离子阱系统中电场噪声与声子退相干机制关系的研究

In the development of large-scale ion trap quantum computer, electric field noise is a key factor affecting the stability of trapped ions, reducing the coherence time of quantum state storage, and reducing the fidelity of quantum gate operation. There are many reasons for the electric field noise near the trapped ion qubits, but most of them have not been clearly studied and suppressed. The ion motion state utilizes Coulomb vibration to realize information sharing and controlled operation. Therefore, the research on the electric field noise that affects the phonon quantity change rate (heating rate) and the phonon superposition state phase is the key factor to improve the phonon state preparation and operation fidelity and prolong The key factor of coherence time. In the past studies, the system was described as a linear system, but the experimental results were quite different from the theoretical calculations. Therefore, this proposal will study the relationship between the electric field noise spectrum and the thermal rate and decoherence time. The mathematical model of the system will be established by separating the single spectrum and measuring its response function. Then, by measuring the response of the input combined spectral noise, the sum of the two identical single spectral response functions measured separately is compared to realize the research and measurement of the degree of nonlinearity of the system. In the end, the system's electric field noise mechanism and its effects will be clarified, and efforts will be made to find a corresponding noise cancellation method.

电场噪声在实现大规模离子阱量子计算机的研制过程中是影响囚禁离子稳定性、降低量子态存储相干时间、减少量子门操作保真度等一系列问题的关键因素。囚禁离子量子比特附近的电场噪声产生的原因有多种，但大部分都还没被研究清楚并加以抑制。离子运动态利用库伦振动实现信息共享和受控操作，因此对影响声子数量改变速度（加热率）和声子叠加态相位的电场噪声的研究是提高声子态制备和操作保真度、延长相干时间的关键因素。以往研究中系统描述为线性系统模型，但实验结果与理论计算有很大差距。因此，本课题研究电场噪声频谱与热率及退相干时间的关系，通过分离单一频谱并测量其响应函数的方法建立系统数学模型。再通过测量输入组合频谱噪声的响应，对比分别测量的两相同单一频谱响应函数之和，实现对系统非线性程度的研究与测量。最终，将阐明系统电场噪声机制及其影响，并努力找到对应噪声消除方法。

离子量子比特利用自旋电子态与运动外态共同实现量子计算所需量子比特状态及量子门操作。自旋电子态受外场影响较弱，而利用带电原子间的库伦运动实现信息共享和受控操作的运动外态由于带电，极易受到外电场的影响，导致囚禁离子不稳定、降低量子态存储相干时间、量子门操作保真度降低等一系列问题，特别是随着离子数量增多、器件体积减小而更加严重。囚禁离子附近的电场噪声有多种来源，不同噪声的行为描述、区分溯源、形成机理及抑制方法是领域中的前沿研究问题。以往研究中系统描述模型与实验结果有较大差距，因此本项目围绕对影响声子数量改变速度（加热率）和声子叠加态相位的电场噪声的研究、电场噪声频谱与声子加热率及退相干时间的关系进行研究，拟用于提高声子态制备和操作保真度、延长相干时间等。项目重新设计了微波谐振器关键器件、搭建了囚禁离子与加热率测量实验系统，并取得了一些创新性成果。项目全模型仿真了用于驱动离子囚禁的螺旋形微波谐振器，制作的谐振器无载Q值可以稳定提高到约700，提高了系统滤波和驱动微波噪声抑制能力。搭建了一套宏观刀片式离子囚禁系统，实现了单、双量子态的制备读取与操作、实现了囚禁离子的doppler冷却与运动基态冷却，测量了系统声子加热率。通过对系统电学方面的优化、替换新型高Q谐振器，实现了系统声子加热率的显著降低。证明了项目研究中通过制作高Q谐振器分离单一频率电场噪声对离子加热的影响的假设。项目进行过程中，为提高系统稳定性、重复性和一致性，方便快捷的完成电场噪声的准确测量，还设计加工了标准化的离子阱芯片电极；提出加热率测量时离子-电极距离可调节一致的全电学控制方法。