MergeOrbitalRotations

class MergeOrbitalRotations

Bases: GenericPass[DAGCircuit, DAGCircuit]

A transpilation pass merging runs of consecutive orbital rotations into a single one.

Two OrbitalRotation gates applied back-to-back on the same modes compose into a single orbital rotation whose rotation_unitary is the matrix product of the two. This pass detects maximal runs of such consecutive rotations in a FermionicDAGCircuit and rewrites each into one OrbitalRotation, so the synthesis stage lowers a single (still square) decomposition instead of one per gate in the run.

A “run” is a maximal chain of OrbitalRotation nodes acting on the same mode set with nothing else intervening on those wires. Following the OrbitalRotation convention $a^\dagger_i \mapsto \sum_j U_{ji} a^\dagger_j$, applying a rotation $U_1$ and then a rotation $U_2$ maps $a^\dagger_i \mapsto \sum_j (U_2 U_1)_{ji} a^\dagger_j$, so the run’s rotations are multiplied in circuit order (later rotation on the left) to form the merged rotation_unitary. Because the merged gate implements exactly that composed basis change, the rewrite leaves the simulated state vector unchanged.

Only rotations on the identical mode set are merged: two rotations on different (even overlapping) mode sets, or rotations separated by any other operation on a shared wire, break the run and are left untouched. This is the shape produced, e.g., by two adjacent per-spin rotations on the same spin half, or by consecutive UCJ layers whose trailing and leading orbital rotations meet on the same modes.

Methods

run

Inherited Methods

execute

name

update_status