[论文解读] Microwave-based quantum control and coherence protection of tin-vacancy spin qubits in a strain-tuned diamond membrane heterostructure

Xinghan Guo, Alexander M. Stramma+20 more|arXiv (Cornell University)|Jul 21, 2023

Diamond and Carbon-based Materials Research被引用 6

一句话总结

该论文展示了在应变调制的金刚石膜异质结构中，通过微波实现对锡空位（SnV）自旋量子比特的控制及相干性保护。通过将掺杂SnV的金刚石膜与熔融石英键合，被动地产生约0.1%的拉伸应变，实现了高保真度微波控制（99.36%门保真度）和在4 K下长达223(10) μs的自旋相干时间——这是该温度下IV族量子比特的纪录性能。

ABSTRACT

Robust spin-photon interfaces in solids are essential components in quantum networking and sensing technologies. Ideally, these interfaces combine a long-lived spin memory, coherent optical transitions, fast and high-fidelity spin manipulation, and straightforward device integration and scaling. The tin-vacancy center (SnV) in diamond is a promising spin-photon interface with desirable optical and spin properties at 1.7 K. However, the SnV spin lacks efficient microwave control and its spin coherence degrades with higher temperature. In this work, we introduce a new platform that overcomes these challenges - SnV centers in uniformly strained thin diamond membranes. The controlled generation of crystal strain introduces orbital mixing that allows microwave control of the spin state with 99.36(9) % gate fidelity and spin coherence protection beyond a millisecond. Moreover, the presence of crystal strain suppresses temperature dependent dephasing processes, leading to a considerable improvement of the coherence time up to 223(10) $μ$s at 4 K, a widely accessible temperature in common cryogenic systems. Critically, the coherence of optical transitions is unaffected by the elevated temperature, exhibiting nearly lifetime-limited optical linewidths. Combined with the compatibility of diamond membranes with device integration, the demonstrated platform is an ideal spin-photon interface for future quantum technologies.

研究动机与目标

• 解决在较高温度下锡空位（SnV）中心存在高效微波控制不足和自旋相干时间有限的问题。
• 克服在金刚石中实现足够应变（约0.1%）以实现有效自旋-应变相互作用和轨道混成的挑战。
• 开发一种可扩展、可集成的平台，用于在4 K下实现SnV量子比特的高保真度量子控制和长寿命自旋相干性。
• 通过在可及的低温环境（4 K）下运行，无需mK系统，实现实际的量子网络和传感应用。

提出的方法

• 使用高质量化学气相沉积法制造掺杂SnV中心的薄金刚石膜。
• 通过热膨胀系数不匹配的熔融石英基板键合金刚石膜，诱导均匀的面内拉伸应变（约0.1%）。
• 在键合后使用共面波导结构施加微波脉冲，实现自旋的相干操控。
• 采用动力学解耦序列（XY8、2XY8）延长自旋相干时间。
• 通过光致发光光谱测量光学特性，评估零声子线位移和线宽。
• 在1.7 K和4 K下，利用随机基准测试和拉比振荡表征微波门保真度。

Figure 1: Strained SnV in diamond membrane heterostructures. (a) Schematics of the diamond-fused silica heterostructure. The static, tensile strain inside the membrane is generated from the disparity of thermal expansion ratios of diamond and fused silica. (b) The microscope image of the diamond mem

实验结果

研究问题

• RQ1 在金刚石膜中可控应变是否能实现对SnV自旋量子比特的高效微波控制？
• RQ2 在4 K下，应变诱导的轨道混成在多大程度上增强了SnV中心的自旋相干性？
• RQ3 在应变调制的膜平台中，SnV自旋量子比特的相干时间如何随温度变化？
• RQ4 在此应变异质结构中，SnV中心的光学相干性是否能在较高温度（最高7 K）下保持？
• RQ5 该平台是否与微波和光子元件的可扩展集成兼容？

主要发现

• 在4.50(2) MHz频率和24 dBm微波功率下，SnV自旋量子比特的拉比门保真度达到99.36(9)%。
• 在1.7 K下，自旋相干时间（T₂）达到1.57(8) ms；在4 K下，通过动力学解耦实现223(10) μs。
• 在4 K下，T₂,echo为74(2) μs，T₂,2XY8达到去极化限制值223(10) μs。
• 零声子线线宽在高达7 K时仍低于52.0(8) MHz，表明光学相干性接近寿命限制。
• 应变诱导的轨道混成实现了有效的自旋控制，无需外加磁场。
• 该平台可在4 K下运行——与mK系统相比，显著降低了低温基础设施需求。

Figure 2: Optical properties of the strained SnV center under applied magnetic fields at $1.7\text{\,}\mathrm{K}$ . (a) The energy splitting rate between the A1-B2 spin conserving transitions with respect to the polar angle $\theta$ of the applied magnetic field at different azimuthal angle $\phi$ .