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New Approach to Ultrafast Multi-Dimensional Spectroscopy
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.
The Complexity of Strongly Correlated Solids
“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.
Challenges of Studying Phase Transitions
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.
A New Approach to Monitor Ultrafast Charge Motion
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.
New Tools for Investigating Ultrafast Processes
“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)
On December 11th, the consortium of OPTOlogic gathered at ICFO, hosted by Barcelona, to discuss the ongoing progress of their project. In addition to the host institution, partners from Max Born Institute, CEA, Fritz Haber Institute – Max Planck, and LightON were present. This in-person meeting provided an opportunity to thoroughly review the project’s advancements, share the latest research findings, and collectively brainstorm novel theories applicable to their field of study. Furthermore, the consortium engaged in discussions to address challenges encountered within the project and to meticulously plan the subsequent steps necessary to achieve their objectives in the final phase.
As a brief overview, the project aims to gain a comprehensive understanding of light-matter interactions in 2D materials and ultimately control the properties of these materials through light manipulation. Throughout the course of the day, partners actively participated in in-depth discussions and lively interactions, with a particular focus on achieving control of these interactions at attosecond timescales. In greater detail, they delved into studying the dynamic behavior of materials when exposed to ultra-fast pulses of light, exploring various phenomena such as high harmonic generation, trefoil fields, phonons, excitons, electronic structures, logic operations, valleytronics, and more.
To conclude the productive meeting, the consortium visited the lab of the Attosecond and Ultra-Fast Optics research group, led by Jens Biegert. During this visit, the partners gained valuable insights into the state-of-the-art facilities and the cutting-edge science being conducted in direct support of the project’s goals.
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Light-matter interactions in 2D materials
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 selects Fellows based on several factors, including outstanding contributions to research, business, education, engineering, and service to Optica and its community. Thus, ICREA Professor at ICFO Dr. Maciej Lewenstein joins 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.”
Optica recognizes Fellows who have served with distinction in advancing optics and photonics. Specifically, Chair Ofer Levi from the University of Toronto, Canada, led the Fellow Members Committee, which reviewed 216 nominations submitted by current Fellows. Since Fellows can account for no more than 10 percent of the total membership, the election process remains highly competitive. Consequently, the Fellow Members Committee recommends candidates, and the Awards Council and Board of Directors approve them.
Optica will honor the new Fellows at conferences and events throughout 2024.
About Optica
Optica (formerly OSA), Advancing Optics and Photonics Worldwide, promotes the generation, application, archiving, and dissemination of knowledge in the field. Founded in 1916, it leads as the premier 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.
Peng Ye, CEA partner, attended the Paris Saclay International School on Ultra-fast X-rays Science conference and presented a poster in representation of the project.
The Institute for the Sciences of Light of Paris-Saclay University organizes the “Paris-Saclay Ultrafast X-ray Science School” in collaboration with “The Frontiers of Attosecond and Ultrafast X-ray Science School” of Erice (Italy). This thematic school occurs every other year at Paris-Saclay University, alternating with the School of Erice.
Ultrafast X-ray Science 2022
The 1st edition in France will take place October 10-14, 2022. It aims to provide the audience with a general view of the fundamental concepts and basics of ultrafast X-ray and attosecond science, as well as on a series of applications. It will cover topics spanning from the development of ultrafast light sources of visible, XUV, and X-ray radiation, including High Harmonic Generation and Free Electron Lasers, to the study of quantum systems in different states of matter, in both gas and condensed phases.
The School offers a high-profile training opportunity for newcomers in the field, such as master and PhD students, as well as postdocs and junior researchers. Additionally, it provides a chance to discover the laboratories of Paris-Saclay University in the area of the Sciences of Light. Distinguished lecturers each provide two one-hour lectures on a general topic, scheduled on two different days. Moreover, they also give a seminar describing their own research, thus giving insight into current hot research topics. The lecturers remain available for informal post-course discussions most of the week.
The schedule includes numerous opportunities for informal exchanges, from common meal times (including breakfast) to generous poster sessions. Furthermore, an afternoon focuses on on-campus laboratory visits, and a cultural afternoon in Paris complements the program.
PARIS SACLAY INTERNATIONAL SCHOOL ON ULTRAFAST X-RAYS SCIENCE
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:
Nobel Prize for Attosecond Pulse Development
Pierre Agostini, Ferenc Krausz, and Anne l’Huillier receive the Nobel Prize “for developing experimental methods that generate attosecond pulses of light for studying electron dynamics in matter.” (Attosecond Pulse Development)
Revolutionizing Electron Dynamics
The three Nobel Laureates in Physics 2023 are being recognized for their experiments, which have provided humanity with new tools for exploring the world of electrons inside atoms and molecules. Pierre Agostini, Ferenc Krausz, and Anne L’Huillier have demonstrated a way to create extremely short pulses of light that can measure the rapid processes in which electrons move or change energy.
Groundbreaking Discoveries in Attoscience
Last October, the Royal Swedish Academy of Sciences announced the laureates of the 2023 Nobel Prize in Physics, naming three ground-breaking scientists in the field of Attoscience, Anne L’Huillier, Pierre Agostini, and Ferenc Krausz for “developing experimental methods that generate attosecond pulses of light for studying electron dynamics in matter.”
Congratulations from the ICFOnians
ICFOnians enthusiastically congratulate these friends and colleagues for their landmark achievements and for the highest recognition for their work that this Nobel Prize implies.
Unveiling Processes Inside Atoms and Molecules
The three laureates share this award in equal parts for their experiments that have produced pulses of light so short that they are measured in attoseconds, thus demonstrating that these pulses can provide images of processes inside atoms and molecules.
Anne L’Huillier’s Overtone Discovery
In 1987, Anne L’Huillier discovered that many different overtones of light arise when transmitting infrared laser light through a noble gas. Each overtone is a light wave with a specific number of cycles for each cycle in the laser light. They occur because the laser light interacts with atoms in the gas, giving some electrons extra energy that they then emit as light. Anne L’Huillier has continued to explore this phenomenon, laying the groundwork for subsequent breakthroughs.
Pierre Agostini’s Attosecond Pulse Breakthrough
In 2001, Pierre Agostini succeeded in producing and investigating a series of consecutive light pulses, with each pulse lasting just 250 attoseconds. At the same time, Ferenc Krausz was working with another type of experiment, one that made it possible to isolate a single light pulse lasting 650 attoseconds.
Enabling Unprecedented Investigations
The laureates’ contributions have enabled the investigation of processes that are so rapid that scientists were previously unable to follow them.
Collaboration and Leadership at ICFO
ICREA Professors at ICFO, Drs. Jens Biegert and Maciej Lewenstein, both lead in this field and collaborate with the laureates both experimentally and theoretically. The 1994 Physical Review A collaboration, noted in the Nobel text, co-authored by Lewenstein, Balcou, Ivanov, L’Huilier, and Corkum, has cited over 5000 times. Similarly, Biegert has made significant contributions through a series of landmark papers in this field, and he has built a world-leading attoscience infrastructure at ICFO, the only one of its kind in Spain. Here, the next generation of attosecond soft x-ray pulses harnesses and applies to advance the frontiers of material physics and chemical imaging.
Contributions of Postdoctoral Researchers
Postdoctoral researchers in the ICFO-Max Plank-Cellex programs over the years, generously funded by Fundación Cellex, have also contributed to the field under the supervision of both ICFO Group Leaders and Prof Ferenc Krausz. Understandably, ICFOnians, fully aware of the significance of this work, have received the news of this year’s award without surprise but with a great deal of enthusiasm.
The Revolutionary Impact of Attosecond Pulses
“Attosecond Pulses of light are a revolutionary tool for basic and applied science since they give us for the first time a camera that is fast enough to acquire crisp images of how and where electrons move,” explains Biegert. “This is important since the motion of electrons determines literally everything, from how a chemical reaction happens, how we metabolize, or how materials and sensors work. Many experimental and theoretical scientists, represented by this year’s laureates, are contributing to this extremely fast-growing new field of science”.
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In a recent study in Nature, an international team of researchers demonstrates theoretically and experimentally the capabilities that solid-state simulators could have in reproducing peculiar states of matter by mimicking electronic behaviour and observing their outcomes. Quantum simulation with excitons
Simple Quantum-Mechanical Models
To describe matter on a microscopic level, physicists rely on very simple quantum-mechanical models. Amongst the most famous of these is the Hubbard model in which quantum particles hop between neighbouring lattice sites, and repel each other when they are at the same site.
Emergence of Macroscopic Behavior
Intriguing macroscopic behaviour can emerge even from this very simple model: if the interaction is dominant, particles tend to isolate on individual sites, and if the number of particles equals the number of sites (or a multiple thereof), the interactions turn the system into an insulating phase known as the Mott state. On the other hand, if the hopping is dominant, particles tend to spread over many sites, giving rise to metallic or even superfluid behaviour (where all atoms form a coherent wavepacket spread over the lattice and forms a non-viscous state of matter).
Extended Interactions and Checkerboard Configuration
More scenarios become possible if interactions act over extended ranges, i. e. particles to repel each other at longer distances. A striking effect of these longer-range interactions is the possibility of stabilization of an insulating phase distinct from the Mott phase, when only half of the sites are occupied. The particles then seek a so-called “checkerboard” configuration in which every second site remains empty on a bipartite periodic structure like a square lattice.
Experimental Observation of Excitonic Phases
For the first time, experimental observations of such a phase of quasi-particles, known as excitons (a bound state of an electron and a hole), have now been witnessed by experimentalists Camille Lagoin and ICFO alumnus François Dubin, from CNRS and Sorbonne Université, in collaboration with theoretical researchers and OPTOlogic partners Utso Bhattacharya, Tobias Grass, Tymoteusz Salamon and ICREA Professor Maciej Lewenstein, from ICFO, Ravindra Chhajlany from Institute of Spintronics and Quantum Information of the Adam Mickiewicz University, and Markus Holzmann from CNRS and Université Grenoble. In their study, the team of researchers have been able to observe this phenomenon by optically exciting a semiconductor sample fabricated in PRISM by Kirk Baldwin and Loren Pfeiffer, from Princeton University. The results have been published in Nature.
Experimental Setup
In this study, a laser pulse injects electrons and holes in two coupled GaAs quantum wells. The spatially-separated and oppositely charged particles then attractively bind together to form a composite particle called an exciton, with an electric dipole moment pointing from the hole to the electron. This dipole moment, through the dipolar forces, makes individual excitons feel each other, even if they are far apart. Additionally, gate electrodes at the surface imprint a square lattice potential for these excitons. These ingredients make the system well represented by a generalized Hubbard model with an extended range of interactions.
Experimental Findings
Cooling down to a temperature of 300 milli-Kelvin (mK) reveals suppressed compressibility of the system, providing evidence of the sought-after insulating phase in the half-filled lattice. Advanced multi-orbital theoretical modeling reveals the presence of the checkerboard pattern. Entering this regime constitutes a well-identified research advancement, where quantum particles spontaneously break the lattice symmetry and arrange themselves into a crystalline structure distinct from the underlying lattice. By tuning the exciton density per site, the experiment also reveals the existence of the incompressible Mott phase at unitary filling. Thus, varying the filling, which serves as a tuning parameter, allows tracing the competition between various insulating phases at finite temperatures.
Potential for Exotic Phases
An important difference between electrons and excitons could allow in the future to reach even more exotic phases: while electrons are so-called fermions (particles that cannot simultaneously occupy the same quantum state according to the Paul exclusion principle) excitons are bosons, and hence can form a condensate, like Cooper pairs of electrons in superconductivity, Helium-4 atoms forming superfluids, or some atomic gases forming Bose Einstein condensates. At very low temperatures, still not attained so far, the three key ingredients: 1) excitons’ ability to condense, 2) the surrounding lattice potential, and 3) the long-range interactions between excitons, may conspire to give rise to a striking “supersolid” phase, in which the constituents would simultaneously show crystalline order (like in a solid) and flow without viscosity (like in a superfluid).
Future Directions and Impact
Thus, the observations achieved by this study highlight the ability of dipolar excitons to enable a controlled environment for the quantum simulation of the “Extended Bose-Hubbard model” at 300 mK. Lowering this temperature to around 10 mK is within experimental reach and an objective for the near future, and will allow the long-coveted lattice supersolids to be expected as a stable phase of matter. By further exploiting the excitons’ orbital and spin degrees of freedom in the lattice, more exotic phases like multi-component supersolids may also be feasible. The experimental achievement attained in this study sets a major step forward and establishes a milestone in research in atomic to condensed matter physics, opening the door to staggering possibilities for the future.
On June 29, 2023, Adrien Cavaillès, representative from the LightOn partner within the consortium of OPTOlogic, was invited to give a presentation at the 2023 Conference on Lasers and Electro-Optics/Europe – European Quantum Electronics Virtual Conferences (CLEO®/Europe-EQEC 2023), which took place from 26 – 30 June 2023, in Munich, Germany.
The CLEO®/Europe-EQEC conference series is an international conference that takes place annually. Furthermore, it seeks to highlight new frontiers in lasers, photonics, and optical science across a wide range of technical areas. by gathering optics and photonics researchers and engineers in Europe. With technical co-sponsorship provided by the European Physical Society (EPS), the IEEE Photonics Society (IPS), and the Optica, CLEO®/Europe not only reflects, but also reinforces, a strong international presence in the complementary research traditions of laser science, photonics, and quantum electronics.
The CLEO®/Europe-EQEC conference series not only provides a unique forum to obtain informative overviews, but also to discuss recent advances in a wide spectrum of topics. These topics not only encompass fundamental light-matter interactions and new sources of coherent light, but also extend to technology development, system engineering, and applications in both industry and applied science.
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Click here to see Adrien’s presentation (PDF)
Link to CLEO®/Europe-EQEC 2023
Adrien Cavaillès presentation CLEO®.
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What is attosecond science, and how is it used?
Optica Fellow Jens Biegert, ICFO, Spain, explains how the field unravels how things work inside materials using ultrashort laser pulses.
If you enjoyed this glimpse into the world of attosecond science, dive deeper into the cutting edge of optics and photonics research on the Optica YouTube channel!
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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