The SWAP Gate

The SWAP gate moves a qubit's state to a neighbor - the routing Kronos's circuits need because real chips only connect adjacent qubits.

What it does

SWAP exchanges two qubits' states and is built from three CNOTs. It creates no entanglement; it relocates information.

Where it appears at Kronos

A materials Hamiltonian couples many orbitals, but hardware links only neighbors, so a compiler inserts SWAPs to bring interacting qubits together. SWAP count is a leading cost in Kronos's circuit estimates, which is why qubit routing is treated as its own optimization.

Honest note

Routing overhead is part of why fusion-scale circuits need the larger, error-corrected machines expected ~mid-2030s.