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Equation 2 · Part 1 · Error Correction Is the Whole Problem in Quantum Computing

Symbol psi

∣ψ⟩|\psi\rangle
ψ\psi

What this part means

psi is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Its job in the formula

psi is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

The passage around this formula

cannot exist for all |ψ\psi⟩\rangle , because unitarity preserves inner products and the required map does not. Wootters and Zurek established the point in 1982, in a paper whose title remains the cleanest statement of it [ 1 ] . There is no backup copy, no parity check computed by reading the data, no majority vote over three inspected replicas.

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A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the surrounding passage

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