Multiple images of two objects located between two parallel mirrors illustrate the principle of electromagnetically induced transparency of atomic nuclei: The interaction of x-rays with two layers of iron within such a system of mirrors (an optical resonator) leads to a quantum mechanical superposition state of iron and its mirror images that causes the iron atomic nuclei to appear transparent. Photo: DESY
This kind of sandwich with a total thickness of only 50 nanometres is irradiated under very shallow angles with an extremely thin X-ray beam from the PETRA III synchrotron light source. Within this mirror system, the light is reflected back and forth several times, generating a standing wave, a so-called resonance. When the light wavelength and the distance between both iron layers are just right in proportion, the scientists can see that the iron becomes almost transparent for the X-ray light. In order for this effect to occur, one iron layer must be located exactly in the minimum (node) of the light resonance, the other one exactly in the maximum.When the layers are shifted within the cavity, the system immediately becomes non-transparent. The scientists attribute this observation to a quantum-optical effect, caused by the interaction of atoms in the iron layers. Unlike single atoms, the atoms in an optical cavity together absorb and radiate in synchrony. In the geometry of this experiment their oscillations mutually cancel each other, as a result of which the system appears to be transparent. In contrast to previous experiments in the optical regime, only few light quanta are necessary to generate this effect.
The experiments of the DESY scientists also showed another parallel to the EIT effect: the light trapped in the optical cavity only travels with the speed of a few metres per second – normally it is nearly 300 000 kilometres per second. With further experiments, the scientists will clarify how slow the light really becomes under these circumstances, and whether it is possible to use this effect scientifically. A possible application and at the same time an important building block on the way to light-quantum computers is, for example, the storage of information with extremely slow or even stopped light pulses.
Dr. Thomas Zoufal | idw
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