Molecular Optimization for Nuclear Spin State Control via a Single Electron Spin Qubit by Optimal Microwave Pulses: Quantum Control of Molecular Spin Qubits
Molecular Optimization for Nuclear Spin State Control via a Single Electron Spin Qubit by Optimal Microwave Pulses: Quantum Control of Molecular Spin Qubits
复制标题
通过最佳微波脉冲通过单电子自旋量子位控制核自旋状态的分子优化：分子自旋量子位的量子控制
DOI：
10.1007/s00723-021-01392-5
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发表时间：
2022
影响因子：
1
通讯作者：
Takui Takeji
中科院分区：
文献类型：
--
作者：
Shibata Taiki;Yamamoto Satoru;Nakazawa Shigeaki;Lapasar Elham Hosseini;Sugisaki Kenji;Maruyama Koji;Toyota Kazuo;Shiomi Daisuke;Sato Kazunobu;Takui Takeji
量子态控制是先进量子技术、新兴量子控制论及其相关领域中最重要的概念之一。分子开壳层实体可以成为实现量子控制技术的试验场，使我们能够操纵分子自旋量子比特（分子自旋量子比特）。在由未成对电子和核自旋组成的精心设计的分子自旋中，电子和核自旋可以分别是总线和客户端量子位。完全控制分子自旋量子位，其中客户端自旋通过超精细耦合相互作用，是实现量子计算机（QC）的关键问题。在固态QC中，有两种方法来控制核客户端量子比特，即通过无线电波（RF）脉冲直接控制核自旋和通过施加到电子自旋量子比特的微波脉冲经由超精细相互作用间接控制。虽然后者在文献中不太受欢迎，但间接性的优点是大大减少了量子比特系统与其环境之间不必要的相互作用。在这项工作中，我们研究分子自旋优化，以找到最佳的实验条件，可以提供实现量子门的高保真度的间接控制方案。在目前的量子系统中，一个电子直接由脉冲ESR技术控制，而不操纵单个超精细共振，但两个核客户自旋的状态通过超精细相互作用间接操纵。选择马来酸氢钾（KHM）自由基和13 C标记的丙二酰自由基单晶作为典型的分子自旋量子比特，说明了超精细张量对称性及其共线性质的重要性。我们发现，超精细耦合张量主轴的非共线性和核自旋之间的非可分辨性/非等价性是极大地降低门保真度的关键问题。
Quantum state control is one of the most important concepts in advanced quantum technology, emerging quantum cybernetics and related fields. Molecular open shell entities can be a testing ground for implementing quantum control technology enabling us to manipulate molecular spin quantum bits (molecular spin qubits). In well-designed molecular spins consisting of unpaired electron and nuclear spins, the electrons and nuclear spins can be bus and client qubits, respectively. Full control of molecular spin qubits, in which client spins interact via hyperfine coupling, is a key issue for implementing quantum computers (QCs). In solid-state QCs, there are two approaches to the control of nuclear client qubits, namely, direct control of nuclear spins by radio-wave (RF) pulses and indirect control via hyperfine interactions by microwave pulses applied to electron spin qubits. Although the latter is less popular in the literature, the indirectness has advantage of greatly reducing unnecessary interactions between a qubit system and its environment. In this work, we investigate molecular spin optimization to find optimal experimental conditions which can afford to achieve the high fidelity of quantum gates by the indirect control scheme. In the present quantum systems, one electron is directly controlled by pulsed ESR techniques without manipulating individual hyperfine resonance, but the states of two nuclear client spins are indirectly steered via hyperfine interactions. Single crystals of potassium hydrogen maleate (KHM) radical and13C-labeled malonyl radical are chosen as typical molecular spin qubits which exemplify the importance of the symmetry of hyperfine tensors and their collinear properties. We have found that both the non-collinearity of the principal axes of hyperfine coupling tensors and the non-distinguishability/non-equivalency between nuclear spins are key issues which extremely reduce the gate fidelity.