Attosecond angular streaking and tunnelling time in atomic hydrogen
Attosecond angular streaking and tunnelling time in atomic hydrogen
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DOI：
10.1038/s41586-019-1028-3
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发表时间：
2019-04-04
期刊：
影响因子：
64.8
通讯作者：
Litvinyuk, I. V.
中科院分区：
文献类型：
--
作者：
Sainadh, U. Satya;Xu, Han;Litvinyuk, I. V.
粒子穿过势垒的隧道是量子力学的一个关键特征，它涉及波粒二象性的核心。这种现象在经典物理学中没有对应物，并且没有结构良好的动力学可观测值可用于确定“隧道时间”。近年来，随着超快激光器和阿秒计量学的出现，关于隧道量子粒子是否在势垒下度过有限且可测量的时间的争论(1-5)再次被点燃(6)。特别重要的是阿秒角条纹（“attoclock”）技术（7），该技术可以以几阿秒的精度对强场电离中电子的释放进行计时。最初的测量（7-10）证实了隧道效应是瞬时的这一普遍观点，但后来的研究（11,12）涉及多电子原子——无法精确建模，使电离动力学的解释复杂化——声称隧道时间有限。相比之下，氢原子的简单性可以实现精确的实验测量和计算(13-15)，并使其成为方便的基准。在这里，我们报告了原子氢的原子时钟和动量空间成像（16）实验，并将这些结果与基于三维时间相关薛定谔方程和我们的实验激光脉冲参数的精确模拟进行比较。我们发现测量数据和模拟数据之间非常吻合，证实了原子氢原子钟技术的早期理论研究（17）的结论，该研究为瞬时隧道效应提出了令人信服的论据。此外，我们将库仑势确定为电子发射方向和峰值电场方向之间测量角度的唯一原因：该角度已归因于（11,12）有限的隧道时间。我们对任何隧道延迟设置了 1.8 阿秒的上限，这与最近的理论发现 (18) 一致，并排除了将所有常用的“隧道时间”(19) 解释为“电子在势垒下花费的时间”(20)。
The tunnelling of a particle through a potential barrier is a key feature of quantum mechanics that goes to the core of wave-particle duality. The phenomenon has no counterpart in classical physics, and there are no well constructed dynamical observables that could be used to determine 'tunnelling times'. The resulting debate(1-5) about whether a tunnelling quantum particle spends a finite and measurable time under a potential barrier was reignited in recent years by the advent of ultrafast lasers and attosecond metrology(6). Particularly important is the attosecond angular streaking ('attoclock') technique(7), which can time the release of electrons in strong-field ionization with a precision of a few attoseconds. Initial measurements(7-10) confirmed the prevailing view that tunnelling is instantaneous, but later studies(11,12) involving multi-electron atoms-which cannot be accurately modelled, complicating interpretation of the ionization dynamics-claimed evidence for finite tunnelling times. By contrast, the simplicity of the hydrogen atom enables precise experimental measurements and calculations(13-15) and makes it a convenient benchmark. Here we report attoclock and momentum-space imaging(16) experiments on atomic hydrogen and compare these results with accurate simulations based on the three-dimensional time-dependent Schrodinger equation and our experimental laser pulse parameters. We find excellent agreement between measured and simulated data, confirming the conclusions of an earlier theoretical study(17) of the attoclock technique in atomic hydrogen that presented a compelling argument for instantaneous tunnelling. In addition, we identify the Coulomb potential as the sole cause of the measured angle between the directions of electron emission and peak electric field: this angle had been attributed(11,12) to finite tunnelling times. We put an upper limit of 1.8 attoseconds on any tunnelling delay, in agreement with recent theoretical findings(18) and ruling out the interpretation of all commonly used 'tunnelling times'(19) as 'time spent by an electron under the potential barrier'(20).