[23.02.2022] Correct counting determines our modern life - whether it is the bits in the computer with their two states, the number of positive corona tests, or in general any system which has countable events. But the faster the counting is done and the smaller the signals are, the more likely data can be lost in the noise. The theoretical physicist Eric Kleinherbers from CRC1242 and CENIDE has now developed a new tool that sheds more light on such data.

Counting statistics is especially important in the quantum world. Modern measuring instruments are so sensitive that they can detect single quantum jumps. Limiting factors are the time resolution of the detector, the background noise, and the observation time. The resulting detection errors distort the measured information, so that no or wrong conclusions may be drawn about the underlying quantum dynamics. For their work, the researchers used so-called self-assembled quantum dots, which have similar properties to individual atoms, and employed a trick. The quantum dot is excited with a laser and radiates back light particles (photons) as long as it is "empty." If an additional electron enters the quantum dot, the light current breaks off. In this way, the electron occupation can be recorded in real time by the photons and subsequently statistically evaluated. 

To test how robust the new evaluation algorithm is, data was deliberately deleted from the original data set, simulating an erroneous measurement. "These were typical experimental errors: signals that are too fast for the detector and are, therefore "missed" or a spike in the noise that fakes a signal" explains Eric Kleinherbers, lead author of the study. By comparing the original readings with the erroneous data, the researchers were able to demonstrate that the new method of analysis is much more error-tolerant than the standard methods of statistical analysis used previously. This makes the actual behavior of electrons and photons more visible, shedding light on the quantum world. "So far, it's a bit like trying to put a screw in the wall with an improper screwdriver," Kleinherbers explains. "It works, but it's not pretty. Now we have the right tool for analyzing the data."

Counting statistics is everywhere: in the evaluation of nerve signals as well as in radioactive decay, in microelectronics, and in magnetism. While experimental physicists are constantly coming up with new measurement techniques and experiments, theorists are also pushing the limits of feasibility with new evaluation methods. The developed method is not only interesting for new measurement results - existing data can now also be examined more closely, as Kleinherbers says. "We are in close exchange with colleagues who now want to see what else might be hidden in their data."

The results were published in the journal Physical Review Letters (DOI: 10.1103/PhysRevLett.128.087701).

[22.01.2022] Bi-stable spin-crossover molecules with an abrupt and wide hysteric spin-state switching in the room temperature regime are promising candidates for future molecule-based switching and memory applications. Especially for the analysis of the ultrafast non-equilibrium dynamics in spin-crossover molecules, e.g., with pump-probe experiments which we want to perform within Project A05 in the CRC1242, those criteria are of crucial importance. A joint paper (DOI: 10.1002/chem.202103853), written under the leadership of Dr. Senthil Kumar Kuppusamy (AG Ruben, KIT) within the framework of the Projects A05 and C05, reports two Fe(II) spin-crossover complexes that show these technically relevant criteria and was recently chosen to be a cover feature of Chemistry - A European Journal.

[01.09.2021] From November 8 to 10, 2021 the collaborative research centers SFB 1242 "Non-equilibrium Dynamics of Condensed Matter in the Time Domain" (University of Duisburg-Essen) and SFB/TRR 270 "Hysteresis design of magnetic materials for efficient energy conversion" (Technical University of Darmstadt and University of Duisburg-Essen) established by the German Research Foundation will host the 25th German Female Physicists' Conference. The target group of the digital event is female physicists from various disciplines and career stages - from students to professors, from interns to industrial physicists in top management - and all interested persons.

Further information can be found here

During the pandemic, many conferences have moved towards an on-line format. This is also true for the biannular LEEM/PEEM conference, which focuses on low energy microscopy and photoemission microscopy. Ph.D. candidate David Janoschka had the opportunity to present his research on vector microscopy during the on-line conference as a video-poster. Follow the link to see his poster and enjoy a journey into our femtosecond microscopy lab.

The complete video can be found here

[24.04.2020] The duration of their snapshot relates to one second as one second relates to the age of the universe: In a joint collaboration with Australian Scientist Tim Davis and the Group around Harald Gießen from Stuttgart, Physicists from the Center for Nanointegration (CENIDE) at the University of Duisburg-Essen (UDE) have developed ultrafast vector microscopy as a way of determining electric fields on surfaces with high temporal and spatial resolution. The new method was used to measure the dynamics of optical skyrmions in the time domain for the first time. The renowned journal "Science" publishes this breakthrough in nanooptics in its current issue.

Original publication:

“Ultrafast vector imaging of plasmonic skyrmion dynamics with deep subwavelength resolution”, Davis et al.

(DOI: 10.1126/science.aba6415)

[01.10.2019] Prof. Sebastian Schlücker from the Faculty of Chemistry is keen to promote MINT subjects as early as primary school. Together with colleagues, he therefore distributes specially developed experiments with appropriate teaching/learning material. His idea won him 3rd place in the UDE's small business management (sbm) start-up competition. Congratulations!

Read more.

[27.09.2019] Colloquially, the term “quantum jump” is used to describe a tremendous development. In fact, it is the smallest change of state that can still be traced. Physicists from the Collaborative Research Center 1242 at the UDE have now succeeded in measuring every single jump by optical means and drawing conclusions about the dynamics of the electrons inside a quantum dot. The journal Physical Review Letters reports on this in its 122^nd issue.

The experimental setup included a quantum dot – i.e. a solid structure of only about 10,000 atoms – next to a reservoir with electrons. About 100 times per second an electron jumps back and forth between this structure and the reservoir. It can jump into a high or low energy state into the quantum dot and change inside from top to bottom. For the first time, the researchers were able to observe this change through these tiny jumps.

Read more.

[14.06.2019] Phase-change materials (PCMs) are used in the latest generation of smartphones enabling higher storage densities and energy efficiency. When an electrical or optical pulse is applied to heat these materials locally, they change from a glassy to a crystalline state, and vice versa. These two different states represent the ‘0’ and ‘1’ of the binary code needed to store information. An international team of researchers led by Klaus Sokolowski-Tinten has now succeeded in observing the processes that occur during switching – something that has never been done before because of the short time-scales involved. They used the ultrashort and extremely brilliant X-ray pulses from an X-ray Free Electron laser to resolve the atomic structure changes of two Sb-based PCMs during the entire switching cycle. They found that two liquid states of the materials are involved in the process – one that has more rigid chemical bonds, and which helps stabilize the glassy “off” state at ambient conditions, and one that is rather metallic and can therefore crystallize very quickly to produce the “on” state. These results provide a microscopic understanding on how PCMs work and why some materials are PCMs and others not. More generally, this work and the applied time-domain approach can also help to understand how liquids of other classes of materials behave when they are rapidly super-cooled to temperatures well below the melting point and why some liquids are more likely to form a glass than others. The study, published on June 14th in Science, was coordinated by the University of Duisburg – Essen and European XFEL and carried out at the Linac Coherent Light Source of SLAC National Accelerator Laboratory (Menlo Park, USA). It was was part of an international collaboration including scientists from Forschungszentrum Jülich, Institut Laue-Langevin, Lawrence Livermore National Laboratory, Lund University, Paul Scherrer Institute, SLAC National Accelerator Laboratory, Stanford University, The Spanish National Research Council (CSIC), University of Aachen, and the University of Potsdam.

Original publication:

“Femtosecond X-ray diffraction reveals a liquid-liquid phase transition in phase-change materials”, Zalden et al.

DOI: 10.1126/science.aaw1773

[13.06.2019] Dr. Nora Dörmann has received the Diversity Award of the University of Duisburg-Essen in the category "Managers". The prize was presented on 6 June as part of the Diversity Day by Prorector Prof. Dr. Barabara Buchenau and the speaker of the SFB 1242 Prof. Dr. Uwe Bovensiepen, who also gave the laudatory speech. Mrs. Dörmann is the managing director of the SFB 1242. The prize was awarded in recognition of her commitment to the promotion of women scientists.

[26.02.2019] In the 19th century, Augustin Jean Fresnel invented his zone-plate; basically a hologram, which - by diffraction - forms a defined focal point if illuminated with a plane light wave. Frank Meyer zu Heringdorf's  TR-PEEM Team has now applied the concept of Fresnel-focusing to surface-plasmon-polaritons, i.e., to electron-density waves that can propagate at metal surfaces with almost the speed of light in vacuum. Instead of focusing traveling plasmon waves by a Fresnel type zone plate, however, the team structured particular Fresnel-type grating couplers that were illuminated by femtosecond laser pulses, and that very effectively excited plasmon waves forming a focus at a desired location. Using their time-resolved photoemission microscope, the team could characterize this  "Fresnel-optics for surface plasmon waves" in detail, and they could follow the formation of the focus in a super-slow motion movie on the femtosecond time-scale. The results were now published in ACS Photonics.