We study new phenomena arising at the interface of out-of-equilibrium dynamics, quantum many-body physics, and topology. Particular emphasis will be given to the possible realization of these ideas on present-day digital and analogue “quantum simulators”.  We will develop protocols to create low-energy states of arbitrary Hamiltonians on these quantum simulators, investigate new ways to classify, control and manipulate anomalous topological excitations in periodically driven systems,
and explore topological pumping in edge states of spin-Hall insulator.

Brouwer | Rosch | Berg

Project A02 considers the topology paradigm in the strongly spin-orbit entangled gapless phases such as Weyl or nodal-line semimetals. It encompasses abstract theoretical questions concerning the classification of such phases with theoretical studies of transport properties and combined theoretical/ experimental studies of boundary signatures of the nontrivial topology. A particular emphasis is placed on Weyl semimetals with spatial inhomogeneities, which enter a phase in which phenomena normally associated with the boundary dominate the bulk.

Breitkreiz | Brouwer | Beidenkopf | Yan

Project A03 addresses the physics of correlations, entanglement, and topology in systems subject to randomness. The project now includes four lines of activity: disorder in strongly correlated finite size systems as relevant to, e.g., NISQ era quantum computing architectures, disorder in tensor networks, the characterization of topological quantum matter in the combined presence of symmetries and translational invariance breaking, and disorder and chaos in holographic quantum matter. Project A03 continues to be a meta project in that its research themes resonate with many others in the CRC where translational symmetry breaking is a natural step towards added realism.

Brouwer | Eisert | Altland

Project A04 studies quantum states of electrons whose entanglement over long distances permits excitations with microscopically forbidden fractional quantum numbers. Our ultimate goal is to materialize these exotic states in natural or synthetic frustrated magnets and quantum-Hall platforms. We will combine field theory, functional renormalization group, and tensor-network methods to determine conditions favoring quantum spin liquids without requiring unphysical symmetries or interactions. Additionally, our experimental-theoretical collaboration on superconductor-fractional quantum Hall hybrid systems will provide vital insights and tools towards realizing non-Abelian quasiparticles beyond Majorana modes.

Reuther | Rizzi | Mross | Ronen

Project B01 aims to enhance the understanding of entanglement, in particular the dynamics of entanglement, and to facilitate the transition from classifying entangled states to purposefully engineering and manipulating them. An instrumental platform for this task are quantum circuits, which cover many aspects of a general quantum mechanical evolution and will serve as a bridge between theoretical concepts and experimental reality in NISQ devices. Through further integration of machine learning concepts, the project seeks to efficiently engineer entangled quantum states and to utilize shallow quantum circuits for learning tasks. In essence, quantum circuits play a pivotal role, serving as the foundational structure for this entanglement project within the CRC.

Eisert | Buchhold | Trebst | Turkeshi

This project is committed to shaping the theory of driven open quantum matter, characterized by an interplay of unitary dynamics, dissipation and decoherence, and measurements. It is realized, for example, in noisy intermediate scale quantum platforms. On the one hand, this comprises establishing concepts for manipulation, steering and diagnostics of such systems. On the other hand, we aim at an understanding of fundamental questions such as the nature and observability of measurement induced phase transitions, or the robustness of quantum information in many-body systems.

Koch | Diehl | Egger | Pappalardi

Holography provides us with novel avenues to understanding the physics of quantum information and entanglement, based on principles of geometry. Project B04 combines the holographic principle with synthetic approaches to quantum matter. We will define and explore quantum systems and their holographic bulk duals by a combination of complementary design concepts, including the coupling of strongly interacting mesoscopic quantum systems, tensor networks, and field theoretical methods. The long term goal is to understand the physics of entanglement from a novel perspective and, conversely, to unlock holographic dualities building on principles of quantum information. 

Eisert | Altland | Bagrets | Callebaut

In this project, we propose and study measurement protocols for generating and manipulating entanglement in several types of quantum devices. In particular, we will formulate practically useful protocols for measurement-induced phase transition scenarios in actively monitored quantum circuits. A closely related goal is to study passive and active steering protocols for monitored circuits composed of Andreev spin qubits and transmon qubits. Such circuits may allow for the preparation, stabilization, and manipulation of highly entangled states.

Flensberg | Marcus | Egger | Diehl

Project C02 will pursue novel concepts to design and probe entangled topological states of matter. The focus of the project will be to explore correlated and topological electron physics in novel graphene-based structures, including twisted bilayer graphene. An important part of the project will revolve around the quantum twisting microscope and its potential for probing collective excitations such as phonons as well the symmetry of the superconducting order parameter. This line of research will be based on a collaboration between theory and experiment. 

v. Oppen | Berg | Ilani | Oreg

Project C03 will study hybrid platforms which have been much investigated in recent years in the context of topological superconductivity. We will explore novel phenomena in such platforms, including semiconductor-superconductor hybrid wires as well as magnetic adatoms on superconductors. Work on semiconductor-superconductor systems will focus on developing tripartite wires including epitaxial ferromagnets as well a new generation of Josephson junction arrays. Work on magnetic adatoms on superconductors will explore two-dimensional arrays of adatoms built by manipulation with a scanning tunneling microscope tip. This will be complemented by studies of fractional Chern insulators, which may hold much promise when forming hybrids with superconductors. 

Franke | v. Oppen | Vaitiekenas | Stern

Coupled superconducting circuits have emerged as one of the leading platforms in quantum information science. Their hallmark, the nonlinearity of Josephson junctions, enables the definition of the qubit subspace in the first place but may also give rise to many-body quantum chaos. We will carry our investigation of spectral instabilities caused by the nonlinearities over to flux and fluxonium qubits. We will seek ways to detect and mitigate dynamical instabilities during gate operations but also explore nonlinearities as a resource for error protection.

Koch | Flensberg | Altland | Trebst