Department of Nuclear Science and Engineering, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts 02139, USA.
Nat Commun. 2013;4:2337. doi: 10.1038/ncomms3337.
Gate operations in a quantum information processor are generally realized by tailoring specific periods of free and driven evolution of a quantum system. Unwanted environmental noise, which may in principle be distinct during these two periods, acts to decohere the system and increase the gate error rate. Although there has been significant progress characterizing noise processes during free evolution, the corresponding driven-evolution case is more challenging as the noise being probed is also extant during the characterization protocol. Here we demonstrate the noise spectroscopy (0.1-200 MHz) of a superconducting flux qubit during driven evolution by using a robust spin-locking pulse sequence to measure relaxation (T(1ρ)) in the rotating frame. In the case of flux noise, we resolve spectral features due to coherent fluctuators, and further identify a signature of the 1 MHz defect in a time-domain spin-echo experiment. The driven-evolution noise spectroscopy complements free-evolution methods, enabling the means to characterize and distinguish various noise processes relevant for universal quantum control.
在量子信息处理器中，门操作通常通过对量子系统的特定自由和驱动演化周期进行定制来实现。在这两个周期中，可能存在不同的不需要的环境噪声，这些噪声会使系统退相干并增加门错误率。尽管在自由演化期间对噪声过程进行特征描述已经取得了重大进展，但由于在特征描述协议期间也存在被探测的噪声，因此相应的驱动演化情况更具挑战性。在这里，我们通过使用强大的自旋锁定脉冲序列来测量旋转框架中的弛豫（T(1ρ))，演示了超导磁通量子位在驱动演化期间的噪声光谱（0.1-200 MHz）。对于通量噪声，我们解析了由于相干波动器引起的光谱特征，并在时域自旋回波实验中进一步确定了 1 MHz 缺陷的特征。驱动演化噪声光谱补充了自由演化方法，为特征描述和区分与通用量子控制相关的各种噪声过程提供了手段。
