Running quantum algorithms protected by quantum error correction requires a real time, classical decoder. To prevent the accumulation of a backlog, this decoder must process syndromes from the quantum device at a faster rate than they are generated. Most prior work on real time decoding has focused on an isolated logical qubit encoded in the surface code. However, for surface code, quantum programs of utility will require multi-qubit interactions performed via lattice surgery. A large merged patch can arise during lattice surgery -- possibly as large as the entire device. This puts a significant strain on a real time decoder, which must decode errors on this merged patch and maintain the level of fault-tolerance that it achieves on isolated logical qubits. These requirements are relaxed by using spatially parallel decoding, which can be accomplished by dividing the physical qubits on the device into multiple overlapping groups and assigning a decoder module to each. We refer to this approach as spatially parallel windows. While previous work has explored similar ideas, none have addressed system-specific considerations pertinent to the task or the constraints from using hardware accelerators. In this work, we demonstrate how to configure spatially parallel windows, so that the scheme (1) is compatible with hardware accelerators, (2) supports general lattice surgery operations, (3) maintains the fidelity of the logical qubits, and (4) meets the throughput requirement for real time decoding. Furthermore, our results reveal the importance of optimally choosing the buffer width to achieve a balance between accuracy and throughput -- a decision that should be influenced by the device's physical noise.

翻译：运行由量子纠错保护的量子算法需要实时经典解码器。为避免错误累积导致延迟，该解码器必须以快于量子设备生成综合征的速度处理这些数据。现有实时解码研究多聚焦于表面码编码的孤立逻辑量子比特，但实用量子程序需要通过晶格手术实现多量子比特交互。晶格手术过程中可能出现大规模合并修补区——其规模甚至可达整个设备。这给实时解码器带来巨大压力，它需解码合并修补区上的错误，并维持在孤立逻辑量子比特上实现的容错水平。通过空间并行解码可缓解这些需求，具体方法是将设备上的物理量子比特划分为多个重叠组，并为每组分配一个解码器模块。我们称此方法为"空间并行窗口"。尽管已有研究探索类似概念，但均未涉及该项任务特有的系统布局考量或硬件加速器的约束。本文演示如何配置空间并行窗口，使该方案：(1)兼容硬件加速器，(2)支持通用晶格手术操作，(3)保持逻辑量子比特保真度，(4)满足实时解码的吞吐量需求。此外，我们的结果揭示了优化选择缓冲宽度以平衡精度与吞吐量的重要性——该决策应受设备物理噪声特性的影响。