论文标题

具有连贯的多开始优化的量子回路的有效变异合成

Efficient variational synthesis of quantum circuits with coherent multi-start optimization

论文作者

Nemkov, Nikita A., Kiktenko, Evgeniy O., Luchnikov, Ilia A., Fedorov, Aleksey K.

论文摘要

我们将变异量子电路合成的问题考虑到由CNOT门和任意单量(1Q)门组成的门集,主要目标是最小化CNOT计数。首先,我们注意到,由于复杂性的组合爆炸的离散架构搜索,由于局部最低限度的无所不知,因此1Q门上的优化也可能是一个至关重要的障碍(在变异构造的背景下,在变异量子量算法的背景下众所周知,但显然是在变化汇编中被低估的)。认真对待这个问题,我们对初始条件进行了广泛的搜索,这是我们方法的重要组成部分。我们建议的另一个关键思想是使用参数化的两量(2Q)控制的相位门,它可以在身份门和CNOT门之间插值,并允许对离散体系结构搜索的连续放松,可以在1Q门上以优化的方式共同执行。对体系结构的这种连贯的优化与1Q门一起在实践中似乎表现出色,有时甚至超过了1Q门(对于固定的最佳体系结构)的优势。 As illustrative examples and applications we derive 8 CNOT and T depth 3 decomposition of the 3q Toffoli gate on the nearest-neighbor topology, rediscover known best decompositions of the 4q Toffoli gate on all 4q topologies including a 1 CNOT gate improvement on the star-shaped topology, and propose decomposition of the 5q Toffoli gate on the nearest-neighbor topology with 48 CNOT gates.我们还通过IBM_QX_MAPPED数据库的许多5Q量子电路进行方法的性能,这表明它与现有软件具有很高的竞争力。这项工作中开发的算法可作为Python软件包CPFlow提供。

We consider the problem of the variational quantum circuit synthesis into a gate set consisting of the CNOT gate and arbitrary single-qubit (1q) gates with the primary target being the minimization of the CNOT count. First we note that along with the discrete architecture search suffering from the combinatorial explosion of complexity, optimization over 1q gates can also be a crucial roadblock due to the omnipresence of local minimums (well known in the context of variational quantum algorithms but apparently underappreciated in the context of the variational compiling). Taking the issue seriously, we make an extensive search over the initial conditions an essential part of our approach. Another key idea we propose is to use parametrized two-qubit (2q) controlled phase gates, which can interpolate between the identity gate and the CNOT gate, and allow a continuous relaxation of the discrete architecture search, which can be executed jointly with the optimization over 1q gates. This coherent optimization of the architecture together with 1q gates appears to work surprisingly well in practice, sometimes even outperforming optimization over 1q gates alone (for fixed optimal architectures). As illustrative examples and applications we derive 8 CNOT and T depth 3 decomposition of the 3q Toffoli gate on the nearest-neighbor topology, rediscover known best decompositions of the 4q Toffoli gate on all 4q topologies including a 1 CNOT gate improvement on the star-shaped topology, and propose decomposition of the 5q Toffoli gate on the nearest-neighbor topology with 48 CNOT gates. We also benchmark the performance of our approach on a number of 5q quantum circuits from the ibm_qx_mapping database showing that it is highly competitive with the existing software. The algorithm developed in this work is available as a Python package CPFlow.

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