Qiskit / qiskit-fermions / 40703124160

98%

push

github

Refactor the fermionic circuit-level synthesis (#405)

* feat(transpiler): synthesize hop evolutions as XXPlusYYGate

The generic `PauliEvolutionGate` synthesis costs 8 CX for the image of a
fermionic hop with a complex amplitude (`XX`, `YY`, `XY`, `YX`), against
2 CX for the equivalent `XXPlusYYGate`, and a target whose only
two-qubit gate is `xx_plus_yy` cannot be reached by it at all. Qiskit
has no recognition of this multi-term form at low `optimization_level`
settings.

`HopEvolutionSynthesis` is a Qiskit `HighLevelSynthesisPlugin` for
`PauliEvolution` that recognizes a hop and emits the gate, and declines
everything else so the next method of the `HLSConfig` runs. It lives in
the qubit stage rather than in `MapperFnEvolutionSynthesis` because that
is where an upstream variant would sit, and because it then also applies
to any `PauliEvolutionGate`, not only those this package emits. The
Jordan-Wigner preset registers it ahead of the methods in a given
`hls_config` (extending a copy, never mutating the caller's), or ahead
of `"default"` if none.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* refactor(circuit): generalize the fermionic synthesis framework

Breaking an `Evolution` down in fermionic space had its own interface
(`FermionicEvolutionSynthesis`), its own attribute on the gate, and its
own pass (`FermionicTrotterization`). Other gates break down the same
way, so this lifts all three out of `Evolution` and mirrors the
fermion-to-qubit stage next to it: `F2FSynthesis`, `F2FSynthesisPlugin`,
`F2FSynthesisPluginManager` and `F2FSynthesisConfig` stand to
`F2QSynthesis*` as fermion-to-fermion stands to fermion-to-qubit.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* refactor(transpiler): decompose OrbitalRotation in fermionic space

An `OrbitalRotation` was lowered by a qubit-stage plugin that did the
Givens factorization itself and emitted `XXPlusYYGate` and `PhaseGate`
directly, which made the whole lowering vali... (continued)

356 of 362 new or added lines in 17 files covered. (98.34%)

14281 of 14540 relevant lines covered (98.22%)

449527.87 hits per line