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 together 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, which include high-temperature superconductors, certain types of magnetic materials, and twisted quantum materials among others, both challenge our fundamental understanding of the microcosm and offer opportunities for many exciting applications ranging from materials science to information processing to medicine: for example, superconductors are used by MRI scanners. This is why understanding the hierarchy and the interplay of the diverse electronic states arising in strongly correlated materials is very important.
At the same time, it challenges our experimental and theoretical tools, because transformations between these states are often associated with phase transitions. Phase transitions are transformations that do not develop smoothly from one stage to the next but may occur suddenly and quickly, in particular when the material is interacting with light. What are the pathways of charge and energy flow during such a transition? How quickly does it occur? Can light be used to control it and to sculpt the electron correlations? Can the light bring the material into a state that the material wouldn’t find itself in under the usual circumstances? These are the types of questions that can be addressed with powerful and sensitive devices like X-ray lasers such as the European XFEL in Schenefeld near Hamburg, and/or with the modern optical tools of attosecond science (1 attosecond = 10-18 sec).
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 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.
Last December 11th, the consortium of OPTOlogic gathered at ICFO to discuss the progress of the project. Hosted by the Barcelona partnering institution, partners from Max Born Institute, CEA, Fritz Haber Institute -Max Planck and LightON came to the center to meet in person and review the progress of the project, share the latests results from the different partners, brainstorm on novel theories that could be applied to the field, discuss on possible solutions to overcome a few challenges that have arises within the project, and most of all see where they are at and plan following steps to take to complete the objectives in the last phase of the project.
As you may know, the project has the objective of understanding light-matter interactions in 2D materials and aim to control the properties of these materials through light. During the entire day, in-depth discussions and vivid interactions between the partners revolved on how to achieve control of these interactions at attosecond timescales and study the dynamics of materials when you apply these such ultra-fast pulses of light to the layers of material, delving into the world of high harmonic generation, trefoil fields, phonons, excitons, electronics structures, logic operations, valleytronics, and many more.
The meeting ended with a visit to lab of the Attosecond and Ultra-Fast Optics research group led by Jens Biegert, who showed the consortium partners a glimpse of the facilities and the science being carried out for the project.
ICREA Prof at ICFO Maciej Lewenstein is among members selected in this year’s class.
The Board of Directors of Optica (formerly OSA) recently elected 129 members from 26 countries to the Society’s 2024 Fellow Class. Optica Fellows are selected based on several factors, including outstanding contributions to research, business, education, engineering and service to Optica and its community. ICREA Professor at ICFO Dr. Maciej Lewenstein was among the members selected to belong to this year’s Fellows Class “for outstanding theoretical contributions to atto-optics, atto-science, quantum optics, and quantum information.”
“Congratulations to the 2024 class of Optica Fellows,” said Michal Lipson 2023 Optica President. “It is a pleasure to honor these members who are advancing our field and society. We are grateful for their exceptional work and dedication.”
Fellows are Optica members who have served with distinction in the advancement of optics and photonics. The Fellow Members Committee, led by Chair Ofer Levi, University of Toronto, Canada, reviewed 216 nominations submitted by current Fellows. As Fellows can account for no more than 10 percent of the total membership, the election process is highly competitive. Candidates are recommended by the Fellow Members Committee and approved by the Awards Council and Board of Directors.
The new Fellows will be honored at Optica conferences and events throughout 2024.
About Optica
Optica (formerly OSA), Advancing Optics and Photonics Worldwide, is the society dedicated to promoting the generation, application, archiving and dissemination of knowledge in the field. Founded in 1916, it is the leading organization for scientists, engineers, business professionals, students and others interested in the science of light. Optica’s renowned publications, meetings, online resources and in-person activities fuel discoveries, shape real-life applications and accelerate scientific, technical and educational achievement.
In a recently study published in Reports on Progress in Physics, researchers Irénée Frérot, Matteo Fadel and ICREA Prof. at ICFO Maciej Lewenstein, review methods that allow one to detect and characterize quantum correlations in many-body systems, with a special focus on approaches which are scalable.
Maciej Lewenstein gives a brief overview about the study in the following video abstract:
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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