连续动态解耦估计Laser频率噪声谱
Estimation of the Laser Frequency Nosie Spectrum by Continuous Dynamical Decoupling
摘要：
激光频率噪声引起的退相干是量子信息处理的重要障碍之一。为了抑制这种退相干，噪声功率谱密度需要被精确地表征。特别是，基于量子比特相干特性的噪声谱测量将是一种有意义且仍然具有挑战性的方法。本文基于连续动态解耦技术，对激光频率噪声谱进行了理论分析和实验研究。我们首先估计的混合噪声（包括激光和磁噪声）频谱高达$(2π)$ 530 kHz的监测从初始状态$+X$的横向弛豫，然后由梯度下降的数据处理协议。然后通过将量子比特编码在不同的塞曼子能级上，提取激光噪声的贡献。我们还通过将这些噪声与假定线宽可忽略不计的驱动激光进行类比，研究了两个足够强的噪声分量。实验验证了该方法的有效性，并对噪声进行了表征。
英文摘要：
Decoherence induced by the laser frequency noise is one of the most important obstacles in the quantum information processing. In order to suppress this decoherence, the noise power spectral density needs to be accurately characterized. In particular, the noise spectrum measurement based on the coherence characteristics of qubits would be a meaningful and still challenging method. Here, we theoretically analyze and experimentally obtain the spectrum of laser frequency noise based on the continuous dynamical decoupling technique. We first estimate the mixture-noise (including laser and magnetic noises) spectrum up to $(2π)$530 kHz by monitoring the transverse relaxation from an initial state $+X$, followed by a gradient descent data process protocol. Then the contribution from the laser noise is extracted by enconding the qubits on different Zeeman sublevels. We also investigate two sufficiently strong noise components by making an analogy between these noises and driving lasers whose linewidth assumed to be negligible. This method is verified experimentally and finally helps to characterize the noise.
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