In a Regensburg laboratory, laser pulses drive electrons across a gap narrower than a few atoms, and from the resulting current a team has shown what physicists long suspected: an electron cannot be located in space and timed in motion with unlimited precision at once. The finding, a space-time limit distinct from Heisenberg's principle, belongs to a longer human effort to follow matter at ever smaller and faster scales, from the first tracking of a single molecule a decade ago to today's glimpse of electrons at the attosecond. Its promise lies less in what it already delivers than in the grou
Electron Position and Timing Face a Hidden Space-Time Limit, Researchers Show
Pin down when an electron moves, and its wave spreads through space
Mark
So what exactly did they show that was new?
Mimi
That an electron's position and the timing of its motion can't both be fixed with unlimited precision. They observed this experimentally, a limit scientists had only suspected before.
Luke
Worth saying it's not the Heisenberg principle restated. The source is explicit that Heisenberg doesn't impose the same restriction on position and time.
Mark
How does the tradeoff actually work?
Mimi
Pin down the timing more tightly and you have to supply more energy, which makes the electron's wave packet spread out more in space. Co-author Raffael Spachtholz put it that way.
Mark
And the 500-attosecond lag?
Mimi
Simulations from Angel Rubio's team matched the experiment and found the electrons trailed the light field by about 500 attoseconds.
Luke
That figure comes from the simulations reproducing the data, so I'd call it a model-backed result rather than a directly stated measurement.
Mark
What about the promise of electronics hundreds of thousands of times faster than CMOS?
Luke
That's Rupert Huber describing a long-term possibility. The source says plainly it hasn't been demonstrated in these experiments.
Mimi
The nearer goal is chemistry: using tightly confined wave packets, with peak current density up to 1 trillion amperes per square centimeter, to trigger and watch bond changes.
Luke
Same caution there. That's what Repp says they want to do, not what they've done.
Le Pouls
- Electrons refuse to be pinned down in both place and moment at once, and the refusal has now been measured directly for the first time.
- Tightening the timing of an electron's motion forces it to spread across space, so every gain in one sharpness costs the other.
- The researchers built a finer laser system and fired paired light pulses to catch electrons tunneling through a barrier they should not be able to cross.
- Simulations reveal the electrons trailing the light field by about 500 attoseconds, while the experiment is still a foundation rather than a finished application.
In a Regensburg laboratory, laser pulses drive electrons across a gap narrower than a few atoms, and from the resulting current a team has shown what physicists long suspected: an electron cannot be located in space and timed in motion with unlimited precision at once. The finding, a space-time limit distinct from Heisenberg's principle, belongs to a longer human effort to follow matter at ever smaller and faster scales, from the first tracking of a single molecule a decade ago to today's glimpse of electrons at the attosecond. Its promise lies less in what it already delivers than in the groundwork it lays, a way to understand how the timing of electron motion reshapes the spatial life of quantum waves.
In a laboratory in Regensburg, pulses of laser light push electrons off a sharp metal tip and across a gap only a few atomic diameters wide toward a silver surface. The researchers read the electrical current that follows, and from it they have shown something physicists had mostly suspected: an electron's position and the timing of its motion cannot both be fixed with unlimited precision. This space-time limit is distinct from Heisenberg's uncertainty principle, and the work is the product of an international collaboration spanning the Regensburg Center for Ultrafast Nanoscopy and the Max Planck Institute in Hamburg.
The scales are difficult to hold in the mind. Electrons here move about a thousand times faster than atoms and molecules, and key changes unfold over attoseconds, a billionth of a billionth of a second. To meet this challenge, the team built a new laser system with much finer time resolution, using two light pulses separated by a precisely controlled interval to observe how electrons respond. The electrons behave as quantum waves that tunnel through a barrier classical physics says they lack the energy to cross, and the measurement works like a high-speed camera for those wave packets.
Theory and experiment met closely. Simulations showed that electrons lag the light field by about 500 attoseconds, and that the laser pulses carry features of both waves and photons, a mix essential near the limit. The tradeoff became clear: the more precisely an electron is timed, the more energy it needs and the wider its wave packet spreads. A single atom placed on the surface held the packets in a tiny region, allowing microscopy with atomic spatial resolution and attosecond time resolution.
The researchers imagine uses in chemistry, where a single electron transferred to a molecule could, if tightly confined, reach extraordinary local current densities and help trigger and watch bonds break. Faster electronics operating near the intrinsic speed limit of electron motion is another hope. Both remain long-term goals. What the work offers now is a foundation and a systematic way to understand how changes in electron motion reshape the spatial structure of quantum wave functions.
In a laboratory in Regensburg, pulses of laser light push electrons off an extremely sharp metal tip and across a gap of only a few atomic diameters to a silver surface. The researchers watch the electrical current that results. From that current, they have now shown something physicists had mostly suspected: an electron's position and the timing of its motion cannot both be pinned down with unlimited precision.
The finding is called the space-time limit. It is distinct from Heisenberg's uncertainty principle, which does not impose the same kind of restriction on position and time. The work comes from an international collaboration. It includes groups at the Regensburg Center for Ultrafast Nanoscopy, led by Jascha Repp, Rupert Huber, Franz Giessibl and Klaus Richter, and a team at the Max Planck Institute in Hamburg led by Angel Rubio.
The scales involved are hard to hold in the mind. At these distances electrons move roughly a thousand times faster than atoms and molecules, and important changes unfold over attoseconds, one-billionth of a billionth of a second. An atom is about ten million times smaller than a millimeter. The gap between an attosecond and a second is comparable to the gap between a second and the age of the universe. About ten years ago, the Regensburg group used ultrafast scanning tunneling microscopy to follow a single molecule through space and time for the first time. Following individual electrons is a harder problem.
For this experiment the team built a new laser system with much finer time resolution than earlier setups. To learn when the electrons move, they used two light pulses separated by a precisely controlled interval. Lead author Simon Maier said that by varying the interval between the pulses, the team can directly observe how the electrons respond. The result was clear evidence of electron motion on attosecond timescales.
The electrons travel as quantum waves rather than as conventional particles. They tunnel through an energy barrier between tip and surface that classical physics says they lack the energy to cross. Doctoral student Katharina Glöckl, a co-author, described the measurement as a high-speed camera for electron wave packets, because it shows at what moment tunneling happens.
Rubio's group ran quantum simulations of the electrons near the space-time limit. These closely matched the experiment and added a detail: the electrons did not respond to the light field instantly but lagged behind it by about 500 attoseconds. The simulations also showed that the laser pulses could not be described purely as waves or purely as photons. Their effects carried features of both, and that mix was essential for working this close to the limit.
The tradeoff itself came into focus through the relationship between timing and the spatial spread of the wave packets. Co-author Raffael Spachtholz explained that the more precisely the electron is pinned down in time, the more energy must be supplied, and the more its wave packet spreads out in space. To test this, the team placed a single atom on the surface to confine the wave packets to a tiny region just before the pulses arrived. Even with substantial energy from the lasers, the packets stayed localized enough for microscopy with atomic spatial resolution and attosecond time resolution.
The researchers see possible uses in chemistry. Transferring one electron to a molecule is the smallest possible transfer of charge, but if that electron is confined to a very small region of space and time, the local peak current density can reach as much as 1 trillion amperes per square centimeter. Repp said the group wants to use such wave packets to trigger chemical reactions and watch, on the relevant scales, how bonds break or change. Huber added that the insights might eventually help run electronics and quantum information processing at the intrinsic speed limit of electron motion, hundreds of thousands of times faster than current CMOS technology.
That last prospect is a long-term goal, not something the current experiments demonstrated. What the work provides is a foundation, and a way to study systematically how changes in electron motion over time reshape the spatial structure of quantum wave functions.
Citations marquantes
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 wave packet spreads out more spatially.— Raffael Spachtholz, co-author
In the long term, the insights could help run electronics and quantum information processing at the intrinsic speed limit of electron motion, hundreds of thousands of times faster than CMOS.— Prof. Rupert Huber
Envie de l'histoire complète ?
Lire l'original sur Science Daily ↗
Science & Space