Pinball: A Cryogenic Predecoder for Quantum Error Correction Decoding under Circuit-Level Noise

Scaling fault tolerant quantum computers, especially cryogenic systems based on the surface code, to millions of qubits is very challenging due to poorly-scaling data processing and power consumption overheads. One key challenge is the design of decoders for real-time quantum error correction (QEC), which demands high data rates for error processing; this is particularly apparent in systems with cryogenic qubits and room temperature (RT) decoders. In response, cryogenic predecoding using lightweight logic has been proposed to handle common, sparse errors within the cryogenic domain. However, prior work only accounts for a subset of the error sources present in real-world quantum systems with limited accuracy, often degrading performance below a useful level in practical scenarios. Furthermore, prior reliance on SFQ logic precludes detailed architecture-technology co-optimization. To address these shortcomings, this paper introduces Pinball(1), a comprehensive design in cryogenic CMOS of a QEC predecoder for the surface code, tailored to realistic, circuit-level noise. By accounting for error generation and propagation through QEC circuits, our design achieves higher predecoding accuracy, outperforming logical error rates of the current state-of-theart cryogenic predecoder by nearly six orders of magnitude. Remarkably, despite operating under much stricter power and area constraints, Pinball also reduces logical error rates by 32.58x and 5x, respectively, compared to the state-of-the-art RT predecoder and an RT ensemble configuration. By increasing cryogenic coverage, we also reduce syndrome bandwidth up to 3780.72x. Through co-design with 4 K-characterized 22nm FDSOI technology, we achieve a peak power consumption under 0.56mW. Voltage/frequency scaling and body biasing enable 22.2x lower typical power consumption, yielding up to 67.4x total energy savings. Assuming a 4K power budget of 1.5W, our predecoder can support up to 2,668 logical qubits at d = 21.