论文标题
无门态制备,用于快速变化量子本素莫尔模拟:ctrl-vqe
Gate-free state preparation for fast variational quantum eigensolver simulations: ctrl-VQE
论文作者
论文摘要
当前,变异量子本质量(VQE)是解决近期量子计算机上电子结构问题的旗舰算法。该混合量子/经典算法涉及在量子硬件上实现一系列参数化门以生成目标量子状态,然后测量分子hamiltonian的期望值。由于有限的相干时间和频繁的门误差,可以实现的门的数量在当前量子设备上仍然有限,从而阻止了对具有显着纠缠的系统的准确应用,例如密切相关的分子。在这项工作中,我们提出了一种替代算法(我们称为CTRL-VQE),其中用于状态制备的量子电路被完全删除,并由量子控制例程取代,该量子控制例程在变化上塑造了脉冲以将初始的Hartree-Fock状态驱动到完整的CI目标状态。与VQE一样,优化的目标函数是量子映射分子哈密顿量的期望值。但是,通过删除量子电路,可以通过直接优化脉冲来大大降低状态制备所需的相干时间。我们通过直接优化脉冲形状来证明该方法的潜力,该脉冲形状准确地对氢分子(共价键)和氦氢化离子(离子键)(离子键)的解离曲线进行了模拟,我们计算了LIH与四个Transmons的单点能量。
The variational quantum eigensolver (VQE) is currently the flagship algorithm for solving electronic structure problems on near-term quantum computers. This hybrid quantum/classical algorithm involves implementing a sequence of parameterized gates on quantum hardware to generate a target quantum state, and then measuring the expectation value of the molecular Hamiltonian. Due to finite coherence times and frequent gate errors, the number of gates that can be implemented remains limited on current quantum devices, preventing accurate applications to systems with significant entanglement, such as strongly correlated molecules. In this work, we propose an alternative algorithm (which we refer to as ctrl-VQE) where the quantum circuit used for state preparation is removed entirely and replaced by a quantum control routine which variationally shapes a pulse to drive the initial Hartree-Fock state to the full CI target state. As with VQE, the objective function optimized is the expectation value of the qubit-mapped molecular Hamiltonian. However, by removing the quantum circuit, the coherence times required for state preparation can be drastically reduced by directly optimizing the pulses. We demonstrate the potential of this method numerically by directly optimizing pulse shapes which accurately model the dissociation curves of the hydrogen molecule (covalent bond) and helium hydride ion (ionic bond), and we compute the single point energy for LiH with four transmons.