Amazing stuff! Very impressive! This could be a breakthrough!
"... developed subfemtosecond scanning tunneling microscopy to directly visualize the quantum motion of individual electrons at this space-time limit as they tunneled through an energy barrier.
Modulating the barrier with the carrier field of near-infrared waveforms produced isolated sub–1-femtosecond electronic wave packets, the spatial extent of which depended on a complex interplay between multiphoton and field-driven dynamics. By balancing quantum path interference, the authors minimized the wave function’s space-time volume down to the attosecond-angstrom scale."
"... Between position and time, however, there is no Heisenberg uncertainty principle. A research team ... has now observed for the first time that the location and time evolution of an electron cannot be measured with arbitrary precision simultaneously. This so-called space-time limit has important implications for future applications. ...
ultrafast microscopes are developed and used to directly capture the motion of electrons, atoms, and molecules in microscopic slow-motion movies with the highest possible spatial and temporal resolution.
Ten years ago ... the motion of a single molecule in space and time was resolved for the first time using ultrafast scanning tunneling microscopy.
Compared to atoms and molecules, on this length scale electrons move a thousand times faster—namely, on time scales of attoseconds. ...
To achieve a corresponding increase in temporal resolution compared to previous experiments and to directly image and control the quantum dynamics of individual electrons, the researchers developed a new laser system.
Using its laser pulses they control electron motion on these extreme time scales in such a way that the electrons transfer from an atomically sharp metal tip to a silver surface over a distance of only a few atomic diameters. These electron movements are measured as current, and the temporal information is obtained by using two pulses of light. ...
The electron motion observed in this way exhibits signatures on attosecond timescales—which means that the light pulses can transfer electrons on these timescales, and one can watch them do so.
What makes this special is that the electrons do not move like classical particles. Rather, as quantum mechanical waves, the electrons penetrate the energy barrier between the tip and the sample, for which they actually do not possess enough energy according to the laws of classical physics. They “tunnel” through it, as if they were passing through a massive wall without destroying it. ...
To gain a better understanding of microscopic electron dynamics at the “space-time limit,” ... conducted complex quantum simulations. The calculations explain the experimental results with remarkable accuracy. They also show that the electron does not follow the light field immediately, but with a tiny delay of 500 attoseconds. ...
In this frontier region of the smallest spatial and temporal scales, the fundamental physical limits of quantum physics become apparent on multiple levels. The effect of the laser pulses, for example, cannot be clearly assigned to either the wave or photon picture of light, but bears features of both—and this is precisely what enabled the researchers to penetrate so deeply into the “space-time limit.” When electrons are moved by light pulses on such short time scales, this has complex consequences for the spatial distribution of the electrons, which are described in quantum mechanics as wave packets.
“The more precisely we want to pin down the electron’s position in time, the more energy we need to provide. And as a result, the electron wave packet spreads out more spatially.” The team investigated this relationship using a single atom placed on the surface to confine the electron wave packets atomically just before the light pulses arrive. This allowed them to directly determine the relationship between the spatial and temporal spread of the electron wave packets. Fortunately, despite strong excitation, the electron wave packets remain spatially defined with sufficient sharpness to enable atomically resolved microscopy on attosecond timescales.
With this latest breakthrough, the team is pushing the boundaries of a previously only vaguely suspected spatiotemporal limit of quantum mechanical electron wave functions, in order to systematically investigate for the first time how the temporal dynamics of electrons shape the spatial structure of their wave function. This also opens up entirely new possibilities for applications. For example, transferring an electron to a molecule corresponds to the smallest possible charge transfer; however, if the electron is confined to a tiny space-time volume, this corresponds to extremely high local peak current densities of up to 1 trillion amperes per square centimeter."
From the 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."
In Other Journals | Science
Microscopy at the Space-Time Limit (original news release) "Ultrafast scanning tunneling microscopy at the Regensburg Center for Ultrafast Nanoscopy (RUN) reaches the quantum mechanical space-time limit for the first time"
Fig. 1: Attosecond lightwave STM [scanning tunneling microscopy].
Fig. 2: Evolution of lightwave-driven tunnelling currents with [tau] delay time
Fig. 4: Atomically resolved subcycle currents.
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