High-fidelity Z -measurement error encoding of optical qubits

We demonstrate a quantum error correction scheme that protects against accidental measurement, using a parity encoding where the logical state of a single qubit is encoded into two physical qubits using a nondeterministic photonic controlled-NOT gate. For the single qubit input states ∣0⟩ , ∣1⟩ , ∣0⟩±∣1⟩ , and ∣0⟩±i∣1⟩ our encoder produces the appropriate two-qubit encoded state with an average fidelity of 0.88±0.03 and the single qubit decoded states have an average fidelity of 0.93±0.05 with the original state. We are able to decode the two-qubit state (up to a bit flip) by performing a measurement on one of the qubits in the logical basis; we find that the 64 one-qubit decoded states arising from 16 real and imaginary single-qubit superposition inputs have an average fidelity of 0.96±0.03 .