This scan uses a determinant check to show when a two-qubit table stops looking like a product state. The uncoupled row has determinant magnitude 0, while the two CNOT input rows each reach 1/2, so the boundary is visible in the small table. Real coupling checks depend on gate calibration, state preparation, basis choice, readout assignment, finite shots, and uncertainty.
Three coupling inputs show where the product-state determinant crosses the boundary. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Uncoupled plus-plus stays product
The off row keeps four equal probabilities. Its determinant magnitude is 0.
∣det∣=0,n=0
Two CNOT inputs cross the determinant boundary
The two coupled rows use different target inputs, but both make a nonzero determinant magnitude.
rowoffzeroone∣det∣02121n011
The target-one row is a separate checked input
Changing the target input does not reuse a caption. The CNOT row is checked again from its own source state.