Coherent control with X-rays

Operating nuclear X-ray quantum systems is challenging, due to the extreme scales involved. In recent years, the availability of large scale X-ray facilities has kicked off a “source-driven revolution” [1], with many X-ray photons and excellent beam quality being available. However, this is where the ultra-narrow resonances become a challenge, since even a very well monochromatized X-ray beam is orders of magnitude broader than the transition linewidth, such that only few photons excite the transition.

To overcome this challenge and to be able to employ concepts from visible quantum optics, it is necessary to develop novel control techniques and optimized setups. X-ray cavity QED is one avenue in this direction. Another avenue is coherent control, which is a paradigm across the optical sciences.

Next to my main projects, I also contribute to this experimental development. As an example, we designed a setup where a broad spectrum from an X-ray source is “sharpened” by shoveling photons onto the resonance energy [a], taking previous experiments using time-domain pulse shaping [2] to the spectral domain. The basic idea is to use forward scattering and a mechanical “digger” (see figure) given by a piezo-electric transducer, whose motion can be controlled. This idea of spectral shaping in the hard X-ray domain may find broad applications with ultra-narrow resonances to increase photon count rate by at least an order of magnitude, which may make new experiments possible.

In follow-up experiments, we are taking this idea one step further. In a recent preprint [b], we demonstrate how these concepts can be employed for coherent X-ray optical control of nuclear dynamics. A multi-dimensional detection technique allows us to track the nuclear excitation and to contol it subsequently via the piezo motion. In nuclear resonance scattering, this constitutes a paradigm shift away from characterization and optimization of the light field to nuclear observables. As an interesting side-note, our experiment broke the previous world-record [3] for interferometric stability in the time-domain, as measured by the so-called Allan deviation [4].

External references

[1] G. K. Shenoy and R. Röhlsberger, Hyperfine Interactions 182, 157 (2008)
[2] F. Vagizov et al. Nature 508, 80–83 (2014)
[3] D. E. Laban et al. Phys. Rev. Lett. 109, 263902 (2012)
[4] D. Allan, Proc. IEEE 54, 221 (1966)

Related publications

[a] K. P. Heeg et al. Science 357, 375 (2017)
[b] K. P. Heeg et al. arXiv:2003.03755 (2020)