Quantum Simulation of Molecular Dynamics ProcessesA Benchmark Study Using a Classical Simulator and Present-Day Quantum Hardware

We explore how the fundamental problems in quantum molecular dynamics can be modeled using classical simulators (emulators) of quantum computers and the actual quantum hardware available to us today. The list of problems we tackle includes propagation of a free wave packet, vibration of a harmonic oscillator, and tunneling through a barrier. Each of these problems starts with the initial wave packet setup. Although Qiskit provides a general method for initializing wave functions, in most cases it generates deep quantum circuits. While these circuits perform well on noiseless simulators, they suffer from excessive noise on quantum hardware. To overcome this issue, we designed a shallower quantum circuit for preparing a Gaussian-like initial wave packet, which improves the performance of real hardware. Next, quantum circuits are implemented to apply the kinetic and potential energy operators for the evolution of a wave function over time. The results of our modeling on classical emulators of quantum hardware agree perfectly with the results obtained using the traditional (classical) methods. This serves as a benchmark and demonstrates that the quantum algorithms and Qiskit codes we developed are accurate. However, the results obtained on the actual quantum hardware available today, such as IBM’s superconducting qubits and IonQ’s trapped ions, indicate large discrepancies due to hardware limitations. This work highlights both the potential and challenges of using quantum computers to solve fundamental quantum molecular dynamics problems.

本研究探讨了如何利用当前可用的量子计算机经典模拟器（仿真器）以及实际量子硬件，对量子分子动力学中的基础问题进行建模。本研究涉及的问题包括自由波包传播、简谐振子振动以及势垒隧穿。上述每个问题均以初始波包搭建作为起始步骤。尽管Qiskit提供了通用的波函数初始化方案，但在多数情况下会生成深度较大的量子电路。这类电路在无噪模拟器上表现优异，但在实际量子硬件上却会遭遇严重的噪声干扰。为解决该问题，我们设计了一款深度更浅的量子电路，用于制备类高斯初始波包，从而提升了实际硬件上的运行性能。随后，我们搭建量子电路以实现动能与势能算符，用于实现波函数随时间的演化。我们在量子硬件经典仿真器上得到的建模结果，与传统（经典）方法得到的结果完全一致。该结果可作为基准验证，证明我们开发的量子算法与Qiskit代码具备准确性。然而，在当前可用的实际量子硬件（如IBM的超导量子比特与IonQ的囚禁离子阱设备）上得到的结果却存在显著偏差，这源于硬件本身的局限性。本研究既展现了利用量子计算机解决基础量子分子动力学问题的潜力，也点明了其中存在的挑战。