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Qualifying Exam

AutoBraid: A Framework for Enabling Efficient Surface Communication in Quantum Computing


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Monday, September 13, 2021, 10:00am - 11:30am


Speaker: Fei Hua

Location : Remote via Zoom


Prof. Zheng Zhang (advisor)

Prof. Mario Szegedy

Prof. Yipeng Huang

Prof. Sungjin Ahn

Event Type: Qualifying Exam

Abstract: Quantum computers can solve problems that are even intractable using the most powerful state-of-the-art classical computer. However, qubits are fickle and error prone. It is necessary to actively correct errors in the execution of a quantum circuit. Quantum error correction (QEC) codes are proposed to ensure the fault-tolerant computing. With the QEC, one logical circuit is compiled into an encoded circuit. Most studies on quantum circuit compilation focus on NISQ devices which have 10-100 qubits and are not fault-tolerant. In this paper, we focus on the compilation for the fault-tolerant quantum hardware. In particular, we focus on optimizing \emph{communication parallelism} for the \emph{surface code} based QEC. The compilation for surface code involves non-trivial geometric manipulation of a large lattice of entangled physical qubits. Communication between qubits is the major bottleneck. A two-qubit gate in surface code is implemented as a virtual "pipe” in space-time called a braiding path. The braiding paths should be carefully routed to avoid congestion. We provide a framework for efficiently scheduling braiding paths. We discover that for quantum programs with a local parallelism pattern, our framework guarantees an optimal solution, while the previous greedy-heuristic-based solution cannot. Moreover, we propose an extension on the local parallelism analysis framework to address the communication bottleneck. Our framework achieves orders of magnitude improvement after addressing the communication bottleneck.


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