To confirm that a quantum computer has correctly encoded a specific quantum state, researchers can verify the computer’s output against a trusted reference device. This verification is especially important for quantum computers that comprise multiple modules, which must be checked against one another for consistency. However, current verification methods quickly become too costly as the number of qubits increases. Kieran Dalton of the Swiss Federal Institute of Technology (ETH) Zurich and colleagues have now demonstrated a quantum-state-verification method that should work efficiently on quantum computers comprising arbitrary numbers of qubits [1].
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