interop

`eigenkit.chemistry.interop`

OpenFermion interop (the optional chemistry extra).

OpenFermion's FermionOperator and QubitOperator share our term structure exactly — a FermionOperator term is a tuple of (mode, action) with action 1=creation / 0=annihilation, and a QubitOperator term is a tuple of (qubit, 'X'|'Y'|'Z') — so the conversions are direct. These adapters let you (a) bring an OpenFermion-built Hamiltonian onto the spine, and (b) reach mappings OpenFermion provides (e.g. Bravyi-Kitaev) via our Observable.

The -> conversions read only the .terms mapping (no OpenFermion import needed); the to_openfermion direction imports OpenFermion lazily.

`fermion_operator_from_openfermion(operator)`

Convert an openfermion.FermionOperator to an eigenkit FermionOperator.

Parameters:

Name	Type	Description	Default
`operator`	`FermionOperator`	The fermionic operator to convert.	required

Returns:

Type	Description
`FermionOperator`	The same operator, as an eigenkit `FermionOperator`.

`observable_from_openfermion(qubit_operator, *, atol=1e-10)`

Convert an openfermion.QubitOperator to an (Observable, offset) pair.

The identity term becomes the real offset. The coefficients must be real, because the operator must be Hermitian, and a ValueError is raised otherwise.

Parameters:

Name	Type	Description	Default
`qubit_operator`	`QubitOperator`	The operator to convert.	required
`atol`	`float`	Terms whose coefficient is smaller than this value in magnitude are dropped.	`1e-10`

Returns:

Name	Type	Description
`observable`	`Observable`	The operator, without its identity term.
`offset`	`float`	The coefficient of the identity term.

`to_openfermion_fermion_operator(operator)`

Convert an eigenkit FermionOperator to an openfermion.FermionOperator.

Parameters:

Name	Type	Description	Default
`operator`	`FermionOperator`	The fermionic operator to convert.	required

Returns:

Type	Description
`FermionOperator`	The same operator, in OpenFermion.