--- title: Qiskit Fermions description: Documentation for the latest version of Qiskit Fermions source: https://quantum.cloud.ibm.com/docs/en/addons/qiskit-fermions --- # Qiskit Fermions `qiskit-fermions` extends the Qiskit SDK with tools for working on fermionic systems. Within its scope it provides the following: - Efficient data structures for the representation and manipulation of fermionic operators in different forms - A framework for implementing operator conversion methods (including fermion-to-qubit encodings) - A library of efficient implementations of common conversion methods - A framework and library of gates for expressing fermionic circuits - A transpilation pipeline integrated with the Qiskit transpiler process to synthesize fermionic circuits into qubit-based circuits Additionally, `qiskit-fermions` integrates with other tools of the ecosystem, such as: - [ffsim](https://qiskit-community.github.io/ffsim/) for efficient simulation of fermionic circuits ## Get started Several guides exist to help you get started with this package. For an overview of its breadth of features, visit the [1D Fermi-Hubbard guide](/docs/addons/qiskit-fermions/guides/1-d-fermi-hubbard). ## Use case examples Components of this package have been used in research related to the following papers: - The qDRIFT randomized circuit compilation in [\[1\]](#id3). - The fermion-to-qubit synthesis during the transpilation process in [\[2\]](#id4). ## Technical discussion ### Design intentions This package is deliberately designed to align with Qiskit: it builds on a core implemented in Rust and provides first-party language bindings to Python and C. Its API intends to draw parallels to Qiskit in order to seamlessly integrate into the workflows of users with experience in programming Qiskit. A core principle to the design of `qiskit-fermions` was the decoupling of its fermionic circuit representation from its qubitized form. To be more precise: the fermionic circuits are meaningful by themselves and do not require a mapping to qubit space to be interpretable. Furthermore, the fermionic circuit representation cannot make any assumptions about its fermion-to-qubit encoding applied later on. Consequently, while Jordan-Wigner retains a dominant position and role, it is not assumed to be the \_default\_ fermion-to-qubit encoding. ### Known issues As long as the Qiskit C API has not yet reached feature parity with its Python API, some components of this package remain exclusive to its Python API, too. This includes the entire circuit library ([`qiskit_fermions.circuit`](/docs/api/qiskit-fermions/circuit#module-qiskit_fermions.circuit "qiskit_fermions.circuit")) as well as transpiler passes ([`qiskit_fermions.transpiler`](/docs/api/qiskit-fermions/transpiler#module-qiskit_fermions.transpiler "qiskit_fermions.transpiler")). ### Future work - Migrate the circuit library and transpiler passes into the Rust core (and provide a C API for interacting with them) - Extend the library of efficient operator conversion implementations - Extend the library of efficient operator data structures ## Contributing The source code is available [on GitHub](https://github.com/Qiskit/qiskit-fermions). The developer guide is located at [CONTRIBUTING.md](https://github.com/Qiskit/qiskit-fermions/blob/main/CONTRIBUTING.md) in the root of this project’s repository. By participating, you are expected to uphold Qiskit’s [code of conduct](https://github.com/Qiskit/qiskit/blob/main/CODE_OF_CONDUCT.md). ## Citing this package If you use this package in your research, use the [CITATION.bib](https://github.com/Qiskit/qiskit-fermions/blob/main/CITATION.bib) file in this project’s repository to cite the appropriate reference(s). ## License [Apache License 2.0](https://github.com/Qiskit/qiskit-fermions/blob/main/LICENSE.txt) ## Deprecation policy This package follows [semantic versioning](https://semver.org/). Breaking changes are made only occasionally, to improve the user experience. When possible, old interfaces are kept and marked as deprecated for as long as they can co-exist with the new ones. Each substantial improvement, breaking change, or deprecation is documented in the [release notes](/docs/api/qiskit-fermions/release-notes). ## References \[[1](#id1)] Samuele Piccinelli, et al., [Quantum chemistry with provable convergence via randomized sample-based Krylov quantum diagonalization](https://arxiv.org/abs/2508.02578v2), arXiv:2508.02578 \[quant-ph]. \[[2](#id2)] Anthony Gandon, et al., [Stabilizer-based quantum simulation of fermion dynamics with local qubit encodings](https://arxiv.org/abs/2512.11418v2), arXiv:2512.11418 \[quant-ph]. ## Contents - - [Documentation Home](/docs/addons/qiskit-fermions) - Installation Instructions - [C](/docs/addons/qiskit-fermions/install-c) - [Python](/docs/addons/qiskit-fermions/install-py) - Guides - [Design principles of operator representations](/docs/addons/qiskit-fermions/guides/operators) - [Group operator terms: use the operator structure](/docs/addons/qiskit-fermions/guides/grouping) - [Map operator representations](/docs/addons/qiskit-fermions/guides/mappers) - [Work with fermionic circuits](/docs/addons/qiskit-fermions/guides/circuit) - [VQE optimization at the fermionic level](/docs/addons/qiskit-fermions/guides/vqe-outer-loop) - [Build an LUCJ ansatz](/docs/addons/qiskit-fermions/guides/lucj) - [Generate SqDRIFT circuits](/docs/addons/qiskit-fermions/guides/sqdrift) - [Generate Krylov time-evolution circuits (SKQD)](/docs/addons/qiskit-fermions/guides/skqd) - [Transpile fermionic circuits](/docs/addons/qiskit-fermions/guides/transpilation) - [Optimize Slater determinant preparation](/docs/addons/qiskit-fermions/guides/merge-slater-determinant) - [Simulate 1D Fermi-Hubbard dynamics with flow sets](/docs/addons/qiskit-fermions/guides/1-d-fermi-hubbard) - [Simulate 2D Fermi-Hubbard dynamics with flow sets](/docs/addons/qiskit-fermions/guides/2-d-fermi-hubbard) - [The ffsim simulation backend](/docs/addons/qiskit-fermions/guides/ffsim) - [GitHub](https://github.com/Qiskit/qiskit-fermions) - API reference - [Python API reference](https://quantum.cloud.ibm.com/docs/api/qiskit-fermions) - [C API reference](https://quantum.cloud.ibm.com/docs/api/qiskit-fermions-c) - [Release notes](/docs/api/qiskit-fermions/release-notes)