Operating on the principles of quantum mechanics, quantum algorithms hold the promise for solving problems that are beyond the reach of the best-available classical algorithms. An integral part of realizing such speedup is the implementation of quantum queries, which read data into forms that quantum computers can process. Quantum random access memory (QRAM) is a promising architecture for realizing quantum queries. However, implementing QRAM in practice poses significant challenges, including query latency, memory capacity and fault-tolerance. In this paper, we propose the first end-to-end system architecture for QRAM. First, we introduce a novel QRAM that hybridizes two existing implementations and achieves asymptotically superior scaling in space (qubit number) and time (circuit depth). Like in classical virtual memory, our construction enables queries to a virtual address space larger than what is actually available in hardware. Second, we present a compilation framework to synthesize, map, and schedule QRAM circuits on realistic hardware. For the first time, we demonstrate how to embed large-scale QRAM on a 2D Euclidean space, such as a grid layout, with minimal routing overhead. Third, we show how to leverage the intrinsic biased-noise resilience of the proposed QRAM for implementation on either Noisy Intermediate-Scale Quantum (NISQ) or Fault-Tolerant Quantum Computing (FTQC) hardware. Finally, we validate these results numerically via both classical simulation and quantum hardware experimentation. Our novel Feynman-path-based simulator allows for efficient simulation of noisy QRAM circuits at a larger scale than previously possible. Collectively, our results outline the set of software and hardware controls needed to implement practical QRAM.

翻译：基于量子力学原理的量子算法有望解决现有最优经典算法无法触及的问题。实现这种加速的关键组成部分是量子查询的实现——即将数据读取为量子计算机可处理的形式。量子随机存取存储器（QRAM）是实现量子查询的前沿架构。然而，在实践中部署QRAM面临着查询延迟、存储容量和容错性等重大挑战。本文提出首个端到端的QRAM系统架构。首先，我们设计了一种新型QRAM，该架构融合两种现有实现方案，在空间（量子比特数）和时间（电路深度）上实现了渐近更优的扩展性。如同经典虚拟存储器，我们的设计允许查询比硬件实际可用空间更大的虚拟地址空间。其次，我们提出一个编译框架，用于在真实硬件上合成、映射和调度QRAM电路。首次证明如何在二维欧几里得空间（如网格布局）中嵌入大规模QRAM，同时将布线开销降至最低。第三，我们展示了如何利用所提出QRAM的内在偏置噪声鲁棒性，使其适用于含噪声中等规模量子（NISQ）或容错量子计算（FTQC）硬件。最后，通过经典仿真和量子硬件实验对结果进行数值验证。我们创新的基于费曼路径的模拟器能够以超越以往可能性的规模高效模拟含噪QRAM电路。综合而言，我们的研究结果勾勒出了实现实用化QRAM所需的软硬件控制方案。