Researchers establish a robust theoretical description of many-body localization (MBL) —a phenomenon that prevents quantum many-body systems from reaching equilibrium. This advancement enables understanding and demonstrating MBL in a wider range of quantum many-body systems.
Researchers experimentally demonstrate that the light emitted after a high harmonic generation process in semiconductors is entangled and squeezed, two unmistakable signs of quantum light.
An international team of researchers present in Reports on Progress in Physics Original Research a numerical experiment that demonstrates the possibility to capture topological phase transitions via an x-ray absorption spectroscopy scheme. By overcoming previous energy resolution limitations, the method will enable further investigations on relevant systems for optoelectronics applications.
An ICFO team, in collaboration with international partners, publishes in Nature a new method that, for the first time, achieves valley polarization in centrosymmetric bulk materials universally, without reliance on specific materials. This “universal technique” could have significant implications for controlling and analyzing various properties of both 2D and 3D materials. Such advancements could drive progress in fields like information processing and quantum computing.
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A team of researchers and OPTOlogic team members theoretically prove that the emitted light after a high harmonic generation (HHG) process is not classical, but quantum and squeezed. The study unveils the potential of HHG as a new source of bright entangled and squeezed light, two inherent quantum features with several cutting-edge applications within quantum technologies.
A team of researchers, including members from the Optologic team, theoretically proposes a new experimental platform based on analog simulation with atom clouds to study high-harmonic generation. This ultrafast dynamic process challenges conventional computational methods. Their simulator allows for adaptation to approach a wide range of complex phenomena, opening doors to regimes that theory and direct experimentation struggle to reach.
Despite all the successes in understanding electron dynamics at their natural attosecond (one quintillion of a second) time scale, one of the fundamental processes core to this field, high-harmonic generation (HHG), raises new challenges for cold-atom simulation. It consists in a highly non-linear phenomenon where a system absorbs many photons of an incoming laser and emits a single photon of much higher energy.
The unique characteristics of HHG make it an exceptional source of extreme ultraviolet radiation and consequently of attosecond pulses of light, which has important applications to various fields such as nonlinear optics or attosecond science.
The high number of variables involved hinders the study of this process, aside from its ultrafast speed. In any given material, many atoms and electrons are present, so studying most of the occurring chemical processes in all their complexity would require not only describing all these components but also their interactions with external fields and even among themselves. This task proves to be extremely challenging for any current classical computer. An alternative route involves using quantum devices, building the so-called analog simulators, whose nature allows them to better capture the complexity of the system.
Now, ICFO researchers Javier Argüello, Javier Rivera, Philipp Stammer led by the ICREA Prof. at ICFO Maciej Lewenstein and in collaboration with other institutes all over the globe (Aarhus University, University of California and Guangdong Technion-Israel Institute of Technology) have proposed, in a Physical Review X Quantum publication, an analog simulator to access the emission spectrum of HHG using ultracold atomic clouds. Besides showing that an accurate replication of the key characteristics of the HHG processes in atoms was possible, they also provide details on how to implement it to specific atomic targets and discuss the main sources of errors.
An analog simulator allows scientists to study a complex quantum system (computationally challenging) through the control and manipulation of a much simpler one, which can be addressed experimentally. However, not every choice is valid, a connection between both systems must exist.
In this particular work, the researchers chose the complex phenomenon of high-harmonic generation to benchmark their idea. In this process, atomic bound electrons tunnel out the barrier formed by the atomic Coulomb potential and a laser electric field. Then, those free electrons accelerate, causing the emission of radiation with characteristic harmonic frequencies upon recombination with their parent ions. This emission spectrum of HHG is what the researchers aimed to recover.
On the other hand, they achieved connection to a much simpler quantum system by conveniently replacing certain components. Instead of an electron and a nuclear potential, they proposed using an atomic gas trapped by a laser beam; and instead of the incoming light and its electric field, they suggested an external magnetic gradient that could be tuned at will. It turns out that the absorption images of this engineered system coincide with the desired emission yield.
Therefore, by taking absorption images of the analog simulator, the emission spectrum of the atomic high-harmonic generation can be indirectly studied.
In the end, the research group has demonstrated the potential of their alternative method for addressing complex systems that would otherwise only be theoretically approximated. They proved that state-of-the-art analog simulators can retrieve the HHG emission spectrum, establishing correspondence between experimental and simulated parameters and providing an exhaustive experimental analysis.
Moreover, the platform offers twofold advantages. Firstly, scientists can easily tune the elements that emulate the incoming field and the nuclear potential. Secondly, the simulation also provides temporal magnification, allowing scientists to work in a much slower (and thus practical) frame by avoiding the attosecond time-scale.
The team emphasizes their approach’s adaptability, which is not limited to exclusively simulating HHG but could be extended to other, more exotic configurations. Specifically, ultrafast processes such as multielectronic dynamics or the reaction of matter to non-classical light could benefit the most.
An international team of researchers from the European XFEL, along with colleagues from the Max-Born Institute in Berlin (partners of OPTOlogic), Universities of Berlin and Hamburg, The University of Tokyo, the Japanese National Institute of Advanced Industrial Science and Technology (AIST), the Dutch Radboud University, Imperial College London, and Hamburg Center for Ultrafast Imaging, have presented new ideas for ultrafast multi-dimensional spectroscopy of strongly correlated solids. This work has now been published in Nature Photonics.
Cartoon view of the key many-body states corresponding to the spectroscopic signal at energies of the LHB, QP and UHB.
“Strongly correlated solids are complex and fascinating quantum systems in which new electronic states often emerge, especially when they interact with light” says Alexander Lichtenstein from Hamburg University and Eu-XFEL. Strongly correlated materials, including high-temperature superconductors, certain types of magnetic materials, and twisted quantum materials, challenge our fundamental understanding of the microcosm. Moreover, they offer opportunities for many exciting applications ranging from materials science to information processing to medicine. For example, superconductors are used by MRI scanners. Understanding the hierarchy and interplay of the diverse electronic states arising in strongly correlated materials is very important.
At the same time, these materials challenge our experimental and theoretical tools because transformations between these states often involve phase transitions. Phase transitions do not develop smoothly from one stage to the next but may occur suddenly and quickly, particularly when light interacts with the material. How do pathways of charge and energy flow during such a transition? How quickly does it occur? Can light control it and sculpt the electron correlations? Can light bring the material into a state that it wouldn’t find itself in under usual circumstances? Powerful and sensitive devices like X-ray lasers such as the European XFEL in Schenefeld near Hamburg, and modern optical tools of attosecond science (1 attosecond = 10^-18 sec), address these types of questions.
In their work, the international team now presents a completely new approach that makes it possible to monitor and decipher the ultrafast charge motion triggered by a short laser pulse illuminating a strongly correlated system. They have developed a variant of ultrafast multi-dimensional spectroscopy, taking advantage of the attosecond control of how multiple colors of light add to form an ultrashort laser pulse. The sub-cycle temporal resolution offered by this spectroscopy shows the complex interplay between the different electronic configurations and demonstrates that a phase transition from a metallic state to an insulating state can take place within less than a femtosecond – i.e. in less than one quadrillionth of a second.
“Our results open up a way of investigating and specifically influencing ultrafast processes in strongly correlated materials that goes beyond previous methods” says Olga Smirnova from the Max-Born Institute and Berlin TU, awardee of the Mildred Dresselhaus prize of the Hamburg Centre for Ultrafast Imaging, “we have thus developed a key tool for accessing new ultrafast phenomena in correlated solids”.
Reference: Sub-cycle multidimensional spectroscopy of strongly correlated materials, V. N. Valmispild, E. Gorelov, M. Eckstein, A. I. Lichtenstein, H. Aoki, M. I. Katsnelson, M. Yu. Ivanov & O. Smirnova, Nature Photonics (2024)
An international team of researchers reports on a new method that permits inducing symmetry-protected higher-order topology through a spontaneous symmetry-breaking mechanism in a two-dimensional system of ultra-cold bosonic atoms inside a cavity.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 899794. Funding call: H2020-FETOPEN-2018-2019-2020-01.
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