Improving syndrome detection using quantum optimal control

In order to achieve fault-tolerant quantum computation, it will be necessary to continuously correct errors using quantum error correcting codes. To meet this goal, it will be crucial to continue to develop better codes and decoders, as well as to improve the implementations of basic building blocks of error correction, such as stabilizer circuits and parity check operations, on real NISQ-stage devices available today. Here, we present recent results along these lines. First, we demonstrate that the fidelity of small-scale quantum error correcting codes can be improved using our deterministic error-suppression workflow, which is designed to reduce non-Markovian noise from a variety of sources using error-aware compilation, system-wide gate optimization, dynamical decoupling, and measurement-error mitigation. Results obtained using our workflow are consistently better than the default pipeline: we find improved error detection success rates which are 2.5 and 3.3 times higher compared to the default approach. Second, we introduce a faster implementation of the 2-qubit parity check operation and then use quantum optimal control techniques to calibrate this operation. This approach allows for improved parity checks that have both a higher fidelity and shorter duration than the standard implementation based on multiple two-qubit controlled gates.