频率梳NMR谱探测量子点核自旋浴中的短秒关联时间
Few-second-long correlation times in a quantum dot nuclear spin bath probed by frequency-comb NMR spectroscopy
摘要：
光谱学中的一个关键挑战是不均匀加宽，它掩盖了均匀的光谱线型和潜在的相干动力学。在光谱学中使用了多种技术，包括四波混频和光谱烧孔，而在核磁共振（NMR）中，自旋回波是抵消不均匀性的最常用方法。然而，自旋回波和其他序列中使用的高功率脉冲经常产生虚假的动力学，掩盖了在量子信息应用中起关键作用的微妙的自旋相关性。在这里，我们开发的NMR技术，使相关时间的波动，在一个核自旋池的个别量子点进行探测。这是通过使用频率梳激励来实现的，频率梳激励允许测量均匀的NMR线形，避免了高功率脉冲。我们发现核自旋相关时间超过1秒的自组装InGaAs量子点-四个数量级以上的无应变III-V族半导体。观察到的核自旋涨落的冻结为设计具有良好理解的、高度稳定的核自旋浴的量子点自旋量子比特开辟了道路。
英文摘要：
One of the key challenges in spectroscopy is inhomogeneous broadening that masks the homogeneous spectral lineshape and the underlying coherent dynamics. A variety of techniques including four-wave mixing and spectral hole-burning are used in optical spectroscopy while in nuclear magnetic resonance (NMR) spin-echo is the most common way to counteract inhomogeneity. However, the high-power pulses used in spin-echo and other sequences often create spurious dynamics obscuring the subtle spin correlations that play a crucial role in quantum information applications. Here we develop NMR techniques that allow the correlation times of the fluctuations in a nuclear spin bath of individual quantum dots to be probed. This is achieved with the use of frequency comb excitation which allows the homogeneous NMR lineshapes to be measured avoiding high-power pulses. We find nuclear spin correlation times exceeding 1 s in self-assembled InGaAs quantum dots - four orders of magnitude longer than in strain-free III-V semiconductors. The observed freezing of the nuclear spin fluctuations opens the way for the design of quantum dot spin qubits with a well-understood, highly stable nuclear spin bath.
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