<a id="module-qiskit_fermions.operators"></a>

# Operator Representations

This module provides various data structures for representing fermionic operators in different
bases.

## Fermion Operator

This operator represents fermionic operators in terms of the second-quantization creation and
annihilation operators.

## Majorana Operator

This operator represents fermionic operators in terms of Majorana fermions.

## Interaction Operators

Many commonly used operators can be expressed as interaction operators which can express operators
with even fermionic parity. Such operators are defined in terms of pairs of Majorana actions
$\gamma_k\gamma'_k$ or, equivalently, are generated by the quadratic fermionic operators
$a_i a_j$, $a_i^\dagger a_j$, $a_i a^\dagger_j$, and $a^\dagger_i
a^\dagger_j$.

This package provides two different data structures expressing operators of this type in terms of
Hermitian generators: