Current, near-term quantum devices have shown great progress in recent years culminating with a demonstration of quantum supremacy. In the medium-term, however, quantum machines will need to transition to greater reliability through error correction, likely through promising techniques such as surface codes which are well suited for near-term devices with limited qubit connectivity. We discover quantum memory, particularly resonant cavities with transmon qubits arranged in a 2.5D architecture, can efficiently implement surface codes with substantial hardware savings and performance/fidelity gains. Specifically, we *virtualize logical qubits* by storing them in layers distributed across qubit memories connected to each transmon. Surprisingly, distributing each logical qubit across many memories has a minimal impact on fault tolerance and results in substantially more efficient operations. Our design permits fast transversal CNOT operations between logical qubits sharing the same physical address which are 6x faster than lattice surgery CNOTs. We develop a novel embedding which saves ~10x in transmons with another 2x from an additional optimization for compactness. Although Virtualized Logical Qubits (VLQ) pays a 10x penalty in serialization, advantages in the transversal CNOT and area efficiency result in performance comparable to 2D transmon-only architectures. Our simulations show fault tolerance comparable to 2D architectures while saving substantial hardware. Furthermore, VLQ can produce magic states 1.22x faster for a fixed number of transmon qubits. This is a critical benchmark for future fault-tolerant quantum computers. VLQ substantially reduces the hardware requirements for fault tolerance and puts within reach a proof-of-concept experimental demonstration of around 10 logical qubits, requiring only 11 transmons and 9 attached cavities in total.

中文翻译：

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虚拟化逻辑量子位：用于纠错量子计算的 2.5D 架构

近年来，当前的近期量子器件取得了巨大进步，最终证明了量子霸权。然而，从中期来看，量子机器将需要通过纠错过渡到更高的可靠性，可能是通过有前途的技术，例如非常适合具有有限量子位连接性的近期设备的表面代码。我们发现量子存储器，特别是具有排列在 2.5D 架构中的 transmon 量子位的谐振腔，可以有效地实现表面代码，同时节省大量硬件并提高性能/保真度。具体来说，我们通过将逻辑量子位存储在分布在连接到每个 transmon 的量子位存储器的层中来*虚拟化逻辑量子位*。出奇，将每个逻辑量子位分布在许多内存中对容错的影响最小，并导致操作效率显着提高。我们的设计允许在共享相同物理地址的逻辑量子位之间进行快速横向 CNOT 操作，这比晶格手术 CNOT 快 6 倍。我们开发了一种新颖的嵌入，它通过额外的紧凑性优化节省了大约 10 倍的 transmons 和另外 2 倍。尽管虚拟化逻辑量子位 (VLQ) 在序列化方面付出了 10 倍的代价，但横向 CNOT 和面积效率方面的优势导致性能可与 2D transmon-only 架构相媲美。我们的模拟显示了与 2D 架构相当的容错性，同时节省了大量硬件。此外，对于固定数量的 transmon qubits，VLQ 可以以 1.22 倍的速度产生魔法状态。这是未来容错量子计算机的关键基准。VLQ 显着降低了容错的硬件要求，并实现了大约 10 个逻辑量子位的概念验证实验演示，总共只需要 11 个传输器和 9 个附加腔。