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arXiv 1004.1863cond-mat.supr-con
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强驱动约瑟夫森结的量子和经典共振逃逸

Quantum and classical resonant escapes of a strongly-driven Josephson junction

H. F. Yu, X. B. Zhu, Z. H. Peng, W. H. Cao, D. J. Cui, Ye Tian, G. H. Chen, D. N. Zheng, X. N. Jing, Li Lu, S. P. Zhao, Siyuan Han

摘要:

本文研究了直流SQUID在25 mK(远低于量子-经典交叉温度$T_{cr}$)强共振交流驱动下的相位逃逸特性。SQUID包含两个Nb/Al-AlO $_{x} $ /Nb隧道结,其约瑟夫森电感远大于回路电感,因此其可被视为具有可调临界电流的单个结。我们发现,随着微波功率的增加$W$和在一定的频率$ν$和$ν$ /2,在开关电流分布,\textrm{which is the result of macroscopic quantum tunneling of the phase across the junction}的单一主峰,首先向低偏置电流$I$,然后共振峰的发展。这些结果解释了量子共振相位逃逸涉及单光子和双光子微波抑制势垒。随着$W$进一步增加,主峰逐渐消失,并且共振峰增长为单个共振峰,同时进一步向较低的$I$移动。在一定的$W$处,出现第二共振峰,根据$ν$的值,其可以位于非常低的$I$处。基于经典运动方程的分析表明,这种共振峰可能是由于非线性系统的分岔导致相位粒子以极大振幅共振逃逸而产生的。我们的实验结果和理论分析表明,在$T\ll T_{cr}$中,相粒子的逃逸可以由经典过程控制,如强交流驱动下非线性系统的动力学分岔。

英文摘要:

The properties of phase escape in a dc SQUID at 25 mK, which is well below quantum-to-classical crossover temperature $T_{cr}$, in the presence of strong resonant ac driving have been investigated. The SQUID contains two Nb/Al-AlO$_{x} $/Nb tunnel junctions with Josephson inductance much larger than the loop inductance so it can be viewed as a single junction having adjustable critical current. We find that with increasing microwave power $W$ and at certain frequencies $ν$ and $ν$/2, the single primary peak in the switching current distribution, \textrm{which is the result of macroscopic quantum tunneling of the phase across the junction}, first shifts toward lower bias current $I$ and then a resonant peak develops. These results are explained by quantum resonant phase escape involving single and two photons with microwave-suppressed potential barrier. As $W$ further increases, the primary peak gradually disappears and the resonant peak grows into a single one while shifting further to lower $I$. At certain $W$, a second resonant peak appears, which can locate at very low $I$ depending on the value of $ν$. Analysis based on the classical equation of motion shows that such resonant peak can arise from the resonant escape of the phase particle with extremely large oscillation amplitude resulting from bifurcation of the nonlinear system. Our experimental result and theoretical analysis demonstrate that at $T\ll T_{cr}$, escape of the phase particle could be dominated by classical process, such as dynamical bifurcation of nonlinear systems under strong ac driving.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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