Uncomputing Ancilla Qubits in Quantum Circuits

Uncomputation of ancilla qubits is essential in quantum computing to reset auxiliary qubits to a zero state, ensuring their safe discarding and reducing resource overhead. Current methods for uncomputation either rely on manual procedures or use additional ancilla qubits to store intermediate computation results, which increases qubit storage requirements. Additionally, most in-place uncomputation techniques employ an all-or-nothing strategy, wherein they perform uncomputation only when all ancilla qubits in the given circuit can be uncomputed.In this work, we tackle the problem of uncomputing a maximum number of ancilla qubits in a quantum circuit with minimal qubit storage overhead. We propose a novel approach where partial uncomputation - reverting the last 'm' gates - enables the uncomputation of more qubits. We present three algorithms designed to uncompute the largest possible set of ancilla qubits and demonstrate their effectiveness through experiments on various randomly generated quantum circuits.