Figure 3: Loss tolerance.
From: Experimental demonstration of a graph state quantum error-correction code
(a) General scenario of loss tolerance for the four-qubit graph code. Here any one of the four qubits may be lost. In the first case, qubit 4 has been lost by combining the two paths corresponding to the computational basis of the qubit. The encoded qubit can be recovered on qubit 1 using the measurements and results of the remaining qubits 2 and 5 as described in the main text. (b) Path qubit lost with the recovery treated as a channel. Here the Bloch sphere representation is used to show the original qubit states and the recovered qubit states. (c) The χ matrix representation of the channel, showing the real part (left) and imaginary part (right). Ideally the χ matrix has only one component, the entry I I, corresponding to the identity operation. (d) In the second case, qubit 1 has been lost by combining the two polarizations corresponding to the computational basis of the qubit. The encoded qubit is recovered on qubit 5 using the measurements and results of the remaining qubits 2 and 4. (e) Polarization qubit loss with the recovery treated as a channel. Here the Bloch sphere representation shows the original qubit states and the recovered qubit states. (f) The χ matrix representation of the channel, showing the real part (left) and imaginary part (right).
