The technical demands to perform quantum error correction are considerable.
The task requires the preparation of a many-body entangled state, together with
the ability to make parity measurements over subsets of the physical qubits of
the system to detect errors. Here we propose two trapped-ion experiments to
realise error-correcting codes of variable size to protect a single encoded
qubit from dephasing errors. Novel to our schemes is the use of a global
entangling phase gate, which could be implemented in both Penning traps and
Paul traps. We make use of this entangling operation to significantly reduce
the experimental complexity of state preparation and syndrome measurements. We
also show, in our second scheme, that storage times can be increased further by
repeatedly teleporting the logical information between two codes supported by
the same ion Coulomb crystal to learn information about the locations of
errors. We estimate that a logical qubit encoded in such a crystal will
maintain high coherence for times more than an order of magnitude longer than
each physical qubit would.Comment: 18 pages, 8 figures. The authors list has changed since the first
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