Quantum entanglement is one of the most mysterious and fastest phenomena in nature. Scientists at TU Wien (Vienna), in collaboration with research teams from China, have taken a deep dive into this ultrafast process. Using advanced computer simulations, they have successfully analyzed how entanglement emerges on an attosecond scale—an almost unimaginable fraction of a second. Their groundbreaking findings, published in Physical Review Letters, offer new insights into the very fabric of quantum physics.
Entanglement: More Than Just a Connection
In the quantum world, two entangled particles are not just linked—they essentially become a single entity. Their properties are no longer independent but intertwined, even if they are separated by vast distances. “You could say that the particles do not have individual properties; they only have shared properties,” explains Prof. Joachim Burgdörfer from TU Wien’s Institute of Theoretical Physics. “Mathematically, they belong together, no matter how far apart they are.”
Most research on entanglement focuses on maintaining it for as long as possible, especially for applications like quantum cryptography and quantum computing. However, Prof. Iva Březinová and her team had a different goal: to understand how entanglement emerges in the first place and what physical mechanisms drive this process on incredibly short time scales.
A Laser Pulse and the Birth of Entanglement
The study examined what happens when an atom is struck by an intense, high-frequency laser pulse. This interaction rips one electron out of the atom, sending it flying away. But if the laser is strong enough, a second electron is also affected—it absorbs energy and shifts to a higher orbital around the nucleus.
At this point, quantum entanglement comes into play. “We can show that these two electrons are now entangled,” says Burgdörfer. “To describe them, you must analyze them as a pair. Measuring one provides information about the other—no matter the distance between them.”
The Electron That Doesn’t Know When It Left
The team discovered something even more astonishing: the moment an electron leaves the atom is fundamentally uncertain. By using a combination of two laser beams in their simulations, they found that the ‘birth time’ of the free electron is entangled with the state of the electron that remains behind.
“The electron itself doesn’t know when it was ‘born,’” says Burgdörfer. “It exists in a quantum superposition of different states, meaning it both left earlier and later at the same time.”
This concept defies classical logic—there is no definitive moment in time when the electron escapes. However, the uncertainty is not random. The timing is linked to the energy state of the remaining electron. If the second electron is in a higher energy state, the first electron was more likely ejected earlier. If the remaining electron has lower energy, the escaping electron likely left later. On average, this time difference is around 232 attoseconds—a billionth of a billionth of a second.
Measuring the Unimaginable
While these time differences seem impossibly short, they are not just theoretical. Scientists believe they can be measured experimentally. “We are already in discussions with research teams interested in confirming this ultrafast entanglement,” says Burgdörfer.
Rethinking Instantaneous Events
This research challenges the idea that quantum effects happen instantaneously. Even the simplest quantum events have an internal temporal structure that unfolds over attoseconds.
“The electron doesn’t simply jump out of the atom—it behaves more like a wave spilling out,” says Březinová. “This wave-like process takes time, and it is during this phase that quantum entanglement emerges. By capturing these details, we gain a clearer picture of quantum mechanics at its most fundamental level.”
This discovery marks an important step toward unraveling the secrets of quantum physics. As scientists refine their ability to measure these ultrafast interactions, we may soon have an even deeper understanding of how quantum reality operates at the smallest and fastest scales imaginable.
