A repetition code of 15 qubits. (arXiv:1709.00990v2 [quant-ph] UPDATED)

The repetition code is an important primitive for the techniques of quantum
error correction. Here we implement repetition codes of at most $15$ qubits on
the $16$ qubit \emph{ibmqx3} device. Each experiment is run for a single round
of syndrome measurements, achieved using the standard quantum technique of
using ancilla qubits and controlled operations. The size of the final syndrome
is small enough to allow for lookup table decoding using experimentally
obtained data. The results show strong evidence that the logical error rate
decays exponentially with code distance, as is expected and required for the
development of fault-tolerant quantum computers. The results also give insight
into the nature of noise in the device.

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