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arXiv 2402.13754quant-phcs.AIcs.LG
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面向变分量子算法的强化学习辅助量子架构搜索

Reinforcement learning-assisted quantum architecture search for variational quantum algorithms

Akash Kundu

AI总结:

本文提出基于强化学习的量子架构搜索方法,利用张量编码、搜索约束、提前终止和DDQN自动寻找短而准的变分量子电路,并在无噪声与含噪场景中验证其优势。

摘要:

含噪中等规模量子(NISQ)时代的一个重大障碍是识别可正常工作的量子电路。这些电路还必须遵守当前量子硬件限制所施加的约束。变分量子算法(VQA)是一类量子-经典优化算法,旨在应对当前可用量子设备中的这些挑战。然而,VQA的整体性能取决于变分电路的初始化策略、电路结构(也称为ansatz)以及代价函数的配置。本文聚焦电路结构,通过利用强化学习(RL)自动搜索变分电路的最优结构来提升VQA的性能。在本文中,电路的最优性通过评估其深度、门和参数的总数,以及其在求解给定问题时的准确率来确定。自动搜索最优量子电路的任务被称为量子架构搜索(QAS)。QAS中的大多数研究主要集中在无噪声场景。然而,噪声对QAS的影响仍未得到充分研究。在本文中,我们通过引入基于张量的量子电路编码、对环境动态施加限制以高效探索可能电路的搜索空间、用于引导智能体寻找更短电路的回合终止机制,以及采用ε-greedy策略以获得更好稳定性的双深度Q网络(DDQN)来解决该问题。在无噪声和含噪量子硬件上的数值实验表明,在处理多种VQA时,我们基于RL的QAS优于现有QAS。同时,本文提出的方法可以方便地调整,以解决广泛的其他VQA。

英文摘要:

A significant hurdle in the noisy intermediate-scale quantum (NISQ) era is identifying functional quantum circuits. These circuits must also adhere to the constraints imposed by current quantum hardware limitations. Variational quantum algorithms (VQAs), a class of quantum-classical optimization algorithms, were developed to address these challenges in the currently available quantum devices. However, the overall performance of VQAs depends on the initialization strategy of the variational circuit, the structure of the circuit (also known as ansatz), and the configuration of the cost function. Focusing on the structure of the circuit, in this thesis, we improve the performance of VQAs by automating the search for an optimal structure for the variational circuits using reinforcement learning (RL). Within the thesis, the optimality of a circuit is determined by evaluating its depth, the overall count of gates and parameters, and its accuracy in solving the given problem. The task of automating the search for optimal quantum circuits is known as quantum architecture search (QAS). The majority of research in QAS is primarily focused on a noiseless scenario. Yet, the impact of noise on the QAS remains inadequately explored. In this thesis, we tackle the issue by introducing a tensor-based quantum circuit encoding, restrictions on environment dynamics to explore the search space of possible circuits efficiently, an episode halting scheme to steer the agent to find shorter circuits, a double deep Q-network (DDQN) with an $ε$-greedy policy for better stability. The numerical experiments on noiseless and noisy quantum hardware show that in dealing with various VQAs, our RL-based QAS outperforms existing QAS. Meanwhile, the methods we propose in the thesis can be readily adapted to address a wide range of other VQAs.

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