Grover’s search runs on three logical qubits with this new code

Quantum error correction (QEC) protects quantum information from noise by encoding logical states into a code subspace or subsystem. Beyond storage, quantum computation also requires controlled processing of encoded logical information. This is accomplished by applying transforms to logical states while preserving the code. These circuits must be fault-tolerant. Errors must not spread faster than the code’s ability to correct them, or, for purely error-detecting (distance-2) codes, at least to detect them. Code-switching offers a route to universal, fault-tolerant quantum computation by circumventing the limitation implied by the Eastin-Knill theorem against a universal transversal gate set within a single quantum code. Here, the researchers present a fault-tolerant code-switching protocol between two versions of the [[8,3,2]] code. One version supports weakly fault-tolerant single-qubit Clifford gates, while the other supports a logical CCZ gate via transversal T/T† together…