Highlights

Institute's News

MPI-PKS launches virtual workshop jointly with ICTP

In times of severe travel constraints or even lockdowns, MPI-PKS is determined to provide opportunities for scientists to meet, now remotely. As a pilot event, we are launching a two-day virtual workshop jointly with ICTP in Trieste, focusing on Real-time Dynamics in Strongly correlated Quantum Matter.
Publication Highlights

Hierarchy of Relaxation Timescales in Local Random Liouvillians

To characterize the generic behavior of open quantum systems, we consider random, purely dissipative Liouvillians with a notion of locality. We find that the positivity of the map implies a sharp separation of the relaxation timescales according to the locality of observables. Specifically, we analyze a spin-1/2 system of size $\ell$ with up to $n$-body Lindblad operators, which are $n$ local in the complexity-theory sense. Without locality ($n=\ell$), the complex Liouvillian spectrum densely covers a “lemon”-shaped support. However, for local Liouvillians ($n<\ell$), we find that the spectrum is composed of several dense clusters with random matrix spacing statistics, each featuring a lemon-shaped support wherein all eigenvectors correspond to $n$-body decay modes. This implies a hierarchy of relaxation timescales of n-body observables, which we verify to be robust in the thermodynamic limit. Our findings for n locality generalize immediately to the case of spatial locality, introducing further splitting of timescales due to the additional structure.

Wang et al., Phys. Rev. Lett. 124, 100604 (2020)
Awards and Honors

Dresden Excellence Award 2019

Stadt Dresden zeichnet zum dritten Mal herausragende Abschlussarbeiten mit dem Wissenschaftspreis aus.

Am Sonnabend, 29. Februar 2020, vergibt die Landeshauptstadt Dresden gemeinsam mit dem Netzwerk „Dresden – Stadt der Wissenschaften“ den mit 30 000 Euro dotierten DRESDEN EXCELLENCE AWARD. „Mit dem Wissenschaftspreis der Stadt Dresden zeichnen wir als Stadtverwaltung zum dritten Mal in Folge vier Absolventinnen und Absolventen Dresdner Hochschulen für ihre hervorragenden wissenschaftlichen Abschlussarbeiten aus. Diese Würdigung stärkt die Wahrnehmung Dresdens als exzellenten Wissenschaftsstandort“, sagt Oberbürgermeister Dirk Hilbert, der zugleich als Vorsitzender der Jury wirkte.
Ausgezeichnet werden in jedem Jahr vier eingereichte Arbeiten, die besondere Relevanz und Zukunftsorientierung für die Dresdner Stadtentwicklung und Stadtgesellschaft vorweisen.
Die mit 12 000 Euro dotierte Auszeichnung in der Kategorie Habilitation geht an Dr. habil. Sebastian Wüster für seine Habilitationsschrift „Quantentransport in ultrakalten Rydberg Aggregaten“. Die Forschung in der theoretischen Physik untersucht die Anwendung von kalten Rydberg Aggregaten auf in der Quantensimulation relevante Transportprozesse. Dr. Wüster publizierte im Rahmen seiner Habilitation 15 wissenschaftliche Arbeiten, darunter einen Review Artikel und sechs Physical Review Letters. Mit dieser Leistung wird Dr. Wüster als internationaler Experte ultrakalter Rydbergphysik wahrgenommen und ist zunächst auf eine Assistenzprofessur in Ankara/Türkei und schließlich als Assoziierter Professor an das Indian Institute for Science, Education and Research Bhopal/Indien berufen worden. Damit setzt Dr. Wüster nun mit seiner eigenen Forschungsgruppe international die Dresdner Forschung in der theoretischen Physik auf höchstem wissenschaftlichen Niveau fort.
Publication Highlights

"Census" in the zebrafish's brain

Dresden scientists explore newborn, regenerated neurons The zebrafish is a master of regeneration: If brain cells are lost due to injury or disease, it can simply reproduce them - contrary to humans where this only happens in the fetal stage. However, the zebrafish is evolutionarily related to humans and, thus, possesses the same brain cell types as humans. Can a hidden regeneration potential also be activated in humans? Are therapies for stroke, craniocerebral trauma and presently incurable diseases such as Alzheimer's and Parkinson's possible?
Dresden scientists have now succeeded in determining the number and type of newly formed neurons in zebrafish; practically conducting a “census” in their brains. Following an injury, zebrafish form new neurons in high numbers and integrate them into the nervous system, which is the reason for their amazing brain regeneration ability. The study is a true collaboration project “made in Dresden”: Scientists from the Center for Regenerative Therapies TU Dresden (CRTD) combined their expertise in stem cell biology with complex bio-informatic analyses from the Max Planck Institute for the Physics of Complex Systems (MPI-PKS) and the Center for Systems Biology Dresden (CSBD) and with the latest sequencing methods from the DRESDEN-concept Genome Center.
For their study now published in Development, the team led by Christian Lange and Michael Brand from the CRTD used adult transgenic zebrafish in whose forebrain they were able to identify the newborn neurons. The forebrain of the zebrafish is the equivalent to the human cerebral cortex, the largest and functionally most important part of the brain. Together with the Steffen Rulands group at the MPI-PKS and the CSBD, the interdisciplinary research team investigated the newborn and mature neurons as well as brain stem cells using single cell sequencing. Thus, they discovered specific markers for newborn neurons and were able to comprehensively analyze which types of neurons are newly formed in the adult brain of the zebrafish. Together, researchers also investigated the data obtained from brain cells of mice and found that zebrafish and mice have the same cell types. This also makes these results highly relevant for humans.
"On the basis of this study, we will further investigate the regeneration processes that take place in zebrafish. In particular, we will study the formation of new neurons after traumatic brain damage and their integration," explains Michael Brand, CRTD Director and senior author of the study. "We hope to gain insights that are relevant for possible therapies helping people after injuries and strokes or suffering from neurodegenerative diseases. We already know that a certain regenerative ability is also present in humans and we are working on awakening this potential. The results of our study are also important for understanding the conditions under which transplanted neurons can network with the existing ones and thus could let humans re-gain their former mental performance.”
Original Publication: Christian Lange, Fabian Rost, Anja Machate, Susanne Reinhardt, Matthias Lesche, Anke Weber, Veronika Kuscha, Andreas Dahl, Steffen Rulands and Michael Brand: „Single cell sequencing of radial glia progeny reveals diversity of newborn neurons in the adult zebrafish brain”
Development 20 147, published 9 January 2020, doi: 10.1242/dev.185595
Awards and Honors

Physik-Preis Dresden

Am 14. Januar 2020 wird der Physik-Preis Dresden des Max-Planck-Instituts für Physik komplexer Systeme (MPI-PKS) und der TU Dresden an Dr. Adam Nahum von der Oxford University vergeben. Die Preisverleihung findet ab 16 Uhr im Rahmen eines Festkolloquiums im Recknagel-Bau der TU Dresden statt. Adam Nahum hat in seiner noch jungen wissenschaftlichen Laufbahn bereits eine Reihe exzellenter und vielbeachteter Beiträge geleistet. Besonders kennzeichnend für ihn ist seine herausragende Fähigkeit, Konzepte aus verschiedenen Bereichen der theoretischen Physik zu einem universellen Verständnis des Verhaltens komplexer Systeme zu verbinden und so tiefe Einsichten zu erhalten. „Die Originalität seiner Ansätze und die außergewöhnliche Vielfalt seiner Forschungsthemen, verkörpern in idealer Weise den Grundgedanken des Physik-Preises Dresden,“ begründet Prof. Walter Strunz, Vorsitzender des Preiskomitees, die Entscheidung für Adam Nahum. Verankert in dem Grundgedanken „Die Zukunft gehört denjenigen, die zusammen arbeiten“ ist es das Ziel des Preises, gerade solche herausragenden Forscherinnen und Forscher auszuzeichnen, an deren Arbeiten beide DRESDEN-concept-Partner MPI-PKS und TU Dresden besonders interessiert sind. An Nahums Forschungsgebieten, darunter Quantenvielteilchenphysik, Nichtgleichgewicht oder Quantenchaos arbeiten verschiedene Gruppen der TU Dresden und des MPI-PKS. Viele der Dresdner Physiker freuen sich daher auf den einwöchigen Aufenthalt des Preisträgers, der weitere Fachvorträge und vor allem viel Raum für Diskussionen mit sich bringt. Der Preisträger Adam Nahum Adam Nahum hat in Oxford und Chicago Physik und Philosophie studiert und 2013 an der Universität Oxford über kritische Phänomene in Schleifen-Modellen promoviert. Nach einer Postdoc-Phase am Massachusetts Institute of Technology (MIT) ist er seit 2017 wieder an der Oxford University.
Publication Highlights

Phasonic Spectroscopy of a Quantum Gas in a Quasicrystalline Lattice

Phasonic degrees of freedom are unique to quasiperiodic structures and play a central role in poorly understood properties of quasicrystals from excitation spectra to wave function statistics to electronic transport. However, phasons are challenging to access dynamically in the solid state due to their complex long-range character and the effects of disorder and strain. We report phasonic spectroscopy of a quantum gas in a one-dimensional quasicrystalline optical lattice. We observe that strong phasonic driving produces a nonperturbative high-harmonic plateau strikingly different from the effects of standard dipolar driving. Tuning the potential from crystalline to quasicrystalline, we identify spectroscopic signatures of quasiperiodicity and interactions and map the emergence of a multifractal energy spectrum, opening a path to direct imaging of the Hofstadter butterfly.

S.V. Rajagopal et al., Phys. Rev. Lett. 123, 223201 (2019)
Publication Highlights

Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase Transitions

The discovery of quasicrystals with crystallographically forbidden rotational symmetries has changed the notion of the ordering in materials, yet little is known about the dynamical emergence of such exotic forms of order. Here we theoretically study a nonequilibrium cavity-QED setup realizing a zero-temperature quantum phase transition from a homogeneous Bose-Einstein condensate to a quasicrystalline phase via collective superradiant light scattering. Across the superradiant phase transition, collective light scattering creates a dynamical, quasicrystalline optical potential for the atoms. Remarkably, the quasicrystalline potential is “emergent” as its eightfold rotational symmetry is not present in the Hamiltonian of the system, rather appears solely in the low-energy states. For sufficiently strong two-body contact interactions between atoms, a quasicrystalline order is stabilized in the system, while for weakly interacting atoms the condensate is localized in one or few of the deepest minima of the quasicrystalline potential.

F. Mivehvar et al., Phys. Rev. Lett. 123, 210604 (2019)
Publication Highlights

Quantifying and Controlling Prethermal Nonergodicity in Interacting Floquet Matter

Periodic driving has become a key element in the experimental efforts to synthesize interesting many-body quantum states. Importantly, this depends crucially on the existence of a prethermal regime, which exhibits drive-tunable properties while forestalling the effects of undesirable heating. This dependence motivates the search for direct experimental probes of the underlying localized nonergodic nature of the wave function in this metastable regime. We report experiments on a many-body Floquet system consisting of atoms in an optical lattice subjected to ultrastrong sign-changing amplitude modulation. In this work, we measure an inverse participation ratio quantifying the degree of prethermal localization of the many-body wave function as a function of tunable drive parameters and interactions. We obtain a complete prethermal map of the drive-dependent properties of Floquet matter spanning four square decades of parameter space. Following the full time evolution, we observe sequential formation of two prethermal plateaux, interaction-driven ergodicity, and strongly frequency-dependent dynamics of long-time thermalization. The quantitative characterization of the prethermal Floquet matter realized in these experiments, along with the demonstration of control of its properties by variation of drive parameters and interactions, opens a new frontier for probing far-from-equilibrium quantum statistical mechanics and new possibilities for dynamical quantum engineering.

Singh et al., Phys. Rev. X 9, 041021 (2019)
Publication Highlights

Cavity-Quantum-Electrodynamical Toolbox for Quantum Magnetism

The recent experimental observation of spinor self-ordering of ultracold atoms in optical resonators has set the stage for the exploration of emergent magnetic orders in quantum-gas-cavity systems. Based on this platform, we introduce a generic scheme for the implementation of long-range quantum spin Hamiltonians composed of various types of couplings, including Heisenberg and Dzyaloshinskii-Moriya interactions. Our model is composed of an effective two-component Bose-Einstein condensate, driven by two classical pump lasers and coupled to a single dynamic mode of a linear cavity in a double $\Lambda$ scheme. Cavity photons mediate the long-range spin-spin interactions with spatially modulated coupling coefficients, where the latter ones can be tuned by modifying spatial profiles of the pump lasers. As experimentally relevant examples, we demonstrate that by properly choosing the spatial profiles of the pump lasers achiral domain-wall antiferromagnetic and chiral spin-spiral orders emerge beyond critical laser strengths. The transition between these two phases can be observed in a single experimental setup by tuning the reflectivity of a mirror. We also discuss extensions of our scheme for the implementation of other classes of spin Hamiltonians.

F. Mivehvar et al., Phys. Rev. Lett. 122, 113603 (2019)