Real-Time Decoding for Fault-Tolerant Quantum Computing: Towards higher decoding speed and lower communication latency

Real-time decoding at the logical clock speed will be essential for universal fault-tolerant quantum computers. However, the short QEC cycle (<1 microsecond for superconducting qubits) poses enormous challenges. We examine the two issues that need to be addressed to overcome that: decoding speed and communication latency. We illustrate a review of current efforts on decoder algorithms and perspectives for the next few years aimed at achieving sufficient speed while maintaining good accuracy. In particular, we discuss the challenges at the level of the algorithm itself, its applicability (quantum memory, lattice surgery), the software stack, computational resources (FPGA/ASIC), as well as codesign across these aspects.

To address the communication-latency issue, Qblox proposes and implements a distributed control-stack architecture where measurement outcomes and Pauli-frame updates are shared within a few hundreds of nanoseconds. This architecture includes and interfaces to a specialized module for running user-defined decoding algorithms.