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Guided tour · Foundations · step 3 of 11

Depth is the number that costs you

Two circuits with the same gate count can take very different times to run and decohere by very different amounts.

Now go and look

Note the depth of these four parallel gates, then rewrite them all onto q[0] and compare.

Open the example

What you should see

Four gates either way. Depth 1 when they are on different qubits, depth 4 when they are stacked on one — the same gate count, four times the duration.