Transregional Collaborative Research Center 183

Entangled States of Matter

Copenhagen – Berlin – Cologne – Weizmann Institute

© Wikimedia Commons

Workshop Rehovot

Weizmann Institute, Israel

25 - 29 March | 2018

© Wikimedia Commons / Bernd Olbertz

Conference Hennef

Sportschule Hennef

07 - 10 June | 2018

Workshops 2017

Miniworkshops

Quantum Machine Learning

25-27 April 2017

Summary

Complex quantum systems may realize entangled states, i.e. superpositions of fundamentally distinct physical states at the same time. For example, where the bits of a classical computer can only assume two mutually exclusive values ‘on’ and ‘off’, a quantum bit can be in a simultaneous superposition of an ‘on’ and an ‘off’ state. As a consequence, a multi-bit ‘quantum computer’ would be able to process information in ways far more powerful than what is classically possible today. Quantum superpositions, however, are highly vulnerable to environmental perturbations such as radiation, noise, or other sources of quantum wave decoherence — the main reason why such type of quantum information processing has not become a reality yet.

The mission of CRC 183 is to overcome these challenges within the context of condensed matter physics. A salient feature of entangled quantum matter is that the large number of atomistic constituents forming a solid may mutually protect each other against the detrimental effects of decoherence. Within CRC 183 we do research on these protective mechanisms, their implications in quantum information theory, and the ensuing perspectives in the design and realization of quantum devices. The long term agenda of the project is to work towards the realization of solid state quantum information devices.

Locations & Organisation

Locations

Freie Universität Berlin

Institut für theoretische Physik

Arminallee 14

14195 Berlin

Germany

Universität zu Köln

Institut für Theoretische Physik

Universität zu Köln

Zülpicher Straße 77

50937 Köln

Germany

Weizmann Institute of Science

Department of Condensed Matter Physics

243 Herzl Street

Rehovot 7610001

Israel

University of Copenhagen

(associated)

Center for Quantum Devices

Universitetsparken 5

2100 Copenhagen

Denmark

Heinrich-Heine-Universität

Institut für Theoretische Physik

40225 Düsseldorf

Germany

Organisation

Spokesperson

Prof. Alexander Altland

Universität zu Köln

Institut für Theoretische Physik

Zülpicher Str. 77a

50937 Köln

Germany

Tel: +49 221 470 4219

Vice-Spokesperson

Prof. Piet Brouwer

Freie Universität Berlin

Institut für theoretische Physik

Arnimallee 14

14195 Berlin

Germany

Tel: +49 30 838 53039

Project Manager

Katrin Krüttgen

Universität zu Köln

Institut für Theoretische Physik

Zülpicher Str. 77

50937 Köln

Phone: +49 221 470 3915

Fax: +49 221 470 5159

Principal Investigators

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Prof. Alexander Altland

A03 Disordered topological matter

C04 Entangled mesoscopic quantum devices

Institut für Theoretische Physik

University of Cologne

Tel: +49-221 - 470 4219

E-Mail: alexal@thp.uni-koeln.de

Dr. Alexander Alldridge

A03 Disordered topological matter

Mathematisches Institut

University of Cologne

Tel: +49-221 - 470 5398

E-Mail: alldridg@math.uni-koeln.de

Dr. Erez Berg

A01 Topology and dynamics

C02 Engineering topological states of matter

Dept. of Condensed Matter Physics,

Weizmann Institute of Science

Tel: +972-8-934-4929

E-Mail: erez.berg@weizmann.ac.il

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Prof. Sebastian Diehl

A02 Gapless topological phases

B02 Topology, dissipation, and quantum memories

Institut für Theoretische Physik

Universität zu Köln

Tel: +49-221 - 470 1056

E-Mail: sebastian.diehl@thp.uni-koeln.de

Prof. Piet Brouwer

A02 Gapless topological phases

A03 Disordered topological matter

Physics Department, Dahlem Center

Freie Universität Berlin

Tel: +49-30 - 838 53039

E-Mail: brouwer@physik.fu-berlin.de

Prof. Reinhold Egger

C01 Measurement and manipulation

of topologicalexcitations

C04 Entangled mesoscopic quantum devices

Institut für Theoretische Physik

Heinrich-Heine-Universität Düsseldorf

Tel: +49-211 - 811 4710

E-Mail: egger@thphy.uni-duesseldorf.de

Prof. Karsten Flensberg

C01 Measurement and Manipulation

of Topological Excitations

C03 Signatures of Majorana bound states

Center for Quantum Devices

Niels Bohr Institute

University of Copenhagen

Tel: +45 25 13 29 69

E-Mail: flensberg@nbi.dk

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Prof. Jens Eisert

B01 Entanglement

B02 Topology, dissipation, and

quantum memories

Physics Department, Dahlem Center

for Complex Quantum Systems

Freie Universität Berlin

Tel: +49-30 - 838 54781

E-Mail: jense@physik.fu-berlin.de

Prof. Yuval Gefen

C01 Measurement and manipulation

of topological excitations

C04 Entangled mesoscopic quantum devices

Department of Condensed Matter

Weizmann Institute of Science

Tel: +972-8-934-4033

E-Mail: yuval.gefen@weizmann.ac.il

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Dr. Maria Hermanns

B03 Theory of Fractionalized

Topological Phases

Institut für Theoretische Physik

Universität zu Köln

Tel: +49-221 - 470 1059

E-Mail: hermanns@thp.uni-koeln.de

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Prof. David Gross

B01 Entanglement

Institute for Theoretical Physics

University of Cologne

Tel: +49-221 - 470 1037

E-Mail: david.gross@thp.uni-koeln.de

Dr. Christoph Karrasch

A01 Topology and dynamics

Physics Department, Dahlem Center

for Complex Quantum Systems

Freie Universität Berlin

E-Mail: c.karrasch@fu-berlin.de

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Dr. Karen Michaeli

C03 Signatures of Majorana bound states

Dept. of Condensed Matter Physics,

Weizmann Institute of Science

Tel: +972-8-934-6515

E-Mail: karen.michaeli@weizmann.ac.il

Prof. Charles M. Marcus

C02 Engineering Topological States of Matter

C03 Signatures of Majorana bound states

Center for Quantum Devices

Niels Bohr Institute

University of Copenhagen

Tel: +45 20 34 11 81

E-Mail: marcus@nbi.dk

Prof. Yuval Oreg

B03 Theory of fractionalized topological

phases

C02 Engineering topological states of matter

Dept. of Condensed Matter Physics

Weizmann Institute of Science

Tel: +972-8-934-4573

E-Mail: Yuval.Oreg@weizmann.ac.il

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Prof. Mark Rudner

A01 Topology and dynamics

B02 Topology, dissipation, and quantum memories

Niels Bohr International Academy

Niels Bohr Institute

Tel: +45 91105803

E-Mail: rudner@nbi.ku.d

Prof. Achim Rosch

A01 Topology and dynamics

Institute for Theoretical Physics

University of Cologne

Tel: +49-221 - 470 4994

E-Mail: rosch@thp.uni-koeln.de

Prof. Johannes Reuther

A02 Gapless topological phases

Physics Department, Dahlem Center

for Complex Quantum Systems

Freie Universität Berlin

Tel: +49-30 - 838 52781

E-Mail: johannes.reuther@fu-berlin.de

Prof. Simon Trebst

B01 Entanglement

Institute for Theoretical Physics

University of Cologne

Tel: +49-221 - 470 7420

E-Mail: trebst@thp.uni-koeln.de

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Prof. Adiel (Ady) Stern

B03 Theory of fractionalized topological

phases

Dept. of Condensed Matter Physics

Weizmann Institute of Science

Tel: +972-8-934-2502

E-Mail: adiel.stern@weizmann.ac.il

Prof. Felix von Oppen

C02 Engineering topological states

of matter

Physics Department, Dahlem Center

for Complex Quantum Systems

Freie Universität Berlin

Tel: +49-30 - 838 53036

E-Mail: vonoppen@physik.fu-berlin.de

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Prof. Martin R. Zirnbauer

A03 Disordered topological matter

Institut für Theoretische Physik

Universität zu Köln

Tel: +49-221 - 470 4302

E-Mail: zirnbauer@uni-koeln.de

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© Charlie Marcus

Physics of topological excitations

Projects A

Project A01: Topology and dynamics

The project investigates how topological states and excitations can be created and manipulated in environments with externally imposed time dependence.

This will include periodic modulations for which novel phases of topological matter can emerge. Another branch of the project explores how topological excitations forming at the interfaces between distinct topological phases – the most elementary states utilized by quantum information protocols – respond to dynamical processes involved in any braiding protocol.

Project A02: Gapless topological phases

Initially, research on topological matter focused on gapped phases, such as topological insulators or superconductors. Project A02 Gapless topological matter considers the more recent extensions of the topology paradigm to the strongly spin-orbit entangled gapless Weyl metal and semimetal phases. A second line of activity aims at classifying the fractionalized excitations ("spinons") of strongly entangled spin liquids. A special case is the "Weyl spin liquid", in which the spinons have a dispersion relation similar to that of the Weyl semimetals.

Project A03: Disordered topological matter

Project A03 focuses on the surprisingly rich interplay of topological order with the static disorder inevitably present in any realistic condensed matter system. The project explores the integrity of the topological phases of insulators and metals, including topological phases protected by discrete symmetries that are broken by the disorder. It also contains a more fundamental line of activity, aiming at the construction of a mathematically rigorous classification of non-translationally invariant topological matter.

Entanglement and information

Projects B

Projects C

Project B01: Entanglement

Project B01 will further the conceptual understanding of entanglement in the context of topological order. We seek analytic, numerical, and experimental methods for quantifying entanglement in fermionic and bosonic many-body systems. Tensor networks feature strongly as a tool to capture the intricate correlations in states of quantum many-body systems and in the classification of phases in two dimensions. Using computational complexity theory, we aim to identify “computational phases”, by linking the potential utility of states in quantum computation protocols to their topological properties.

Project B02: Topology, dissipation, and quantum memories

The goal of this project is the investigation of the subtle interplay between dissipation and topology. Dissipative processes result from the interaction of a system's degrees of freedom with their environment. They typically act as undesired perturbations. However, if properly designed, they need not counteract mechanical correlations, but can even create them. The emphasis of this research is the targeted use of suitably tailored dissipative processes to prepare topologically non-trivial states in a robust manner. In this way, important applications for quantum information, such as the creation of quantum memories, will be enabled.

Project B03: Theory of fractionalized topological phases

While noninteracting topological phases are by now well understood, we are only on the verge of understanding the wealth of fractionalized topological phases, in which interactions stabilize novel types of long-range entanglement. The focus of project B03 is to explore experimentally feasible manifestations of such phases and in particular to search for fractionalized quasiparticles whose non-abelian exchange statistics goes beyond those of Majorana fermions. These may for instance occur in coupled-wire systems or in quantum Hall liquids in the second Landau level.

Design and functionality of entangled quantum device

Project C01: Measurement and manipulation of topological excitations

This project explores the influence of measurement processes on entangled states of matter. We will design minimally invasive measurement protocols employing tailor-made mesoscopic systems as detectors. Such protocols allow for the generation, detection and manipulation of entangled states in systems hosting topological excitations. After these concepts have been implemented for the comparatively basic case of Majorana bound states, we will turn towards more complex parafermion excitations.

Project C02: Engineering topological states of matter

Project C02 will pursue the construction of entangled topological states of matter made from hybrids of well-understood building blocks. A paradigmatic example for the success of such an approach comes from the engineering of topological superconductors and Majorana bound states. This project aims at broadening both the materials base for engineering such phases and the classes of accessible topological phases. We will advance platforms for universal topological quantum computation exploiting the proximity coupling of superconductors and quantum Hall systems.

Project C03: Signatures of Majorana bound states

Project C03 will study topological superconductivity based on hybrids of conventional superconductors and semiconductors. This platform is quite advanced experimentally and has already allowed to establish the existence of Majorana bound states. The next step is to demonstrate their nonlocal fusion and nonabelian braiding properties. In a symbiosis with experimental efforts of the Marcus group, we will propose and study further signatures of Majorana bound states, explore schemes to benchmark, control, and read out an elementary topological qubit, and develop strategies for implementing Majorana braiding operations.

Project C04: Entangled mesoscopic quantum devices

This project focuses on the hierarchical construction of strongly entangled quantum devices. We start from small building blocks representing either (i) an effective large spin formed on a quantum dot, or (ii) the fermionic zero mode in a mesoscopic topological superconductor hosting four Majorana bound states. We will study entanglement between a single block and attached leads, as well as entanglement generated in assemblies of blocks all the way to two-dimensional lattices thereof. We will propose new Majorana-based quantum computation schemes as well as meta-materials based on entangled large spins.

Workshop Berlin

Magnus-Haus Berlin

23 - 25 November | 2017

Workshop Rehovot

Weizmann Institute of Science

25 - 29 March | 2018

Contact

University of Cologne

SPOKESPERSON

Universität zu Köln

Institut für Theoretische Physik

Zülpicher Str. 77a

50937 Köln

Germany

Phone: +49 221 470 4219

Mail: alexal@thp.uni-koeln.de

PROJECT MANAGER

Katrin Krüttgen

Universität zu Köln

Institut für Theoretische Physik

Zülpicher Str. 77

50937 Köln

Germany

Phone: +49 221 470 3915

Fax: +49 221 470 5159

Mail: kk@thp.uni-koeln.de

University of Copenhagen

Niels Bohr Institute

University of Copenhagen

H. C. Ørsted Institute (Building 3)

Universitetsparken 5

2100 Copenhagen Ø

Denmark

Phone: +45 20 34 11 81

E-Mail: marcus@nbi.dk

Freie Universität Berlin

Dahlem Center for Complex Quantum Systems

Freie Universität Berlin

Arnimallee 14

D-14195 Berlin

Germany

Phone: +49-30-838 55248

Fax: +49-30-838 55258

Weizmann Institute of Science

Department of Condensed Matter Physics

Rehovot 7610001

Israel

Phone: +972-8-9343897

Fax +972-8-9344477

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