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Equation 28 · Part 6 · Error Correction Is the Whole Problem in Quantum Computing

addition

Λ  =  PL(d)PL(d+2).\Lambda \;=\; \frac{P_L(d)}{P_L(d+2)} .
addition

What this part means

Add the term after the plus sign to the term or group before it.

Its job in the formula

Add the term after the plus sign to the term or group before it.

The passage around this formula

so that each increase of the code distance by two multiplies the protection by a factor conventionally written Λ  =  PL(d)PL(d+2)\Lambda \;=\; \frac{P_L(d)}{P_L(d+2)} . Below threshold means Λ\Lambda > 1 . Above threshold, adding qubits makes the logical qubit worse, because each additional physical qubit contributes more error than the larger code removes. This is the sense in which qubit count is not merely an incomplete figure of merit but can be an actively misleading one.

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Learn the underlying idea

Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.

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Sources cited in the article section

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