Efficient learning of $t$-doped stabilizer states with single-copy measurements

Nai-Hui Chia1, Ching-Yi Lai2, and Han-Hsuan Lin3

1Department of Computer Science, Rice University, TX 77005-1892, United States
2Institute of Communications Engineering, National Yang Ming Chiao Tung University, Hsinchu 300093, Taiwan
3Department of Computer Science, National Tsing Hua University, Hsinchu 30013, Taiwan

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Abstract

One of the primary objectives in the field of quantum state learning is to develop algorithms that are time-efficient for learning states generated from quantum circuits. Earlier investigations have demonstrated time-efficient algorithms for states generated from Clifford circuits with at most $\log(n)$ non-Clifford gates. However, these algorithms necessitate multi-copy measurements, posing implementation challenges in the near term due to the requisite quantum memory. On the contrary, using solely single-qubit measurements in the computational basis is insufficient in learning even the output distribution of a Clifford circuit with one additional $T$ gate under reasonable post-quantum cryptographic assumptions. In this work, we introduce an efficient quantum algorithm that employs only nonadaptive single-copy measurement to learn states produced by Clifford circuits with a maximum of $O(\log n)$ non-Clifford gates, filling a gap between the previous positive and negative results.

In the realm of quantum state learning, researchers aim to create time-efficient algorithms for understanding states generated by quantum circuits. Previous studies achieved efficiency for states from Clifford circuits with limited non-Clifford gates, but these required challenging multi-copy measurements, hindering near-term implementation. This work presents a groundbreaking quantum algorithm that, with just single-copy measurements, efficiently learns states from Clifford circuits featuring up to $O(\log(n))$ non-Clifford gates. This bridges the gap between earlier positive and negative results, offering a promising solution with practical implications for quantum computing.

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