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Equation 10 · Part 1 · Error Correction Is the Whole Problem in Quantum Computing

Symbol S_i

SiS_i
SiS_i

What this part means

SiS_i 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

SiS_i 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

An [[n, k, d]] code encodes k logical qubits into n physical qubits with distance d . The stabiliser generators are measured repeatedly. Because each SiS_i commutes with every other and with the logical operators, measuring them extracts no information about which encoded state is present. What it extracts is whether an error has anticommuted with a given check — a single classical bit per generator, per round. That bit string is the syndrome.

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A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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