# 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

- [Qiskit Fermions](index.html.md): Overview of Qiskit Fermions, an extension of the Qiskit SDK for fermionic systems: operator data structures, operator conversion methods including fermion-to-qubit encodings, fermionic circuits, and a transpilation pipeline with fermion-to-fermion and fermion-to-qubit stages that turns them into qubit circuits.
- [Installation instructions](install.html.md): Choose between the installation instructions for the Python API and the C API of Qiskit Fermions.
- [Install the C API](install-c.html.md): Build the Qiskit Fermions C API from source: install the Rust toolchain and clang, compile the Qiskit C API and then the qiskit-fermions C API, and optionally run the C unit tests.
- [Install the Python API](install-py.html.md): Install the Qiskit Fermions Python package from PyPI with pip, or from source for development, including the optional dependencies and how to verify and test the installation.
- [Overview](guides/overview.html.md): Overview of the Qiskit Fermions guides, grouped by topic, with links to each one.
- [Simulate 1D Fermi-Hubbard dynamics with flow sets](guides/1d_fermi_hubbard.html.md): Tutorial that builds a circuit of constant two-qubit depth for the time dynamics of the spinless one-dimensional Fermi-Hubbard model: group terms into flow sets before mapping, write a custom ancilla-based encoding, and synthesize with the flow sets.
- [Simulate 2D Fermi-Hubbard dynamics with flow sets](guides/2d_fermi_hubbard.html.md): Tutorial that extends the flow-set approach to the spinless two-dimensional Fermi-Hubbard model on a square lattice with the Verstraete-Cirac encoding, then verifies the circuit, the physics on the stabilizer subspace, and Trotter convergence.
- [More guides](guides/index.html.md): Table of contents of all Qiskit Fermions guides.
- [Design principles of operator representations](guides/operators.html.md): Design principles shared by all operator representations in qiskit_fermions.operators, such as sparse term storage, mode-based indexing, term grouping, and arithmetic.
- [Group operator terms: use the operator structure](guides/grouping.html.md): How to define and analyze a grouping of operator terms through the groups array of an operator, and why grouping matters for circuit synthesis.
- [Map operator representations](guides/mappers.html.md): How to implement a custom operator mapper, use the library mappers, and choose a fermion-to-qubit encoding with ternary trees.
- [Work with fermionic circuits](guides/circuit.html.md): How to build, repeat, measure, and transpile a FermionicCircuit, which implements quantum algorithms in fermionic space instead of mapping to qubits first.
- [Generate SqDRIFT circuits](guides/sqdrift.html.md): Getting-started guide that generates an ensemble of randomized qDRIFT time-evolution circuits for sample-based quantum diagonalization (SqDRIFT) from an electronic structure Hamiltonian, from term grouping to transpilation.
- [Generate Krylov time-evolution circuits (SKQD)](guides/skqd.html.md): Getting-started guide that builds the Krylov time-evolution circuits of sample-based Krylov quantum diagonalization (SKQD) for the single-impurity Anderson model, transpiles them, and diagonalizes in the sampled subspace.
- [Transpile fermionic circuits](guides/transpilation.html.md): How to transpile a FermionicCircuit to a qubit QuantumCircuit through the stages of the fermionic transpiler pipeline, with a worked Jordan-Wigner example.
- [Synthesize an Evolution gate in fermionic space](guides/fermionic_synthesis.html.md): How to synthesize an Evolution gate into smaller fermionic gates with product formulas, on one gate or across a whole pipeline, and how to measure the payoff.
- [Optimize Slater determinant preparation](guides/merge_slater_determinant.html.md): How the MergeSlaterDeterminantPreparation transpiler pass rewrites an InitializeModes gate followed by an OrbitalRotation gate into a PrepareSlaterDeterminant gate, which unlocks a cheaper synthesis.
- [Transpile an LUCJ ansatz](guides/lucj.html.md): How to transpile a local unitary cluster Jastrow (LUCJ) ansatz built with ffsim: turn it into a fermionic circuit, lower it onto qubits through the fermion-to-qubit encoding of your choice, and match the device topology.
- [How this package relates to ffsim](guides/ffsim.html.md): How Qiskit Fermions and ffsim divide the work: ffsim owns the ansatz operators and fast fixed-particle-number simulation, while Qiskit Fermions owns fermionic circuits and their transpilation under any encoding.
- [`qiskit-fermions` Python API reference](pydoc/index.html.md): Reference for the Python API of qiskit-fermions, covering operators, mappers, circuits, the transpiler, linear algebra, protocols, and utilities.
- [Operator Representations](pydoc/qiskit_fermions.operators.html.md): Data structures for representing fermionic operators in different bases: the second-quantization FermionOperator, the MajoranaOperator, and the EdgeVertexOperator and TransferVertexOperator interaction operators.
- [OperatorTrait](stubs/qiskit_fermions.operators.OperatorTrait.html.md): A protocol indicating all methods implemented by operator classes.
- [FermionAction](stubs/qiskit_fermions.operators.fermion_action.FermionAction.html.md): A fermionic creation or annihilation action.
- [FermionOperator](stubs/qiskit_fermions.operators.FermionOperator.html.md): A spin-less fermionic operator.
- [cre](stubs/qiskit_fermions.operators.cre.html.md): Constructs a creation action on the fermionic mode at `mode`.
- [ann](stubs/qiskit_fermions.operators.ann.html.md): Constructs an annihilation action on the fermionic mode at `mode`.
- [MajoranaAction](stubs/qiskit_fermions.operators.majorana_action.MajoranaAction.html.md): The MajoranaAction type. See `gamma()` for more details.
- [MajoranaOperator](stubs/qiskit_fermions.operators.MajoranaOperator.html.md): A Majorana fermion operator.
- [gamma](stubs/qiskit_fermions.operators.gamma.html.md): Create a majorana fermion.
- [EdgeAction](stubs/qiskit_fermions.operators.edge_action.EdgeAction.html.md): The EdgeAction type.
- [TransferAction](stubs/qiskit_fermions.operators.transfer_action.TransferAction.html.md): The TransferAction type.
- [EdgeVertexOperator](stubs/qiskit_fermions.operators.EdgeVertexOperator.html.md): An edge-vertex operator.
- [TransferVertexOperator](stubs/qiskit_fermions.operators.TransferVertexOperator.html.md): A transfer-vertex operator.
- [Operator Library](pydoc/qiskit_fermions.operators.library.html.md): Tools to construct commonly used operators, such as commutators of operators and electronic structure Hamiltonians from FCIDump files.
- [commutator](stubs/qiskit_fermions.operators.library.commutator.html.md): Computes the commutator of two operators.
- [anti_commutator](stubs/qiskit_fermions.operators.library.anti_commutator.html.md): Computes the anti-commutator of two operators.
- [double_commutator](stubs/qiskit_fermions.operators.library.double_commutator.html.md): Computes the double-commutator of three operators.
- [FCIDump](stubs/qiskit_fermions.operators.library.FCIDump.html.md): An electronic structure Hamiltonian in FCIDump format.
- [Operator Terms](pydoc/qiskit_fermions.operators.terms.html.md): Routines that operate on the individual terms of an operator, to group, filter, and order them.
- [group_terms_by_electronic_structure](stubs/qiskit_fermions.operators.terms.group_terms_by_electronic_structure.html.md): Groups the terms of an operator by their electronic structure.
- [group_coeff_means](stubs/qiskit_fermions.operators.terms.group_coeff_means.html.md): Returns the mean absolute coefficient magnitude of each group.
- [groups_are_hermitian](stubs/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](stubs/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](stubs/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](stubs/qiskit_fermions.operators.terms.canonical_order.html.md): Returns a copy of an operator with its terms sorted into a canonical order.
- [group_order](stubs/qiskit_fermions.operators.terms.group_order.html.md): Returns a copy of an operator with its terms ordered by group index.
- [order_terms](stubs/qiskit_fermions.operators.terms.order_terms.html.md): Returns a copy of an operator with its terms reordered by a user-provided key.
- [Representation Mappers](pydoc/qiskit_fermions.mappers.html.md): Framework for implementing custom operator representation mappers, plus the ternary-tree data structures behind tree-based fermion-to-qubit encodings.
- [map_fermion_action_generators](stubs/qiskit_fermions.mappers.map_fermion_action_generators.html.md): Map a `FermionOperator` to another operator type.
- [map_majorana_action_generators](stubs/qiskit_fermions.mappers.map_majorana_action_generators.html.md): Map a `MajoranaOperator` to another operator type.
- [map_edge_vertex_generators](stubs/qiskit_fermions.mappers.map_edge_vertex_generators.html.md): Map a `EdgeVertexOperator` to another operator type.
- [map_transfer_vertex_generators](stubs/qiskit_fermions.mappers.map_transfer_vertex_generators.html.md): Map a `TransferVertexOperator` to another operator type.
- [TernaryTree](stubs/qiskit_fermions.mappers.TernaryTree.html.md): A ternary tree defining a fermion-to-qubit encoding.
- [TernaryTreeEncoding](stubs/qiskit_fermions.mappers.TernaryTreeEncoding.html.md): A ternary tree compiled into the Pauli images of its Majorana operators.
- [Mapper Library](pydoc/qiskit_fermions.mappers.library.html.md): Implementations of common operator mappers, such as the Jordan-Wigner and ternary-tree mappings to qubit operators, and conversions between operator representations.
- [fermion_operator](stubs/qiskit_fermions.mappers.library.fermion_operator.html.md): Converts an operator into a `FermionOperator`.
- [jordan_wigner](stubs/qiskit_fermions.mappers.library.jordan_wigner.html.md): Map an operator to a `SparseObservable` under the Jordan-Wigner transformation.
- [majorana_operator](stubs/qiskit_fermions.mappers.library.majorana_operator.html.md): Converts an operator into a `MajoranaOperator`.
- [ternary_tree](stubs/qiskit_fermions.mappers.library.ternary_tree.html.md): Map an operator to a `SparseObservable` under a ternary-tree encoding.
- [fermion_jordan_wigner](stubs/qiskit_fermions.mappers.library.fermion_jordan_wigner.html.md): Map a `FermionOperator` to a `SparseObservable` under the
- [majorana_jordan_wigner](stubs/qiskit_fermions.mappers.library.majorana_jordan_wigner.html.md): Map a `MajoranaOperator` to a `SparseObservable` under the
- [edge_vertex_jordan_wigner](stubs/qiskit_fermions.mappers.library.edge_vertex_jordan_wigner.html.md): Map an `EdgeVertexOperator` to a `SparseObservable` under the
- [transfer_vertex_jordan_wigner](stubs/qiskit_fermions.mappers.library.transfer_vertex_jordan_wigner.html.md): Map a `TransferVertexOperator` to a `SparseObservable` under
- [fermion_to_majorana](stubs/qiskit_fermions.mappers.library.fermion_to_majorana.html.md): Map a `FermionOperator` to a `MajoranaOperator`.
- [majorana_to_fermion](stubs/qiskit_fermions.mappers.library.majorana_to_fermion.html.md): Map a `MajoranaOperator` to a `FermionOperator`.
- [edge_vertex_to_fermion](stubs/qiskit_fermions.mappers.library.edge_vertex_to_fermion.html.md): Map an `EdgeVertexOperator` to a `FermionOperator`.
- [edge_vertex_to_majorana](stubs/qiskit_fermions.mappers.library.edge_vertex_to_majorana.html.md): Map an `EdgeVertexOperator` to a `MajoranaOperator`.
- [transfer_vertex_to_fermion](stubs/qiskit_fermions.mappers.library.transfer_vertex_to_fermion.html.md): Map a `TransferVertexOperator` to a `FermionOperator`.
- [transfer_vertex_to_majorana](stubs/qiskit_fermions.mappers.library.transfer_vertex_to_majorana.html.md): Map a `TransferVertexOperator` to a `MajoranaOperator`.
- [transfer_vertex_to_edge_vertex](stubs/qiskit_fermions.mappers.library.transfer_vertex_to_edge_vertex.html.md): Map a `TransferVertexOperator` to an `EdgeVertexOperator`.
- [fermion_ternary_tree](stubs/qiskit_fermions.mappers.library.fermion_ternary_tree.html.md): Map a `FermionOperator` to a `SparseObservable` under a
- [majorana_ternary_tree](stubs/qiskit_fermions.mappers.library.majorana_ternary_tree.html.md): Map a `MajoranaOperator` to a `SparseObservable` under a
- [edge_vertex_ternary_tree](stubs/qiskit_fermions.mappers.library.edge_vertex_ternary_tree.html.md): Map an `EdgeVertexOperator` to a `SparseObservable` under a
- [transfer_vertex_ternary_tree](stubs/qiskit_fermions.mappers.library.transfer_vertex_ternary_tree.html.md): Map a `TransferVertexOperator` to a `SparseObservable` under
- [Mapper Optimizations](pydoc/qiskit_fermions.mappers.optimization.html.md): This module provides various routines for optimizing fermion-to-qubit mappings.
- [build_excitation_span_minimization_model](stubs/qiskit_fermions.mappers.optimization.build_excitation_span_minimization_model.html.md): Build a Pyomo model for ordering fermionic modes to minimize excitation spans.
- [Circuit Representation](pydoc/qiskit_fermions.circuit.html.md): Fermionic circuits: FermionicCircuit and related types that interpret Qiskit circuits as acting on fermionic modes rather than qubits.
- [FermionicDAGCircuit](stubs/qiskit_fermions.circuit.FermionicDAGCircuit.html.md): A type alias of `DAGCircuit`.
- [FermionicMode](stubs/qiskit_fermions.circuit.FermionicMode.html.md): A type alias of `Qubit`.
- [FermionicRegister](stubs/qiskit_fermions.circuit.FermionicRegister.html.md): A type alias of `QubitRegister`.
- [FermionicSpecifier](stubs/qiskit_fermions.circuit.FermionicSpecifier.html.md): A type alias equivalent to Qiskit’s `QubitSpecifier` but for fermionic modes.
- [FermionicCircuit](stubs/qiskit_fermions.circuit.FermionicCircuit.html.md): A wrapper around `QuantumCircuit` for expressing fermionic circuits.
- [FermionicInstruction](stubs/qiskit_fermions.circuit.FermionicInstruction.html.md): The base class for all instructions acting on fermionic modes.
- [FermionicGate](stubs/qiskit_fermions.circuit.FermionicGate.html.md): The base class for all fermionic gates.
- [Circuit Library](pydoc/qiskit_fermions.circuit.library.html.md): Library of fermionic gates and instructions, such as time evolution, mode initialization, orbital rotations, and measurement.
- [Evolution](stubs/qiskit_fermions.circuit.library.Evolution.html.md): Implements the time evolution of an operator.
- [InitializeModes](stubs/qiskit_fermions.circuit.library.InitializeModes.html.md): Prepares (or, under simulation, certifies) a fermionic mode occupation.
- [OrbitalRotation](stubs/qiskit_fermions.circuit.library.OrbitalRotation.html.md): Implements an orbital rotation.
- [PrepareSlaterDeterminant](stubs/qiskit_fermions.circuit.library.PrepareSlaterDeterminant.html.md): Prepares a Slater determinant from an occupation and an orbital rotation.
- [UCC](stubs/qiskit_fermions.circuit.library.UCC.html.md): Implements the unitary coupled-cluster singles and doubles (UCCSD) ansatz.
- [UCJ](stubs/qiskit_fermions.circuit.library.UCJ.html.md): Implements the (local) unitary cluster Jastrow ((L)UCJ) ansatz.
- [FermionicMeasure](stubs/qiskit_fermions.circuit.library.FermionicMeasure.html.md): A measurement of a single fermionic mode, writing its outcome into one classical bit.
- [Circuit Library Synthesis (`F2F`)](pydoc/qiskit_fermions.circuit.library.synthesis.html.md): Fermion-to-fermion synthesis methods that break a gate down into smaller fermionic gates, such as Trotter and qDRIFT formulas for an Evolution gate, plus the F2FSynthesisPlugin interface for custom methods, which the F2FSynthesis transpiler pass applies.
- [F2FSynthesisPlugin](stubs/qiskit_fermions.circuit.library.synthesis.F2FSynthesisPlugin.html.md): The protocol for plugins to the `F2FSynthesis` transpiler pass.
- [F2FSynthesisPluginManager](stubs/qiskit_fermions.circuit.library.synthesis.F2FSynthesisPluginManager.html.md): A simple manager of the installed fermion-to-fermion synthesis plugins.
- [FermionicLieTrotter](stubs/qiskit_fermions.circuit.library.synthesis.FermionicLieTrotter.html.md): The first-order Lie-Trotter product formula, applied in fermionic space.
- [FermionicSuzukiTrotter](stubs/qiskit_fermions.circuit.library.synthesis.FermionicSuzukiTrotter.html.md): The higher-order Suzuki-Trotter product formula, applied in fermionic space.
- [FermionicQDrift](stubs/qiskit_fermions.circuit.library.synthesis.FermionicQDrift.html.md): A synthesis method that Trotterizes an `Evolution` via the qDRIFT protocol.
- [FermionicGivensDecomposition](stubs/qiskit_fermions.circuit.library.synthesis.FermionicGivensDecomposition.html.md): The decomposition of an orbital rotation into Givens rotations and phases.
- [FermionicSlaterGivensDecomposition](stubs/qiskit_fermions.circuit.library.synthesis.FermionicSlaterGivensDecomposition.html.md): The decomposition of a Slater determinant preparation into Givens rotations.
- [QDriftSampler](stubs/qiskit_fermions.circuit.library.synthesis.QDriftSampler.html.md): The draws of the qDRIFT protocol for one `Evolution` gate.
- [Transpiler](pydoc/qiskit_fermions.transpiler.html.md): How Qiskit Fermions transpiles a FermionicCircuit to a QuantumCircuit: the transpilation stages, the pass manager, and the layout of fermionic modes onto qubits.
- [F2QLayout](stubs/qiskit_fermions.transpiler.F2QLayout.html.md): A mapping of fermionic mode registers to quantum registers.
- [FermionicPassManager](stubs/qiskit_fermions.transpiler.FermionicPassManager.html.md): A transpiler pass manager converting one `FermionicCircuit` to another.
- [FermionicCircuitToDAG](stubs/qiskit_fermions.transpiler.FermionicCircuitToDAG.html.md): Converts a `FermionicCircuit` to a `FermionicDAGCircuit`.
- [FermionicDAGToCircuit](stubs/qiskit_fermions.transpiler.FermionicDAGToCircuit.html.md): Converts a `FermionicDAGCircuit` to a `FermionicCircuit`.
- [QuantumDAGToCircuit](stubs/qiskit_fermions.transpiler.QuantumDAGToCircuit.html.md): Converts a `DAGCircuit` to a `QuantumCircuit`.
- [Transpiler Passes](pydoc/qiskit_fermions.transpiler.passes.html.md): Transpiler passes for the stages of the fermionic transpiler pipeline, such as the fermion-to-fermion and fermion-to-qubit synthesis passes.
- [F2FSynthesis](stubs/qiskit_fermions.transpiler.passes.F2FSynthesis.html.md): A transpilation pass breaking gates down into smaller ones in fermionic space.
- [F2FSynthesisConfig](stubs/qiskit_fermions.transpiler.passes.optimization.f2f_synthesis.F2FSynthesisConfig.html.md): The dictionary type used to configure the `F2FSynthesis.methods`.
- [MergeEvolutions](stubs/qiskit_fermions.transpiler.passes.MergeEvolutions.html.md): A transpilation pass merging consecutive `Evolution` gates of the same operator.
- [MergeOrbitalRotations](stubs/qiskit_fermions.transpiler.passes.MergeOrbitalRotations.html.md): A transpilation pass merging runs of consecutive orbital rotations into a single one.
- [MergeSlaterDeterminantPreparation](stubs/qiskit_fermions.transpiler.passes.MergeSlaterDeterminantPreparation.html.md): A transpilation pass fusing an initialization and rotation into a Slater determinant prep.
- [QDriftTrotterization](stubs/qiskit_fermions.transpiler.passes.QDriftTrotterization.html.md): A transpilation pass to Trotterize `Evolution` gates via qDRIFT, skipping trivial draws.
- [RelabelModes](stubs/qiskit_fermions.transpiler.passes.RelabelModes.html.md): A transpilation pass to relabel the fermionic modes.
- [FermionicTrotterization](stubs/qiskit_fermions.transpiler.passes.FermionicTrotterization.html.md): **DEPRECATED** The former pass to Trotterize `Evolution` gates.
- [TrivialF2QLayout](stubs/qiskit_fermions.transpiler.passes.TrivialF2QLayout.html.md): Trivially maps $n$ fermionic modes to $n$ qubits.
- [CustomF2QLayout](stubs/qiskit_fermions.transpiler.passes.CustomF2QLayout.html.md): Sets the user-provided `F2QLayout` in the transpiler.
- [F2QSynthesis](stubs/qiskit_fermions.transpiler.passes.F2QSynthesis.html.md): A transpilation pass to map fermion-based circuit instructions to qubit-based ones.
- [F2QSynthesisConfig](stubs/qiskit_fermions.transpiler.passes.synthesis.f2q_synthesis.F2QSynthesisConfig.html.md): The dictionary type used to configure the `F2QSynthesis.methods`.
- [Transpiler Pass Synthesis (`F2Q`)](pydoc/qiskit_fermions.transpiler.passes.synthesis.html.md): Plugin interface of the F2QSynthesis transpiler pass, which maps fermionic instructions to qubit instructions, and the plugins that implement it.
- [F2QSynthesisPlugin](stubs/qiskit_fermions.transpiler.passes.synthesis.F2QSynthesisPlugin.html.md): The protocol for plugins to the `F2QSynthesis` transpiler pass.
- [F2QSynthesisPluginManager](stubs/qiskit_fermions.transpiler.passes.synthesis.F2QSynthesisPluginManager.html.md): A simple manager of the installed fermion-to-qubit synthesis plugins.
- [MapperFnEvolutionSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.MapperFnEvolutionSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `Evolution` under a custom mapping.
- [TrivialOccupationFermionicMeasureSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.TrivialOccupationFermionicMeasureSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `FermionicMeasure` with trivial occupation.
- [TrivialOccupationInitializeModesSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.TrivialOccupationInitializeModesSynthesis.html.md): A `F2QSynthesisPlugin` for transpiling `InitializeModes` with trivial occupation.
- [GivensDecompositionOrbitalRotationSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.GivensDecompositionOrbitalRotationSynthesis.html.md): **DEPRECATED** The former plugin for transpiling an `OrbitalRotation` into Givens rotations.
- [GivensDecompositionSlaterDeterminantSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.GivensDecompositionSlaterDeterminantSynthesis.html.md): **DEPRECATED** The former plugin for transpiling a `PrepareSlaterDeterminant` into Givens rotations.
- [HopEvolutionSynthesis](stubs/qiskit_fermions.transpiler.passes.synthesis.HopEvolutionSynthesis.html.md): A high-level synthesis plugin for the evolution under a hop between two qubits.
- [group_wise](stubs/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](stubs/qiskit_fermions.transpiler.passes.synthesis.simplify.html.md): Wraps a mapper function so that it simplifies the operator it returns.
- [Transpiler Pass Utilities](pydoc/qiskit_fermions.transpiler.passes.utils.html.md): Several convenience functions are provided to simplify the implementation of common operations
- [map_node_single_register](stubs/qiskit_fermions.transpiler.passes.utils.map_node_single_register.html.md): Map the single fermionic mode register acted upon by the circuit operation.
- [Transpiler Presets](pydoc/qiskit_fermions.transpiler.presets.html.md): Functions that generate predefined transpiler pipelines, such as one for the Jordan-Wigner encoding.
- [generate_preset_jw_pass_manager](stubs/qiskit_fermions.transpiler.presets.generate_preset_jw_pass_manager.html.md): Generates a preset transpiler pipeline based on the `jordan_wigner()` mapping.
- [Linear Algebra Utilities](pydoc/qiskit_fermions.linalg.html.md): Linear algebra utilities, such as Givens decompositions of orbital rotations and Slater determinants.
- [givens_decomposition](stubs/qiskit_fermions.linalg.givens_decomposition.html.md): Decomposes a unitary matrix into Givens rotations and diagonal phases.
- [givens_decomposition_slater](stubs/qiskit_fermions.linalg.givens_decomposition_slater.html.md): Decomposes the occupied orbitals of a Slater determinant into Givens rotations.
- [Protocols](pydoc/qiskit_fermions.protocols.html.md): Protocols used throughout the package, for example for operators that convert to other representations, compute commutators, or apply a unitary.
- [SupportsApplyUnitaryPlaced](stubs/qiskit_fermions.protocols.SupportsApplyUnitaryPlaced.html.md): A package-specific extension of `ffsim.SupportsApplyUnitary`.
- [SupportsCommutators](stubs/qiskit_fermions.protocols.SupportsCommutators.html.md): A Protocol indicating support for efficient commutator generation.
- [SupportsFermionOperator](stubs/qiskit_fermions.protocols.SupportsFermionOperator.html.md): This package’s operator-conversion contract, converting an operator to a `FermionOperator`.
- [SupportsMajoranaOperator](stubs/qiskit_fermions.protocols.SupportsMajoranaOperator.html.md): An equivalent of the `SupportsFermionOperator` protocol, targeting Majorana operators.
- [Optional Dependencies](pydoc/qiskit_fermions.utils.optionals.html.md): Lazy availability testers for the optional third-party dependencies of qiskit-fermions.
- [`qiskit-fermions` C API reference](cdoc/index.html.md): Reference for the C API of qiskit-fermions, covering operator representations, mappers, and miscellaneous items.
- [Operator Representations](cdoc/qf-operators.html.md): The C API provides various data structures for representing fermionic operators in different bases.
- [QfFermionOperator](cdoc/qf-ferm-op.html.md): A spin-less fermionic operator.
- [QfMajoranaOperator](cdoc/qf-maj-op.html.md): A Majorana fermion operator.
- [QfEdgeVertexOperator](cdoc/qf-edge-op.html.md): An edge-vertex operator.
- [QfTransferVertexOperator](cdoc/qf-transfer-op.html.md): A transfer-vertex operator.
- [Operator Library](cdoc/qf-operators-library.html.md): The C API provides various functions to simplify the construction of commonly used operators.
- [Commutator Generators](cdoc/qf-commutators.html.md): C API functions that compute the commutator, anti-commutator, and double commutator of operator representations.
- [Electronic Integrals](cdoc/qf-electronic-integrals.html.md): C API constructor functions that build electronic structure Hamiltonians from integral coefficients in several layouts (tril, full, spin, and sym).
- [FCIDump](cdoc/qf-fcidump.html.md): An electronic structure Hamiltonian in FCIDump format.
- [Operator Terms](cdoc/qf-operators-terms.html.md): C API functions that operate on the individual terms of an operator, to group, filter, and order them.
- [Grouping Functions](cdoc/qf-operators-terms-grouping.html.md): C API functions that assign operator terms to groups automatically and that analyze an existing grouping.
- [Filtering Functions](cdoc/qf-operators-terms-filtering.html.md): Filters out the terms of an operator that are diagonal in the occupation-number basis.
- [Ordering Functions](cdoc/qf-operators-terms-ordering.html.md): C API functions that reorder the terms of an operator, either canonically or by group index.
- [Mapper Library](cdoc/qf-mappers-library.html.md): C API functions that map operators to qubit operators with the Jordan-Wigner and ternary-tree encodings, and that convert between operator representations.
- [Ternary Trees](cdoc/qf-ternary-tree.html.md): C API for ternary trees, which define fermion-to-qubit encodings of N fermionic modes onto N qubits: construct a tree and query the resulting encoding.
- [Various](cdoc/qf-various.html.md): Miscellaneous items of the C API, such as return codes.
- [QfExitCode](cdoc/qf-exit-code.html.md): Integer exit codes returned to C.
- [Release Notes](release-notes.html.md): Release notes of Qiskit Fermions for each release, covering both the Python API and the C API.