论文标题

大规模哈密顿动力学的局部变异量子汇编

Local variational quantum compilation of a large-scale Hamiltonian dynamics

论文作者

Mizuta, Kaoru, Nakagawa, Yuya O., Mitarai, Kosuke, Fujii, Keisuke

论文摘要

在量子电路上实施时间演化运算符对于量子模拟很重要。但是,标准方式,小动物,需要大量的大门才能达到理想的准确性。在这里,我们提出了一种局部变分量子汇编(LVQC)算法,该算法允许通过使用较小尺寸的量子系统进行优化,可以准确有效地在大规模量子系统上精确编译时间演化运算符。 LVQC使用了一个子系统成本函数,该子系统成本函数近似于整个电路的保真度,该函数定义为每个子系统的大小,如Lieb-Robinson(LR)结合带来的近似因果锥。我们严格地针对子系统的大小来得出其缩放属性,并表明在子系统大小上进行的优化导致了整个系统时间演变运算符的汇编。结果,LVQC使用有限尺寸的量子计算机或可以处理如此较小的量子系统的经典模拟器运行。例如,可以使用$ O(l^0)$ - 或$ O(\ log L)$ - 大小量子系统来编译有限范围且短额的交互$ l $ size系统,具体取决于观察到的感兴趣。此外,由于这种形式主义仅依赖于LR结合,因此它可以在涉及有限,短和长度相互作用的通用维度中有效地构建各种系统的时间演化运算符。我们还在数值上证明了一维系统的LVQC算法。通过时间不断发展的块拆卸,我们成功地压缩了汇编以$ 20 $ QUBITS来压缩高达$ 40 $ QUBITS的时间演化操作员的深度。 LVQC不仅提供了设计大型量子电路的经典协议,而且还将阐明中等规模量子设备在实现大型量子设备中实现算法时的应用。

Implementing time evolution operators on quantum circuits is important for quantum simulation. However, the standard way, Trotterization, requires a huge numbers of gates to achieve desirable accuracy. Here, we propose a local variational quantum compilation (LVQC) algorithm, which allows to accurately and efficiently compile a time evolution operators on a large-scale quantum system by the optimization with smaller-size quantum systems. LVQC utilizes a subsystem cost function, which approximates the fidelity of the whole circuit, defined for each subsystem as large as approximate causal cones brought by the Lieb-Robinson (LR) bound. We rigorously derive its scaling property with respect to the subsystem size, and show that the optimization conducted on the subsystem size leads to the compilation of whole-system time evolution operators. As a result, LVQC runs with limited-size quantum computers or classical simulators that can handle such smaller quantum systems. For instance, finite-ranged and short-ranged interacting $L$-size systems can be compiled with $O(L^0)$- or $O(\log L)$-size quantum systems depending on observables of interest. Furthermore, since this formalism relies only on the LR bound, it can efficiently construct time evolution operators of various systems in generic dimension involving finite-, short-, and long-ranged interactions. We also numerically demonstrate the LVQC algorithm for one-dimensional systems. Employing classical simulation by time-evolving block decimation, we succeed in compressing the depth of a time evolution operators up to $40$ qubits by the compilation for $20$ qubits. LVQC not only provides classical protocols for designing large-scale quantum circuits, but also will shed light on applications of intermediate-scale quantum devices in implementing algorithms in larger-scale quantum devices.

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