What is ancilla qubits?

Ancilla qubits are additional qubits used in quantum computing algorithms to improve the accuracy and error correction of the computations. They are used to assist in the correction of errors that occur during the computation process by measuring the state of the ancilla qubit and comparing it to the state of the other qubits. If there is a discrepancy, the computational process is rerun until the error is corrected. Ancilla qubits are also used in quantum teleportation, where they assist in the transfer of quantum information from one qubit to another over large distances.