近日，美国科罗拉多大学的William K. Schenken及其研究团队取得一项新进展。经过不懈努力，他们揭示了强相互作用自旋综中的长寿期相干性质。相关研究成果已于2024年9月12日在国际知名学术期刊《物理评论A》上发表。

该研究团队探讨了如何利用类似Carr-Purcell-Meiboom-Gill（CPMG）的简单脉冲序列来增强大量自旋量子比特的相干性，并将其作为一种重要的表征工具。研究人员在金刚石中高密度氮空穴（NV）中心集合上实施了周期性驱动，并研究了脉冲旋转偏移作为控制参数对动力学的影响。

研究人员使用了一个包含多个NV密度不同区域的单一金刚石样品，这些区域的不同导致了NV-NV偶极相互作用强度的变化。出乎意料的是，他们发现CPMG序列中偏离理想脉冲的旋转偏移（通常被视为脉冲误差），在保持沿脉冲设定轴的相干性方面起着关键作用，即便是在名义上零旋转偏移的情况下也是如此。

相干性得以保持的原因在于产生了一个有效场，该场在小偏移范围内与旋转偏移的大小呈线性关系。除了延长相干时间外，他们还通过比较旋转偏移依赖的相干性与数值模拟结果，测量了哈密顿量中的无序和偶极贡献，从而定量提取了金刚石内部构成自旋组分的密度。

据悉，周期性驱动已成为控制、设计和表征多体量子系统的有力工具。然而，所需的脉冲序列往往复杂冗长，或需具备控制各个自由度的能力。

附：英文原文

Title: Long-lived coherences in strongly interacting spin ensembles

Author: William K. Schenken, Simon A. Meynell, Francisco Machado, Bingtian Ye, Claire A. McLellan, Maxime Joos, V. V. Dobrovitski, Norman Y. Yao, Ania C. Bleszynski Jayich

Issue&Volume: 2024/09/12

Abstract: Periodic driving has emerged as a powerful tool to control, engineer, and characterize many-body quantum systems. However, the required pulse sequences are often complex, long, or require the ability to control the individual degrees of freedom. In this work, we study how a simple Carr-Purcell–Meiboom-Gill (CPMG)-like pulse sequence can be leveraged to enhance the coherence of a large ensemble of spin qubits and serve as an important characterization tool. We implement the periodic drive on an ensemble of dense nitrogen-vacancy (NV) centers in diamond and examine the effect of pulse rotation offset as a control parameter on the dynamics. We use a single diamond sample prepared with several spots of varying NV density, which, in turn, varies the NV-NV dipolar interaction strength. Counterintuitively, we find that rotation offsets deviating from the ideal pulse in the CPMG sequence (often classified as pulse errors) play a critical role in preserving coherence along an axis set by the pulses even at nominally zero rotation offset. The cause of the coherence preservation is an emergent effective field that scales linearly with the magnitude of the rotation offset for small offsets. In addition to extending coherence, we compare the rotation offset dependence of coherence to numerical simulations to measure the disorder and dipolar contributions to the Hamiltonian to quantitatively extract the densities of the constituent spin species within the diamond.

DOI: 10.1103/PhysRevA.110.032612

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.032612

来源：科学网 小柯机器人