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Equation 14 · Part 5 · Error Correction Is the Whole Problem in Quantum Computing

subscript

nphys=2d2−1,n_{\mathrm{phys}} = 2d^{2} - 1 ,
subscript

What this part means

The lower label selects a particular version, component, or indexed member of the quantity. For example, x₀ and xₜ can be values at different positions.

Its job in the formula

A subscript distinguishes a version, component, step, or member of a quantity. It does not automatically mean multiplication.

The passage around this formula

Distance d is the weight of the smallest undetectable logical error. A distance- d code corrects up to ⌊\lfloor (d-1)/2 ⌋\rfloor errors. For the planar surface code in its standard rotated layout, the physical cost of one logical qubit is nphys=2d2−1n_{\mathrm{phys}} = 2d^{2} - 1 . counting data and measure qubits together. A distance-7 patch therefore occupies ninety-seven physical qubits, and that is a memory holding one logical qubit, doing nothing else. It performs no gate, produces no non-Clifford operation, and reserves no routing space.

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Learn the underlying idea

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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