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

# ann

`ann(mode)`

Constructs an annihilation action on the fermionic mode at `mode`.

**Parameters**

**mode** ([*int*](https://docs.python.org/3/library/functions.html#int)) – the spin-less fermionic mode on which to act.

**Returns**

An annihilation [`FermionAction`](/docs/api/qiskit-fermions/operators-fermion-action-fermion-action "qiskit_fermions.operators.fermion_action.FermionAction") on `mode`.

**Return type**

[tuple](https://docs.python.org/3/library/stdtypes.html#tuple)\[[bool](https://docs.python.org/3/library/functions.html#bool), [int](https://docs.python.org/3/library/functions.html#int)]