TimeStitch: Exploiting Slack to Mitigate Decoherence in Quantum Circuits*

The coupling of qubits to their environment causes decoherence, adding significant noise to computation; thus, methods for combatting decoherence are needed to increase the performance of quantum algorithms on near-term machines. While many forms of error mitigation rely on adding extra gates to a circuit, calibrating new gates, or extending a circuit's runtime, this work leverages the gates already present in quantum programs. We exploit circuit slack, a common feature in compiled quantum circuits, and schedule single-qubit gates to counteract some errors. 

Theory fails to capture all noise sources in NISQ devices, requiring practical solutions that better minimize unpredictable errors. Here, we present a technique that leverages quantum reversibility with novel slice-inverse tuning to pinpoint the optimum execution of single-qubit gates within circuits. When slack optimization is implemented as a compilation pass, quantum circuits on real machines experience fidelity boosts without violating critical path frontiers in the slack tuning procedures or in the final rescheduled circuit.