Measurement of the spin temperature of optically cooled nuclei and GaAs hyperfine constants in GaAs/AlGaAs quantum dots
Measurement of the spin temperature of optically cooled nuclei and GaAs hyperfine constants in GaAs/AlGaAs quantum dots
复制标题
DOI：
10.1038/nmat4959
复制
发表时间：
2017-10-01
期刊：
影响因子：
41.2
通讯作者：
Skolnick, M. S.
中科院分区：
文献类型：
--
作者：
Chekhovich, E. A.;Ulhaq, A.;Skolnick, M. S.
电子和核自旋的深度冷却相当于实现接近100%的偏振度，并且是固态量子信息技术的关键要求（1-7）。虽然金刚石（2）和SiC（参考文献3）中的单个核自旋的极化达到99%或更高，但量子点（8-10）中的核的极化被限制在50-65%。理论模型将这种限制归因于相干“暗”核自旋态的形成（11-13），但缺乏实验验证，特别是由于偏振度测量的准确性差。在这里，我们测量GaAs/AlGaAs量子点的核极化与高精度使用一种新的方法，使操纵核自旋状态的射频脉冲。偏振度高达80%，这是迄今为止量子点光学冷却的最高记录。该值仍然不受核相干效应的限制。相反，我们发现光学冷却的核在经典的自旋温度框架内得到了很好的描述（14）。我们的研究结果为量子点电子自旋量子比特的进一步发展开辟了一条道路，其中介观核自旋系综的深度冷却用于实现长量子比特相干性（4，5）。此外，GaAs超精细材料常数在这里首次实验测量。
Deep cooling of electron and nuclear spins is equivalent to achieving polarization degrees close to 100% and is a key requirement in solid-state quantum information technologies(1-7). While polarization of individual nuclear spins in diamond(2) and SiC (ref. 3) reaches 99% and beyond, it has been limited to 50-65% for the nuclei in quantum dots(8-10). Theoretical models have attributed this limit to formation of coherent 'dark' nuclear spin states(11-13) but experimental verification is lacking, especially due to the poor accuracy of polarization degree measurements. Here we measure the nuclear polarization in GaAs/AlGaAs quantum dots with high accuracy using a new approach enabled by manipulation of the nuclear spin states with radiofrequency pulses. Polarizations up to 80% are observed-the highest reported so far for optical cooling in quantum dots. This value is still not limited by nuclear coherence effects. Instead we find that optically cooled nuclei are well described within a classical spin temperature framework(14). Our findings unlock a route for further progress towards quantum dot electron spin qubits where deep cooling of the mesoscopic nuclear spin ensemble is used to achieve long qubit coherence(4,5). Moreover, GaAs hyperfine material constants are measured here experimentally for the first time.