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arXiv · 2411.15612

Faulty towers: recovering a functioning quantum random access memory in the presence of defective routers

D. K. Weiss·Shifan Xu·Shruti Puri·Yongshan Ding·S. M. Girvin
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Abstract

Proposals for quantum random access memory (QRAM) generally have a binary-tree structure, and thus require hardware that is exponential in the depth of the QRAM. For solid-state based devices, a fabrication yield that is less than $100\%$ implies that certain addresses at the bottom of the tree become inaccessible if a router in the unique path to that address is faulty. We discuss how to recover a functioning QRAM in the presence of faulty routers. We present the \texttt{IterativeRepair} algorithm, which constructs QRAMs layer by layer until the desired depth is reached. This algorithm utilizes ancilla flag qubits which reroute queries to faulty routers. We present a classical algorithm \texttt{FlagQubitMinimization} that attempts to minimize the required number of such ancilla. For a router failure rate of $1\%$ and a QRAM of depth $n=13$, we expect that on average 430 addresses need repair: we require only 1.5 ancilla flag qubits on average to perform this rerouting.

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D. K. Weiss, Shifan Xu, Shruti Puri, Yongshan Ding, S. M. Girvin. 2024-11-23. Faulty towers: recovering a functioning quantum random access memory in the presence of defective routers. https://arxiv.org/abs/2411.15612

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