# Qiskit Fermions

> Qiskit Fermions extends Qiskit with tools for working with fermionic systems: operator data structures, a framework and library for converting operators between representations and to qubit operators (for example Jordan-Wigner and ternary-tree encodings), and a framework and library for synthesizing fermionic quantum circuits. The core is written in Rust and exposed through first-party Python and C APIs.


2026, Qiskit addons team

## Pages in this subsection

- [OperatorTrait](qiskit_fermions.operators.OperatorTrait.html.md): A protocol indicating all methods implemented by operator classes.
- [FermionAction](qiskit_fermions.operators.fermion_action.FermionAction.html.md): A fermionic creation or annihilation action.
- [FermionOperator](qiskit_fermions.operators.FermionOperator.html.md): A spin-less fermionic operator.
- [cre](qiskit_fermions.operators.cre.html.md): Constructs a creation action on the fermionic mode at `mode`.
- [ann](qiskit_fermions.operators.ann.html.md): Constructs an annihilation action on the fermionic mode at `mode`.
- [MajoranaAction](qiskit_fermions.operators.majorana_action.MajoranaAction.html.md): The MajoranaAction type. See `gamma()` for more details.
- [MajoranaOperator](qiskit_fermions.operators.MajoranaOperator.html.md): A Majorana fermion operator.
- [gamma](qiskit_fermions.operators.gamma.html.md): Create a majorana fermion.
- [EdgeAction](qiskit_fermions.operators.edge_action.EdgeAction.html.md): The EdgeAction type.
- [TransferAction](qiskit_fermions.operators.transfer_action.TransferAction.html.md): The TransferAction type.
- [EdgeVertexOperator](qiskit_fermions.operators.EdgeVertexOperator.html.md): An edge-vertex operator.
- [TransferVertexOperator](qiskit_fermions.operators.TransferVertexOperator.html.md): A transfer-vertex operator.
- [commutator](qiskit_fermions.operators.library.commutator.html.md): Computes the commutator of two operators.
- [anti_commutator](qiskit_fermions.operators.library.anti_commutator.html.md): Computes the anti-commutator of two operators.
- [double_commutator](qiskit_fermions.operators.library.double_commutator.html.md): Computes the double-commutator of three operators.
- [FCIDump](qiskit_fermions.operators.library.FCIDump.html.md): An electronic structure Hamiltonian in FCIDump format.
- [group_terms_by_electronic_structure](qiskit_fermions.operators.terms.group_terms_by_electronic_structure.html.md): Groups the terms of an operator by their electronic structure.
- [group_coeff_means](qiskit_fermions.operators.terms.group_coeff_means.html.md): Returns the mean absolute coefficient magnitude of each group.
- [groups_are_hermitian](qiskit_fermions.operators.terms.groups_are_hermitian.html.md): Returns, for each group, whether the operator formed by that group’s terms is Hermitian.
- [groups_have_uniform_coeffs](qiskit_fermions.operators.terms.groups_have_uniform_coeffs.html.md): Returns, for each group, whether all of its coefficients are numerically equal.
- [filter_diagonal_terms](qiskit_fermions.operators.terms.filter_diagonal_terms.html.md): Filters out the terms of an operator that are diagonal in the occupation-number basis.
- [canonical_order](qiskit_fermions.operators.terms.canonical_order.html.md): Returns a copy of an operator with its terms sorted into a canonical order.
- [group_order](qiskit_fermions.operators.terms.group_order.html.md): Returns a copy of an operator with its terms ordered by group index.
- [order_terms](qiskit_fermions.operators.terms.order_terms.html.md): Returns a copy of an operator with its terms reordered by a user-provided key.
- [map_fermion_action_generators](qiskit_fermions.mappers.map_fermion_action_generators.html.md): Map a `FermionOperator` to another operator type.
- [map_majorana_action_generators](qiskit_fermions.mappers.map_majorana_action_generators.html.md): Map a `MajoranaOperator` to another operator type.
- [map_edge_vertex_generators](qiskit_fermions.mappers.map_edge_vertex_generators.html.md): Map a `EdgeVertexOperator` to another operator type.
- [map_transfer_vertex_generators](qiskit_fermions.mappers.map_transfer_vertex_generators.html.md): Map a `TransferVertexOperator` to another operator type.
- [TernaryTree](qiskit_fermions.mappers.TernaryTree.html.md): A ternary tree defining a fermion-to-qubit encoding.
- [TernaryTreeEncoding](qiskit_fermions.mappers.TernaryTreeEncoding.html.md): A ternary tree compiled into the Pauli images of its Majorana operators.
- [fermion_operator](qiskit_fermions.mappers.library.fermion_operator.html.md): Converts an operator into a `FermionOperator`.
- [jordan_wigner](qiskit_fermions.mappers.library.jordan_wigner.html.md): Map an operator to a `SparseObservable` under the Jordan-Wigner transformation.
- [majorana_operator](qiskit_fermions.mappers.library.majorana_operator.html.md): Converts an operator into a `MajoranaOperator`.
- [ternary_tree](qiskit_fermions.mappers.library.ternary_tree.html.md): Map an operator to a `SparseObservable` under a ternary-tree encoding.
- [fermion_jordan_wigner](qiskit_fermions.mappers.library.fermion_jordan_wigner.html.md): Map a `FermionOperator` to a `SparseObservable` under the
- [majorana_jordan_wigner](qiskit_fermions.mappers.library.majorana_jordan_wigner.html.md): Map a `MajoranaOperator` to a `SparseObservable` under the
- [edge_vertex_jordan_wigner](qiskit_fermions.mappers.library.edge_vertex_jordan_wigner.html.md): Map an `EdgeVertexOperator` to a `SparseObservable` under the
- [transfer_vertex_jordan_wigner](qiskit_fermions.mappers.library.transfer_vertex_jordan_wigner.html.md): Map a `TransferVertexOperator` to a `SparseObservable` under
- [fermion_to_majorana](qiskit_fermions.mappers.library.fermion_to_majorana.html.md): Map a `FermionOperator` to a `MajoranaOperator`.
- [majorana_to_fermion](qiskit_fermions.mappers.library.majorana_to_fermion.html.md): Map a `MajoranaOperator` to a `FermionOperator`.
- [edge_vertex_to_fermion](qiskit_fermions.mappers.library.edge_vertex_to_fermion.html.md): Map an `EdgeVertexOperator` to a `FermionOperator`.
- [edge_vertex_to_majorana](qiskit_fermions.mappers.library.edge_vertex_to_majorana.html.md): Map an `EdgeVertexOperator` to a `MajoranaOperator`.
- [transfer_vertex_to_fermion](qiskit_fermions.mappers.library.transfer_vertex_to_fermion.html.md): Map a `TransferVertexOperator` to a `FermionOperator`.
- [transfer_vertex_to_majorana](qiskit_fermions.mappers.library.transfer_vertex_to_majorana.html.md): Map a `TransferVertexOperator` to a `MajoranaOperator`.
- [transfer_vertex_to_edge_vertex](qiskit_fermions.mappers.library.transfer_vertex_to_edge_vertex.html.md): Map a `TransferVertexOperator` to an `EdgeVertexOperator`.
- [fermion_ternary_tree](qiskit_fermions.mappers.library.fermion_ternary_tree.html.md): Map a `FermionOperator` to a `SparseObservable` under a
- [majorana_ternary_tree](qiskit_fermions.mappers.library.majorana_ternary_tree.html.md): Map a `MajoranaOperator` to a `SparseObservable` under a
- [edge_vertex_ternary_tree](qiskit_fermions.mappers.library.edge_vertex_ternary_tree.html.md): Map an `EdgeVertexOperator` to a `SparseObservable` under a
- [transfer_vertex_ternary_tree](qiskit_fermions.mappers.library.transfer_vertex_ternary_tree.html.md): Map a `TransferVertexOperator` to a `SparseObservable` under
- [build_excitation_span_minimization_model](qiskit_fermions.mappers.optimization.build_excitation_span_minimization_model.html.md): Build a Pyomo model for ordering fermionic modes to minimize excitation spans.
- [FermionicDAGCircuit](qiskit_fermions.circuit.FermionicDAGCircuit.html.md): A type alias of `DAGCircuit`.
- [FermionicMode](qiskit_fermions.circuit.FermionicMode.html.md): A type alias of `Qubit`.
- [FermionicRegister](qiskit_fermions.circuit.FermionicRegister.html.md): A type alias of `QubitRegister`.
- [FermionicSpecifier](qiskit_fermions.circuit.FermionicSpecifier.html.md): A type alias equivalent to Qiskit’s `QubitSpecifier` but for fermionic modes.
- [FermionicCircuit](qiskit_fermions.circuit.FermionicCircuit.html.md): A wrapper around `QuantumCircuit` for expressing fermionic circuits.
- [FermionicInstruction](qiskit_fermions.circuit.FermionicInstruction.html.md): The base class for all instructions acting on fermionic modes.
- [FermionicGate](qiskit_fermions.circuit.FermionicGate.html.md): The base class for all fermionic gates.
- [Evolution](qiskit_fermions.circuit.library.Evolution.html.md): Implements the time evolution of an operator.
- [InitializeModes](qiskit_fermions.circuit.library.InitializeModes.html.md): Prepares (or, under simulation, certifies) a fermionic mode occupation.
- [OrbitalRotation](qiskit_fermions.circuit.library.OrbitalRotation.html.md): Implements an orbital rotation.
- [PrepareSlaterDeterminant](qiskit_fermions.circuit.library.PrepareSlaterDeterminant.html.md): Prepares a Slater determinant from an occupation and an orbital rotation.
- [UCC](qiskit_fermions.circuit.library.UCC.html.md): Implements the unitary coupled-cluster singles and doubles (UCCSD) ansatz.
- [UCJ](qiskit_fermions.circuit.library.UCJ.html.md): Implements the (local) unitary cluster Jastrow ((L)UCJ) ansatz.
- [FermionicMeasure](qiskit_fermions.circuit.library.FermionicMeasure.html.md): A measurement of a single fermionic mode, writing its outcome into one classical bit.
- [FermionicEvolutionSynthesis](qiskit_fermions.circuit.library.synthesis.FermionicEvolutionSynthesis.html.md): The interface for fermion-to-fermion synthesis of an `Evolution` gate.
- [FermionicLieTrotter](qiskit_fermions.circuit.library.synthesis.FermionicLieTrotter.html.md): The first-order Lie-Trotter product formula, applied in fermionic space.
- [FermionicSuzukiTrotter](qiskit_fermions.circuit.library.synthesis.FermionicSuzukiTrotter.html.md): The higher-order Suzuki-Trotter product formula, applied in fermionic space.
- [F2QLayout](qiskit_fermions.transpiler.F2QLayout.html.md): A mapping of fermionic mode registers to quantum registers.
- [FermionicPassManager](qiskit_fermions.transpiler.FermionicPassManager.html.md): A transpiler pass manager converting one `FermionicCircuit` to another.
- [FermionicCircuitToDAG](qiskit_fermions.transpiler.FermionicCircuitToDAG.html.md): Converts a `FermionicCircuit` to a `FermionicDAGCircuit`.
- [FermionicDAGToCircuit](qiskit_fermions.transpiler.FermionicDAGToCircuit.html.md): Converts a `FermionicDAGCircuit` to a `FermionicCircuit`.
- [QuantumDAGToCircuit](qiskit_fermions.transpiler.QuantumDAGToCircuit.html.md): Converts a `DAGCircuit` to a `QuantumCircuit`.
- [FermionicTrotterization](qiskit_fermions.transpiler.passes.FermionicTrotterization.html.md): A transpilation pass Trotterizing `Evolution` gates in fermionic space.
- [MergeOrbitalRotations](qiskit_fermions.transpiler.passes.MergeOrbitalRotations.html.md): A transpilation pass merging runs of consecutive orbital rotations into a single one.
- [MergeSlaterDeterminantPreparation](qiskit_fermions.transpiler.passes.MergeSlaterDeterminantPreparation.html.md): A transpilation pass fusing an initialization and rotation into a Slater determinant prep.
- [QDriftTrotterization](qiskit_fermions.transpiler.passes.QDriftTrotterization.html.md): A transpilation pass to Trotterize `Evolution` gates via the qDRIFT protocol.
- [RelabelModes](qiskit_fermions.transpiler.passes.RelabelModes.html.md): A transpilation pass to relabel the fermionic modes.
- [TrivialF2QLayout](qiskit_fermions.transpiler.passes.TrivialF2QLayout.html.md): Trivially maps $n$ fermionic modes to $n$ qubits.
- [CustomF2QLayout](qiskit_fermions.transpiler.passes.CustomF2QLayout.html.md): Sets the user-provided `F2QLayout` in the transpiler.
- [F2QSynthesis](qiskit_fermions.transpiler.passes.F2QSynthesis.html.md): A transpilation pass to map fermion-based circuit instructions to qubit-based ones.
- [F2QSynthesisConfig](qiskit_fermions.transpiler.passes.synthesis.synthesis.F2QSynthesisConfig.html.md): The dictionary type used to configure the `F2QSynthesis.methods`.
- [F2QSynthesisPlugin](qiskit_fermions.transpiler.passes.synthesis.F2QSynthesisPlugin.html.md): The protocol for plugins to the `F2QSynthesis` transpiler pass.
- [F2QSynthesisPluginManager](qiskit_fermions.transpiler.passes.synthesis.F2QSynthesisPluginManager.html.md): A simple manager of the installed fermion-to-qubit synthesis plugins.
- [GivensDecompositionOrbitalRotationSynthesis](qiskit_fermions.transpiler.passes.synthesis.GivensDecompositionOrbitalRotationSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `OrbitalRotation` into Givens rotations.
- [GivensDecompositionSlaterDeterminantSynthesis](qiskit_fermions.transpiler.passes.synthesis.GivensDecompositionSlaterDeterminantSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `PrepareSlaterDeterminant`.
- [MapperFnEvolutionSynthesis](qiskit_fermions.transpiler.passes.synthesis.MapperFnEvolutionSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `Evolution` under a custom mapping.
- [TrivialOccupationFermionicMeasureSynthesis](qiskit_fermions.transpiler.passes.synthesis.TrivialOccupationFermionicMeasureSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `FermionicMeasure` with trivial occupation.
- [TrivialOccupationInitializeModesSynthesis](qiskit_fermions.transpiler.passes.synthesis.TrivialOccupationInitializeModesSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `InitializeModes` with trivial occupation.
- [group_wise](qiskit_fermions.transpiler.passes.synthesis.group_wise.html.md): Wraps a mapper function so that it maps an operator one group at a time.
- [simplify](qiskit_fermions.transpiler.passes.synthesis.simplify.html.md): Wraps a mapper function so that it simplifies the operator it returns.
- [map_node_single_register](qiskit_fermions.transpiler.passes.utils.map_node_single_register.html.md): Map the single fermionic mode register acted upon by the circuit operation.
- [generate_preset_jw_pass_manager](qiskit_fermions.transpiler.presets.generate_preset_jw_pass_manager.html.md): Generates a preset transpiler pipeline based on the `jordan_wigner()` mapping.
- [givens_decomposition](qiskit_fermions.linalg.givens_decomposition.html.md): Decomposes a unitary matrix into Givens rotations and diagonal phases.
- [givens_decomposition_slater](qiskit_fermions.linalg.givens_decomposition_slater.html.md): Decomposes the occupied orbitals of a Slater determinant into Givens rotations.
- [SupportsApplyUnitaryPlaced](qiskit_fermions.protocols.SupportsApplyUnitaryPlaced.html.md): A package-specific extension of `ffsim.SupportsApplyUnitary`.
- [SupportsCommutators](qiskit_fermions.protocols.SupportsCommutators.html.md): A Protocol indicating support for efficient commutator generation.
- [SupportsFermionOperator](qiskit_fermions.protocols.SupportsFermionOperator.html.md): This package’s operator-conversion contract, converting an operator to a `FermionOperator`.
- [SupportsMajoranaOperator](qiskit_fermions.protocols.SupportsMajoranaOperator.html.md): An equivalent of the `SupportsFermionOperator` protocol, targeting Majorana operators.

## Optional

- [Top-level llms.txt](../llms.txt): Complete documentation index.