X-ray four-wave mixing captures elusive electron interactions inside atoms and molecules

Amazing stuff!

"Scientists at the X-ray free-electron laser SwissFEL have realized a long-pursued experimental goal in physics: to show how electrons dance together. The technique, known as X-ray four-wave mixing, opens a new way to see how energy and information flow within atoms and molecules. In the future, it could illuminate how quantum information is stored and lost, eventually aiding the design of more error-tolerant quantum devices. ..."

"... In many quantum technologies – not least quantum computing – information is stored in delicate patterns of these interactions, known as coherences. When these coherences are lost, information disappears – a process known as decoherence. Learning how to understand and ultimately control such fleeting states is one of the major challenges facing quantum technologies today. ...

Scientists  ... have now developed a way to access them using a technique known as X-ray four-wave mixing. ...

Conceptually, X-ray four-wave mixing is similar to nuclear magnetic resonance (NMR), which today is used daily in hospitals for MRI scans. Both techniques use multiple pulses to create and read out coherences in matter.  ...

X-rays bring this same kind of powerful approach to a smaller scale and allow us to step into the world of the electrons. “Whereas other approaches tell us about how atoms or molecules as a whole interact with each other or with their surroundings, with X-rays we can zoom right in to the electrons,” ..."

From the abstract:

"Coherent nonlinear light–matter interaction with X-rays gives access to a regime in ultrafast spectroscopy in which atomic resolution meets femtosecond and attosecond timescales.

Particularly, X-ray four-wave mixing, involving several resonant transitions in a single coherent nonlinear process, has the potential to provide information on the electronic states coupling, coherent electron motion, correlation and dynamics, with state and site selectivity.

Here we demonstrate coherent, background-free four-photon interactions with core-shell electrons using single broadband X-ray pulses from a free-electron laser. The all-X-ray four-wave mixing signals, measured in gaseous neon, arise from doubly resonant nonlinear processes involving Raman transitions, including X-ray coherent anti-Stokes electronic Raman scattering.

The 2D spectral maps (photon-in/photon-out) represent a step towards multidimensional correlation spectroscopy at the atomic scale.

Using a multicolour time-delayed X-ray pulse scheme, we further demonstrate the feasibility of extending the proposed methodology to the ultrafast time domain. These results reveal potential for studying localized electron dynamics in multiple systems, from biomolecules to correlated quantum materials, with applications in areas such as energy conversion, biomedical imaging and quantum information technologies."

X-ray four-wave mixing captures elusive electron interactions inside atoms and molecules

Swiss X-ray laser reveals the hidden dance of electrons (original news release) "Scientists at the X-ray free-electron laser SwissFEL have realised a long-pursued experimental goal in physics: to show how electrons dance together. The technique, known as X-ray four-wave mixing, opens a new way to see how energy and information flow within atoms and molecules. In the future, it could illuminate how quantum information is stored and lost, eventually aiding the design of more error-tolerant quantum devices. The findings are reported in Nature."

Coherent nonlinear X-ray four-photon interaction with core-shell electrons (no public access)

Coherent all X-ray four wave mixing at core shell resonances (preprint, open access)

Figure 1:Scheme of the experimental setup and spatial characterization of the XFWM signal