在时空极限下追踪电子

摘要(中文译文)

电子波函数的动力学特性往往对其空间分布产生非平凡的影响，例如在隧穿过程或化学键形成过程中。然而，要揭示时空耦合，需要在本征的电子波函数尺度上，即在所谓的时空极限下，进行超快视频成像。本文利用具有阿秒时间分辨率的原子尺度光波驱动扫描隧道显微镜，在电子隧穿能量势垒的过程中，实验上实现了对单个电子在时空极限下本征量子运动的观测。通过两束时间延迟的近红外脉冲形成相位控制的单周期波形来调制隧穿势垒，识别出短于1飞秒的孤立电子隧穿瞬态过程。测量得到的空间延展取决于多光子动力学与场驱动动力学之间的相互作用，这一点已通过完整的量子模拟得到证实。我们实验上将阿秒受限的隧穿波包局域化到埃尺度，并利用其绘制了银表面上单个铜吸附原子的图像。这种将阿秒科学与原子尺度扫描隧道显微镜相融合的方法，使得研究原子、分子和固体内部的波函数动力学成为可能。

Abstract

The dynamics of an electronic wavefunction often have non-trivial consequences on its spatial distribution, for example, during tunnelling or chemical bond formation. Yet, revealing spatio-temporal coupling requires ultrafast videography at the intrinsic size of electronic wavefunctions, at the so-called space-time limit. Here we experimentally access the intrinsic quantum motion of individual electrons at the space-time limit while they are tunnelling through an energy barrier, using atomic-scale lightwave-driven scanning tunnelling microscopy with attosecond time resolution. While modulating the tunnelling barrier with two time-delayed near-infrared pulses forming phase-controlled single-cycle waveforms, isolated electron tunnelling transients shorter than 1 fs are identified. The measured spatial extension depends on the interplay of multi-photon and field-driven dynamics, as confirmed by full quantum simulations. We experimentally localize the attosecond-confined tunnelling wave packet on the angstrom scale and use it to map a single copper adatom on a silver surface. This fusion of attosecond science with atomic-scale scanning tunnelling microscopy makes it possible to study wavefunction dynamics inside atoms, molecules and solids.

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