Efficient Universal Leakage Elimination for Physical and Encoded Qubits
  Decoherence-induced leakage errors can couple a physical or encoded qubit to other levels, thus potentially damaging the qubit. They can therefore be very detrimental in quantum computation and require special attention. Here we present a general method for removing such errors by using simple decoupling and recoupling pulse sequences. The proposed gates are experimentally accessible in a variety of promising quantum computing proposals. 
L.-A. Wu, M.S. Byrd, D.A. Lidar (University of Toronto)