Readout Error Mitigation for Mid-Circuit Measurements and Feedforward

Abstract: Current quantum computing platforms suffer from readout errors, where faulty measurement outcomes are reported by the device. These errors are particularly harmful in quantum programs that rely on branch statements wherein operations in later parts of the program are dynamically determined by mid-circuit measurements. We propose a general protocol for mitigating mid-circuit measurement errors in the presence of feedforward, offering an efficient solution that works for any number of feedforward layers without increasing circuit depth or two-qubit gate counts, making it highly suitable for noisy intermediate-scale quantum (NISQ) devices. Our method demonstrates up to a ${\sim} 60\%$ reduction in error on superconducting quantum processors across several practically relevant feedforward circuits, including dynamic qubit resets, shallow-depth GHZ state preparation, and multi-stage quantum teleportation. This work paves the way for more resilient adaptive quantum circuits, crucial for both current and future quantum computing applications.