The Toffoli Gate

The Toffoli gate brings classical AND into a reversible quantum circuit - the arithmetic Kronos needs inside energy-estimation routines.

What it does

Toffoli (CCNOT) flips a target only when two controls are both |1>, computing a AND b reversibly. It is non-Clifford, costing several T gates.

Where it appears at Kronos

Phase-estimation and arithmetic sub-circuits used to extract material energies rely on reversible adders and comparators built from Toffoli gates, so its cost feeds straight into Kronos's feasibility estimates.

Honest note

Toffoli-heavy circuits are a fault-tolerant expense realized ~mid-2030s.