---
title: AncillaQubit (v1.0)
description: API reference for qiskit.circuit.AncillaQubit in qiskit v1.0
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/1.0/qiskit.circuit.AncillaQubit
---

# AncillaQubit

*class* `qiskit.circuit.AncillaQubit(register=None, index=None)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/1.0/qiskit/circuit/quantumregister.py#L60-L65)

Bases: [`Qubit`](/docs/api/qiskit/1.0/qiskit.circuit.Qubit "qiskit.circuit.quantumregister.Qubit")

A qubit used as ancillary qubit.

Creates a qubit.

**Parameters**

- **register** ([*QuantumRegister*](/docs/api/qiskit/1.0/qiskit.circuit.QuantumRegister "qiskit.circuit.QuantumRegister")) – Optional. A quantum register containing the bit.
- **index** ([*int*](https://docs.python.org/3/library/functions.html#int)) – Optional. The index of the bit in its containing register.

**Raises**

[**CircuitError**](/docs/api/qiskit/1.0/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – if the provided register is not a valid [`QuantumRegister`](/docs/api/qiskit/1.0/qiskit.circuit.QuantumRegister "qiskit.circuit.QuantumRegister")