Coherent storage and phase modulation of single hard x-ray photons using   nuclear excitons
  Coherent storage and phase modulation of x-ray single-photon wave packets in resonant scattering of light off nuclei is investigated theoretically. We show that by switching off and on again the magnetic field in the nuclear sample, phase-sensitive storage of photons in the keV regime can be achieved. Corresponding $\pi$ phase modulation of the stored photon can be accomplished if the retrieving magnetic field is rotated by $180^{\circ}$. The development of such x-ray single-photon control techniques is a first step towards forwarding quantum optics and quantum information to shorter wavelengths and more compact photonic devices. 
Wen-Te Liao, Adriana P\'alffy and Christoph H. Keitel
physics.atom-ph quant-ph