Virtualized Logical Qubits: A 2.5D Architecture for Error-Corrected Quantum Computing (2009.01982v1)

Abstract: 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.

• The paper demonstrates that virtualizing logical qubits in a 2.5D layout maintains fault tolerance with minimal performance loss.
• It achieves transversal CNOT operations up to 6x faster and requires 10x fewer transmons than traditional 2D architectures.
• Simulations confirm efficient magic state production and scalable error correction, underscoring its potential for practical quantum computing.

Overview of 2.5D Architecture for Error-Corrected Quantum Computing

The paper titled "Virtualized Logical Qubits: A 2.5D Architecture for Error-Corrected Quantum Computing" explores a significant step forward in designing practical quantum computing architectures. As quantum devices progress from demonstrating quantum supremacy to achieving greater reliability through error correction, the authors propose utilizing a 2.5D architecture that enhances both performance and compactness through the virtualization of logical qubits within quantum memory.

The foundational premise of the paper is leveraging a 2.5D architecture in which quantum logical qubits are virtualized across multiple qubit memories, specifically using resonant cavities attached to transmon qubits. This approach can result in substantial hardware savings and performance gains by implementing surface codes efficiently. The non-intuitive finding that distributing logical qubits across various memory layers has negligible impact on fault tolerance underpins the central contribution of this work.

The architecture allows for faster quantum operations through transversal CNOTs, which are 6x faster than lattice surgery-based CNOT operations. Notably, the architecture achieves a 10x reduction in the need for transmons compared to traditional 2D architectures and saves an additional 2x with an optimization towards compactness. While there is a 10x penalty in serialization, the overall design maintains competitive fault tolerance and performance metrics compared to existing two-dimensional transmon-only counterparts.

The paper's claims are supported by simulations demonstrating that the proposed system can achieve fault-tolerance levels equivalent to conventional two-dimensional grids while significantly reducing hardware requirements. By achieving a magic state production rate of 1.22 times that of the baseline rate, this architecture addresses an essential component of future fault-tolerant quantum computers, which is the continuous need for producing magic states. These states are vital for universal quantum computation, enabling complex algorithms like Shor's and Grover's to execute efficiently.

The 2.5D architecture presented is projected to make quantum computing more accessible and feasible by reducing the hardware footprint required for error-corrected quantum computation. The authors propose that a proof-of-concept with around 10 logical qubits can be achieved with just 11 transmons and 9 attached cavities, further reinforcing the practicality and scalability of their design.

The implications of this research are profound, as the pursuit of more compact and efficient quantum architectures aligns with the broader goal of realizing practical, fault-tolerant quantum computers. This work provides a substantial foundation for future developments and potentially accelerates the path forward for quantum technology advancements. Future work may explore further optimizations in error correction techniques and the potential integration of such architectures into existing quantum computational frameworks.