EPFL News
The idea of time in the quantum world has been one of physics’ most difficult conundrums for many years. The precise time of a quantum transition, like an electron tunneling over a barrier, has proven to be infamously challenging to determine, despite the fact that basic quantum mechanics can predict the likelihood of an event occurring. A team of researchers at the École Polytechnique Fédérale de Lausanne (EPFL) has now created a ground-breaking technique to measure these incredibly quick occurrences, demonstrating that the material’s symmetry and shape determine the “speed” of quantum tunneling.
The research represents a dramatic change in how scientists view the subatomic realm and was published in the journal Newton. By employing the intrinsic characteristics of electrons as a “clock,” the scientists have managed to avoid the interference problems that typically impede high-precision quantum measurements.
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The Challenge of Attosecond Timing
Tunneling and photon absorption are examples of quantum events that occur at rates that are incomprehensible to humans. These occurrences frequently take place in quintillionths of a second, or tens of attoseconds (10−18 seconds). To put this into perspective, consider that in the time it takes for these transformations to take place, light cannot even pass through the width of a single virus.
The observer effect has been the main obstacle to quantifying these intervals, according to Hugo Dil, a professor and physicist at EPFL. “Measuring time intervals of this magnitude is notoriously challenging,” says Dil, “particularly because any external timing device can interfere with the very phenomenon one aims to observe” . Humans may access these short periods, as the 2023 Nobel Prize in Physics showed, but using an external reference frequently runs the danger of introducing “artefacts” or inaccuracies in the data.
The “Spin Clock” Solution
SPERS, a sophisticated approach, was used by EPFL to solve this. Intense synchrotron light excites electrons and forces them to leave a substance.
These electrons convey particular information stored in their quantum spin as they are expelled. A superposition of several interfering quantum pathways is produced when light interacts with the electron. Because of this interference, the electron’s spin develops a unique pattern that changes according to how the underlying quantum process develops.
Without the use of an external clock, the researchers were able to determine the length of the transition by examining these subtle variations in spin patterns in relation to the electron’s energy. This internal “spin clock” offers a clear view of how the electron’s wavefunction changes from its initial condition to a higher order of energy.
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Symmetry and the Speed of Quantum Leaps
The study’s most startling finding is that the length of these quantum events varies greatly depending on the material’s atomic-level “shape” or symmetry.
A number of materials with different geometries were investigated by the researchers:
- 3D Copper: The quantum transition in this typical, highly symmetric three-dimensional structure happened quite quickly, taking about 26 attoseconds to complete.
- Bilayer Materials (TiSe2 and TiTe2): These materials behave more like flat sheets and are made up of loosely connected layers. In this case, the operation took 140–175 attoseconds, a substantial slowdown.
- Chain-like Copper Telluride (CuTe): This substance has a straightforward, one-dimensional chain structure. Its transition time exceeded 200 attoseconds in this low-symmetry setting.
The pattern was obvious: the longer the quantum transition lasted, the simpler and more reduced the material’s structure. In essence, lower symmetry “slows down” the quantum leap.
Future Implications
This discovery offers important new understandings of whether quantum transitions are indeed instantaneous or always have a defined period. Understanding these timelines has useful implications for future technological advancements that go beyond theoretical physics.
“Understanding the duration of a quantum transition can assist researchers in creating materials with targeted quantum characteristics,” the investigators stated. This degree of accuracy is necessary to advance future technologies like high-speed electronics and quantum computing that depend on precise manipulation of quantum states.
The EPFL team has opened the door to a better comprehension of the function of time in the subatomic realm by revealing the connection between material symmetry and quantum timing.
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