amethod to increase the fidelity produced by angiven code when the ancilla qubits are initialized in mixed states, using the same number of qubits, at most doublingnthe number of gates when the recovery operation would already be implemented. The procedure implementednconsists of altering the encoding operator to include the inverse of the unitary operation used to correct detectednerrors after decoding. This augmentation will be especially useful in quantum computing architectures that donnot possess projective measurement, such as solid-state NMR quantum information processing.