Concept

Pauli Propagation

Pauli propagation is a technique for classically simulating the evolution of a quantum system by following how Pauli operators—simple single‑qubit observables that form a convenient basis for describing quantum states—are transformed as they pass through each gate in a circuit. Rather than tracking the full state vector, which grows exponentially with the number of qubits, the method works in the Heisenberg picture and records the algebraic changes to these operators step by step. By the end of the circuit one obtains an explicit expression for any observable of interest as a product of Pauli strings, allowing its expectation value to be evaluated efficiently on a classical computer.

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Stop Fixing Quantum Errors. Ask the Right Question Instead.
"You can take those inverses and push them backward through the ideal circuit on a classical computer — a technique called Pauli propagation — folding them into the observable itself."