---
title: library (latest version)
description: API reference for qiskit_fermions.circuit.library in the latest version of qiskit-fermions
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-fermions/circuit-library
---

# Circuit Library

This module provides a library of [`FermionicGate`](/docs/api/qiskit-fermions/circuit-fermionic-gate#qiskit_fermions.circuit.FermionicGate "qiskit_fermions.circuit.FermionicGate") implementations.

|                                                                                                                                                                                                                                         |                                                                           |
| --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------- |
| [`Evolution`](/docs/api/qiskit-fermions/circuit-library-evolution#qiskit_fermions.circuit.library.Evolution "qiskit_fermions.circuit.library.Evolution")(num\_modes, operator\[, time])                                                 | Implements the time evolution of an operator.                             |
| [`InitializeModes`](/docs/api/qiskit-fermions/circuit-library-initialize-modes#qiskit_fermions.circuit.library.InitializeModes "qiskit_fermions.circuit.library.InitializeModes")(occupation)                                           | Prepares (or, under simulation, certifies) a fermionic mode occupation.   |
| [`OrbitalRotation`](/docs/api/qiskit-fermions/circuit-library-orbital-rotation#qiskit_fermions.circuit.library.OrbitalRotation "qiskit_fermions.circuit.library.OrbitalRotation")(rotation\_unitary)                                    | Implements an orbital rotation.                                           |
| [`PrepareSlaterDeterminant`](/docs/api/qiskit-fermions/circuit-library-prepare-slater-determinant#qiskit_fermions.circuit.library.PrepareSlaterDeterminant "qiskit_fermions.circuit.library.PrepareSlaterDeterminant")(occupation, ...) | Prepares a Slater determinant from an occupation and an orbital rotation. |
| [`UCC`](/docs/api/qiskit-fermions/circuit-library-ucc#qiskit_fermions.circuit.library.UCC "qiskit_fermions.circuit.library.UCC")(variant, t1, t2, \*\[, antisymmetric, atol])                                                           | Implements the unitary coupled cluster (UCC) ansatz.                      |
| [`UCJ`](/docs/api/qiskit-fermions/circuit-library-ucj#qiskit_fermions.circuit.library.UCJ "qiskit_fermions.circuit.library.UCJ")(variant, diag\_coulomb\_mats, ...\[, ...])                                                             | Implements the (local) unitary cluster Jastrow ((L)UCJ) ansatz.           |