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A new protocol for measurement developed at TU Wien will help in the measurement of the quantum phase of electrons. This is a significant step in attosecond physics. The work appears in the Physical Review Letters.

The current methods in attosecond physics help to measure very short intervals of time. We can track physical processes with very high precision, attoseconds to be precise which is equal to billionths of a billionth of a second.

This can be done using short laser pulses. The ionisation of one atom can be studied along with the process in which an electron exits the atom. Electrons do not always display the particle properties since the quantum-physical wave behaviour plays a major role. It is a wave oscillating in a very short time scale. The task to measure the cycle duration of such oscillations is challenging, however, it is even more difficult to measure the phase. Questions such as how would the electron waves oscillate if an electron can be ionized in two ways get quite tricky. 

A group of researchers from TU Wien and CREOL College, University of Central Florida has developed a protocol for measuring the phase of the electron waves. This can help in understanding photovoltaics in a better manner. 

Stefan Donsa, a team member working under Prof. Joachim Burgdörfer, Institute for Theoretical Physics, TU Wien mentioned that a wave consists of crests and troughs. Its phase tells the location of these points in space and time. Perfect overlapping of quantum waves, such that every wave peak meets a wave peek of other one adds up the waves, on the other hand, if the crest superimposes with the trough then they get cancelled. Hence phase shifts are very important in quantum physics. For this, a reference clock is needed that can make sure the overlap occurs at the exact time without any shift. The latest measurement protocol uses an atomic process as a reference for the other one. 

Helium atoms have been studied in computer simulations where a photon absorption results in emission of an electron. This ejected electron has a certain phase that is difficult to measure. The trick of the new method is to add a second quantum effect serving as a clock, i.e. a quantum metronome. The atom can absorb two photons instead of one under specific conditions. It leads to the same event, an electron emitted with particular energy but this can be measured as it has a different phase. Complicated protocols are needed in attosecond physics. Although there are many such protocols, none allows for the direct measurement of the phase of electron. 

Stefan Donsa said that this measurement protocol allows for the translation of information about an electron phase to its spatial distribution by a combination of special laser pulses. The right laser pulses can help in getting the phase information from the electron’s angular distribution. 

The protocols have to be experimented now to identify which quantum mechanical information can actually be obtained. 

Journal Reference: Physical Review Letters.



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