Quintana C M, Chen Yu, Sank D, Petukhov A G, White T C, Kafri Dvir, Chiaro B, Megrant A, Barends R, Campbell B, Chen Z, Dunsworth A, Fowler A G, Graff R, Jeffrey E, Kelly J, Lucero E, Mutus J Y, Neeley M, Neill C, O'Malley P J J, Roushan P, Shabani A, Smelyanskiy V N, Vainsencher A, Wenner J, Neven H, Martinis John M
Department of Physics, University of California, Santa Barbara, California 93106, USA.
Google Inc., Santa Barbara, California 93117, USA.
Phys Rev Lett. 2017 Feb 3;118(5):057702. doi: 10.1103/PhysRevLett.118.057702. Epub 2017 Jan 31.
By analyzing the dissipative dynamics of a tunable gap flux qubit, we extract both sides of its two-sided environmental flux noise spectral density over a range of frequencies around 2k_{B}T/h≈1 GHz, allowing for the observation of a classical-quantum crossover. Below the crossover point, the symmetric noise component follows a 1/f power law that matches the magnitude of the 1/f noise near 1 Hz. The antisymmetric component displays a 1/T dependence below 100 mK, providing dynamical evidence for a paramagnetic environment. Extrapolating the two-sided spectrum predicts the linewidth and reorganization energy of incoherent resonant tunneling between flux qubit wells.
通过分析可调谐间隙磁通量子比特的耗散动力学，我们在约2k_{B}T/h≈1 GHz的一系列频率范围内提取了其双边环境磁通噪声谱密度的两侧，从而能够观察到经典 - 量子交叉。在交叉点以下，对称噪声分量遵循1/f幂律，该幂律与接近1 Hz的1/f噪声幅度相匹配。反对称分量在100 mK以下呈现1/T依赖性，为顺磁环境提供了动力学证据。对双边谱进行外推可预测磁通量子比特阱之间非相干共振隧穿的线宽和重组能。
