  Many quantum algorithms make use of ancilla, additional qubits used to store
temporary information during computation, to reduce the total execution time.
Quantum computers will be resource-constrained for years to come so reducing
ancilla requirements is crucial. In this work, we give a method to generate
ancilla out of idle qubits by placing some in higher-value states, called
qudits. We show how to take a circuit with many $O(n)$ ancilla and design an
ancilla-free circuit with the same asymptotic depth. Using this, we give a
circuit construction for an in-place adder and a constant adder both with
$O(\log n)$ depth using temporary qudits and no ancilla.

Quantum Physics;Emerging Technologies