Encoding a logical qubit into physical qubits

We propose two protocols to encode a logical qubit into physical qubits relying on common types of qubit-qubit interactions in as simple forms as possible. We comment on its experimental implementation in several quantum computing architectures, e.g., with trapped atomic ion qubits, atomic qubits inside a high-Q optical cavity, solid-state Josephson junction qubits, and Bose-Einstein condensed atoms