Extended Data Fig. 8: Preparation of logical Bell state.

a, Quantum circuit for preparing the logical Bell state \({| \mathop{0}\limits^{ \sim }\rangle }_{{\rm{L}}}{| \mathop{0}\limits^{ \sim }\rangle }_{{\rm{R}}}+{\rm{i}}{| \mathop{1}\limits^{ \sim }\rangle }_{{\rm{L}}}{| \mathop{1}\limits^{ \sim }\rangle }_{{\rm{R}}}\). The CZ gate applied on two edge qubits Q₁ and Q₁₀₀ is local as the two edge qubits are geometrically near to each other on our processor (see Fig. 1 of the main text). b, Measured density matrix of the prepared logical Bell state, which is extracted from logical state tomography. Its fidelity is about 0.975. c, Measured density matrix in full computational space of Q₁, Q₂, Q₉₉, Q₁₀₀, with fidelity of 0.971 to the ideal density matrix. In b and c, solid bars are experimental data and hollow frames are the ideal density matrix.