A short laser pulse can ionize a helium atom and change the quantum state of the remaining electron.
When a quantum system changes its state, this is called a quantum jump. Usually, these quantum jumps are considered to be instantaneous. Now, new methods for high-precision measurements allow us to study the time evolution of these quantum jumps. On a time scale of attoseconds, there time structure becomes visible. It is he most accurate time measurement of quantum jumps to date. Quantum particles can change their state very quickly, ie “quantum jump”. An atom, for example, can absorb a photon, thereby changing into a state of higher energy. With new methods, developed at TU Wien (Vienna), it is now possible to study the time structure of such extremely fast state changes. Ultrashort laser pulses allow us to analyse temporal structures which used to be inaccessible.
A neutral helium atom has 2 electrons. When it is hit by a high energy laser pulse, it can be ionized: one of the electrons is ripped out of the atom and departs from it. This occurs in attoseconds (billionth of a billionth of a second). “One could imagine that the other electron, which stays in the atom, does not really play an important part in this process—but that’s not true”, says Renate Pazourek (TU Wien). The 2 electrons are correlated, they are closely connected by the laws of quantum physics, they cannot be seen as independent particles. “When one electron is removed from the atom, some of the laser energy can be transferred to the second electron. It remains in the atom, but it is lifted up to a state of higher energy”, says Stefan Nagele.
Stefan Nagele, Joachim Burgdörfer and Renate Pazourek
Thus, it is possible to distinguish between 2 different ionization processes: one, in which the remaining electron gains additional energy and one remains in a state of minimal energy. Using a sophisticated experimental setup, it was possible to show the duration of the 2 processes is not exactly the same. “When the remaining electron jumps to an excited state, the photo ionization process is slightly faster – by about 5 attoseconds”, says Nagele. It is remarkable how well the experimental results agree with theoretical calculations and large-scale computer simulations carried out at the Vienna Scientific Cluster, Austria’s largest supercomputer: “The precision of the experiment is better than 1 attosecond. This is the most accurate time measurement of a quantum jump to date”, says Renate Pazourek.
The experiment provides new insights into the physics of ultrashort time scales. Effects, which a few decades ago were still considered “instantaneous” can now be seen as temporal developments which can be calculated, measured and even controlled. This does not only help to understand the basic laws of nature, it also brings new possibilities of manipulating matter on a quantum scale.
https://www.tuwien.ac.at/en/news/news_detail/article/124456/
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