Leakage Reduction Protocol in Exchange-Only Qubits

Exchange-only qubits in Si/SiGe quantum dots are a promising platform for quantum information processing. This approach encodes a qubit in a logical subsystem in a three-spin system, and accordingly requires mitigation of leakage from the encoded space. Here, we present the first demonstration of a Leakage Reduction Unit (LRU) for exchange-only qubits. The LRU returns leaked states to the encoded space through a Reset-If-Leaked exchange sequence and consumption of initialized ancilla spins. The protocol utilizes mid-circuit initialization, which is another first for this platform. We apply a variety of characterization and benchmarking techniques to quantify the fidelity and leakage reduction efficacy of our LRU implementation. This work validates an important operation for the exchange-only qubit architecture.