A technique has been developed for storing X-ray photons while preserving all quantum properties

A technique has been developed for storing X-ray photons while preserving all quantum properties

Scientists who study the nature of photons seek to “tame” this particle and manipulate it in the same way that electron researchers manipulate electrons. Today physicists have partly managed to achieve some results, however, regarding the visible and infrared spectra.

Based on advances in the short-term delay of X-ray radiation through nuclear excitations, German physicists have developed a technique that allows you to store a photon in the X-ray spectrum. According to scientists, the achievement allows you to immediately “capture” a photon in the so-called “trap”, after which the particle can be released, and the properties of the photon will remain unchanged. The work of German scientists is an important step towards the development of experimental photonic systems that can use shorter wavelengths to accommodate a large number of active elements in a small space.

Back in the mid-90s of the last century, a German group of scientists from the University of Hamburg carried out experiments on the delayed decay of an excited nucleus for iron (Fe-57). The essence of the experiment was that a polarized X-ray flux with an energy of 14.4 keV, equivalent to the energy of the nucleus, was emitted towards the nucleus in the perpendicular direction. After that, the ground state of the atom was split into 2, and the excited state into 4 sublevels. The parameters of the experiment were chosen in such a way that each ground state passed to only one excited state. Thus, only 2 excitation sublevels remained filled. Ultimately, the position of the atom looked like a superposition composed of the two noted states, and since the magnetic properties in different states were different, the decay of the atom to the ground state varied in time.

After a few seconds, the scientists connected an additional magnetic field directed perpendicular to the main one. After changing the direction, the magnetic field “pulled” into itself all the sublevels of the excited state. Thus, physicists have demonstrated that if the procedure is repeated at a certain time in relation to fluctuations in the probability of decay of an excited state, then the probability of decay decreases. After turning off the magnetic field, the state decayed, which led to a new emission of an X-ray photon, while the photon energy was equal to the pulse energy. However, the problem for scientists was that the rest of the quantum properties of the photon were not preserved.

To solve the problem, scientists from another German institution – the Max Planck Institute for Nuclear Physics – proposed to change the existing methodology. The experiments also involved X-rays, “attacking” the Fe-57 target in a magnetic field. By changing the intensity and concentration of iron atoms, physicists provoked the appearance of only one Fe-57 atom during the cycle. Instead of turning on an additional magnetic field, as in previous experiments, scientists proposed, on the contrary, to turn off the main field at a strictly specified moment of oscillation of the excited state – 10 nanoseconds after the activation of the X-ray pulse.

According to the calculations of the researchers, such an excited state is blocked, which does not allow it to decay. After the magnetic field is reactivated, the state decays with the emission of a photon of the X-ray spectrum, the properties of which completely coincide with the properties of the original particle that causes excitation. Thus, physicists have achieved that the X-ray photon can be stored for 100 nanoseconds. A feature of the developed method of particle conservation is that when the magnetic field changes to the opposite, the phase of the photon of the X-ray spectrum also changes to the opposite.

To date, the results of studies of a photon in the X-ray spectrum look rather meager when compared with similar experiments in the visible spectrum. Despite this, theoretical research by physicists can be the first step towards creating photonic devices operating at short wavelengths.

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