Transparency is generally a property of a material’s density or
crystal structure, and varies depending on the wavelength of
light. However, transparency can also be achieved by exploiting quantum interference between energy level transitions in atoms. Up until now, such transparency has been confined to optical
wavelengths, due to the
typical energies of atomic transitions.
Transitioning between energy levels within atomic nuclei (instead of electron transitions) involves much
higher energies, corresponding to hard X-ray frequencies. Ralf
Röhlsberger, Hans-Christian Wille, Kai
Schlage, and Balaram Sahoo of the Deutsches Elektronen-Synchrotron (DESY) in
Germany have induced transparency in iron-57 nuclei, using an X-ray
laser to drive the nuclei to resonance. The experiment not only made
the iron nuclei nearly vanish, but also slowed the X-ray photons to a
small fraction of their usual speed. This result holds out the
tantalizing possibility of quantum optics in the nuclear regime,
providing us new ways of manipulating light at far higher energies than
have previously been possible.
from Ars Technica