论文标题

仅使用Clifford电路的迭代量子耦合群集

Iterative Qubit Coupled Cluster using only Clifford circuits

论文作者

Brown, James, Coons, Marc P., Lloyd, Erika, Fleury, Alexandre, Bieniasz, Krzysztof, Senicourt, Valentin, Zaribafiyan, Arman

论文摘要

量子算法的基础能量估计的性能直接受到初始状态的质量的影响,在这种状态下,质量是根据输入状态与目标状态的重叠来定义的。理想的状态制备方案可以通过易于经典生成,并可以将其转换为量子电路,而量子电路的开销很小,同时与给定的哈密顿量的靶向特征态具有显着的重叠。我们提出了一种通过引入迭代Qubit耦合群集(IQCC)方法的变体来满足这些要求的方法,该方法仅使用Clifford电路。这些电路可以在经典计算机上有效模拟,并根据Gottesman-Knill定理进行多项式缩放。由于IQCC方法是作为量子算法开发的,因此我们的变体可以自然映射到量子硬件。我们还对算法进行了几种优化,从而增强了其可扩展性。我们证明了该算法在小分子(例如H2,Lih和H2O)的基态模拟中的正确性,并将我们的研究扩展到具有钛基化合物Ti(C5H5)(CH3)3(20,20)活性空间的复杂系统,需要40吨。结果表明,该算法的收敛性很好,并且可以准确地表示基态。此外,我们显示了一个自动化工作流程,用于限制量子空间空间,从而通过考虑仅考虑受非平凡操作影响的量子位来减轻计算资源。

The performance of quantum algorithms for ground-state energy estimation is directly impacted by the quality of the initial state, where quality is traditionally defined in terms of the overlap of the input state with the target state. An ideal state preparation protocol can be characterized by being easily generated classically and can be transformed to a quantum circuit with minimal overhead while having a significant overlap with the targeted eigenstate of a given Hamiltonian. We propose a method that meets these requirements by introducing a variant of the iterative qubit coupled cluster (iQCC) approach, which exclusively uses Clifford circuits. These circuits can be efficiently simulated on a classical computer, with polynomial scaling according to the Gottesman-Knill theorem. Since the iQCC method has been developed as a quantum algorithm firstly, our variant can be mapped naturally to quantum hardware. We additionally implemented several optimizations to the algorithm enhancing its scalability. We demonstrate the algorithm's correctness in ground-state simulations for small molecules such as H2, LiH, and H2O, and extend our study to complex systems like the titanium-based compound Ti(C5H5)(CH3)3 with a (20, 20) active space, requiring 40 qubits. Results show that the convergence of the algorithm is well-behaved, and the ground state can be represented accurately. Moreover, we show an automated workflow for restricting the qubit active space, thus relieving computational resources by considering only qubits affected by non-trivial operations.

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