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Equation 28 · Part 5 · Error Correction Is the Whole Problem in Quantum Computing

fraction

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

What this part means

Divide the expression above the line by the one below it.

Its job in the formula

The expression above the fraction bar is divided by the complete expression below it. The denominator must not be zero.

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

A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.

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Sources cited in the article section

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