From The Dresden University of Technology [Technische Universität Dresden] (DE) And The Technical University of Munich [Technische Universität München] (DE): “New Fur for the Quantum Cat. Quantum materials:: entanglement of many atoms discovered for the first time”

From The Dresden University of Technology [Technische Universität Dresden] (DE)

And

The Technical University of Munich [Technische Universität München] (DE)

9.2.22
Prof. Matthias Vojta
Technische Universität Dresden
Chair of Theoretical Solid State Physics
Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter
Co-spokesperson
Tel.: +49 351 463-34135
Matthias.Vojta@tu-dresden.de

Schroedinger’s cat with quantum fur: In the material LiHoF4, physicists from the universities of Dresden and Munich have discovered a new quantum phase transition at which the domains behave in a quantum mechanical fashion. Credit: C. Hohmann, MCQST.

Be it magnets or superconductors: materials are known for their various properties. However, these properties may change spontaneously under extreme conditions. Researchers at the Technische Universität Dresden (TUD) and the Technische Universität München (TUM) have discovered an entirely new type of such phase transitions. They display the phenomenon of quantum entanglement involving many atoms, which previously has only been observed in the realm of few atoms. The results were recently published in the scientific journal Nature [below].

New Fur for the Quantum Cat

In physics, Schroedinger’s cat is an allegory for two of the most awe-inspiring effects of quantum mechanics: entanglement and superposition. Researchers from Dresden and Munich have now observed these behaviors on a much larger scale than that of the smallest of particles. Until now, materials that display properties like, e.g., magnetism have been known to have so-called domains – islands in which the materials properties are homogeneously either of one or a different kind (imagine them being either black or white, for example). Looking at lithium holmium fluoride (LiHoF4), the physicists have now discovered a completely new phase transition, at which the domains surprisingly exhibit quantum mechanical features, resulting in their properties becoming entangled (being black and white at the same time). “Our quantum cat now has a new fur because we’ve discovered a new quantum phase transition in LiHoF4 which has not previously been known to exist,” comments Matthias Vojta, Chair of Theoretical Solid State Physics at TUD.

Phase transitions and entanglement

We can easily observe the spontaneously changing properties of a substance if we look at water: at 100 degrees Celsius it evaporates into a gas, at zero degrees Celsius it freezes into ice. In both cases, these new states of matter form as a consequence of a phase transition where the water molecules rearrange themselves, thus changing the characteristics of the matter. Properties like magnetism or superconductivity emerge as a result of electrons undergoing phase transitions in crystals. For phase transitions at temperatures approaching the absolute zero at -273.15 degrees Celsius, quantum mechanical effects such as entanglement come into play, and one speaks of quantum phase transitions. “Even though there are more than 30 years of extensive research dedicated to phase transitions in quantum materials, we had previously assumed that the phenomenon of entanglement played a role only on a microscopic scale, where it involves only a few atoms at a time,” explains Christian Pfleiderer, Professor of Topology of Correlated Systems at the TUM.

Quantum entanglement is one of the most astonishing phenomena of physics, where the entangled quantum particles exist in a shared superposition state that allows for usually mutually exclusive properties (e.g., black and white) to occur simultaneously. As a rule, the laws of quantum mechanics only apply to microscopic particles. The research teams from Munich and Dresden have now succeeded in observing effects of quantum entanglement on a much larger scale, that of thousands of atoms. For this, they have chosen to work with the well-known compound LiHoF4.

Spherical samples enable precision measurements

At very low temperatures, LiHoF4 acts as a ferromagnet where all magnetic moments spontaneously point in the same direction. If you then apply a magnetic field exactly vertically to the preferred magnetic direction, the magnetic moments will change direction, which is known as fluctuations. The higher the magnetic field strength, the stronger these fluctuations become, until, eventually, the ferromagnetism disappears completely at a quantum phase transition. This leads to the entanglement of neighboring magnetic moments. “If you hold up a LiHoF4 sample to a very strong magnet, it suddenly ceases to be spontaneously magnetic. This has been known for 25 years,” summarizes Vojta.

What is new is what happens when you change the direction of the magnetic field. “We discovered that the quantum phase transition continues to occur, whereas it had previously been believed that even the smallest tilt of the magnetic field would immediately suppress it,” explains Pfleiderer. Under these conditions, however, it is not individual magnetic moments but rather extensive magnetic areas, so-called ferromagnetic domains, that undergo these quantum phase transitions. The domains constitute entire islands of magnetic moments pointing in the same direction. “We have used spherical samples for our precision measurements. That is what enabled us to precisely study the behavior upon small changes in the direction of the magnetic field,” adds Andreas Wendl, who conducted the experiments as part of his doctoral dissertation.

From fundamental physics to applications

“We have discovered an entirely new type of quantum phase transitions where entanglement takes place on the scale of many thousands of atoms instead of just in the microcosm of only a few,” explains Vojta. “If you imagine the magnetic domains as a black-and-white pattern, the new phase transition leads to either the white or the black areas becoming infinitesimally small, i.e., creating a quantum pattern, bevor dissolving completely.” A newly developed theoretical model successfully explains the data obtained from the experiments. “For our analysis, we generalized existing microscopic models and also took into account the feedback of the large ferromagnetic domains to the microscopic properties,” elaborates Heike Eisenlohr, who performed the calculations as part of her PhD thesis.

The discovery of the new quantum phase transitions is important as a foundation and general frame of reference for the research of quantum phenomena in materials, as well as for new applications. “Quantum entanglement is applied and used in technologies like quantum sensors and quantum computers, amongst other things,” says Vojta. Pfleiderer adds: “Our work is in the area of fundamental research, which, however, can have a direct impact on the development of practical applications, if you use the materials properties in a controlled way.”

Science paper:
Nature

See the full article here.

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The Technical University of Munich [Technische Universität München] (DE) is a public research university in Munich, with additional campuses in Garching, Freising, Heilbronn, Straubing, and Singapore. A technical university that specializes in engineering, technology, medicine, and the applied and natural sciences, it is organized into 11 schools and departments, and supported by numerous research centers.

A University of Excellence under the German Universities Excellence Initiative, TUM is consistently ranked among the leading universities in the European Union and its researchers and alumni include 16 Nobel laureates and 23 Leibniz Prize winners.

Departments

Aerospace engineering, geodesy
Ottobrunn

Department of Architecture
Munich

Department of Civil, Geo and Environmental Engineering
Civil engineering, environmental engineering, earth science
Munich

Department of Chemistry
Garching

Department of Electrical and Computer Engineering
Munich

Department of Informatics [Computer science]
Garching

Department of Mechanical Engineering
Garching

Department of Mathematics
Garching

School of Medicine
Munich

Department of Physics
Garching

Department of Sport and Health Sciences
Munich

School of Education
Munich

School of Governance
Munich

School of Management
Munich

School of Life Sciences
Freising

Research

The Technical University of Munich is one of the most research-focused universities in Europe. This claim is supported by relevant rankings, such as the funding ranking of the German Research Foundation and the research ranking of the Centre for Higher Education.

Under the German Universities Excellence Initiative, TUM has obtained funding for multiple research clusters, including e-conversion (energy technology), MCQST – Munich Center for Quantum Science and Technology(DE) (quantum mechanics), ORIGINS (astrophysics, biophysics and particle physics), and SYNERGY (neurology).

In addition to the schools and departments, TUM has set up numerous research centers with external cooperation partners.

Integrative research centers (IRCs) combine research with teaching. They include the TUM Institute for Advanced Study (TUM-IAS), the TUM-Munich Center for Technology in Society (MCTS), TUM-Munich Data Science Institute (MDSI), TUM-Munich School of Engineering , TUM-Munich Institute of Biomedical Engineering, and the TUM-Munich Institute of Robotics and Machine Intelligence.

Corporate research centers (CRCs) carry out research independently of the schools and departments, cooperating with industry partners for application-driven research. They include the research reactor FRM II, the Center for Functional Protein Assemblies (CPA), the Catalysis Research Center (CRC), the center for translational Cancer Research (TranslaTUM), the Walter Schottky Institute (WSI), the Hans Eisenmann-Zentrum for Agricultural Science, and the Institute for Food & Health (ZIEL).

Rankings

TUM is ranked first in Germany in the fields of engineering and computer science, and within the top three in the natural sciences.

In the QS World Rankings, TUM is ranked 19th (worldwide) in engineering and technology, 28th in the natural sciences, 29th in computer science, and 50th place overall. It is the highest ranked German university in those subject areas.

In the Times Higher Education World University Rankings, TUM stands at 38th place worldwide and 2nd place nationwide. Worldwide, it ranks 14th in computer science, 22nd in engineering and technology, and 23rd in the physical sciences. It is the highest ranked German university in those subject areas.

In the Academic Ranking of World Universities, TUM is ranked at 52nd place in the world and 2nd place in Germany. In the subject areas of computer science and engineering, electrical engineering, aerospace engineering, food science, biotechnology, and chemistry, TUM is ranked first in Germany.

In the 2021 Global University Employability Ranking of the Times Higher Education World Rankings, TUM was ranked 13th in the world and 4th in Europe. TUM is ranked 7th overall in Reuters’ 2019 European Most Innovative University ranking.

The TUM School of Management is triple accredited by the European Quality Improvement System (EQUIS), the Association to Advance Collegiate Schools of Business (AACSB) and the Association of MBAs (AMBA).

Partnerships

TUM has over 160 international partnerships, ranging from joint research activities to international study programs. Partners include:

Europe: ETH Zurich, EPFL, ENSEA, École Centrale Paris, TU Eindhoven, Technical University of Denmark, and Technical University of Vienna
United States:The Massachusetts Institute of Technology , Stanford University, Northwestern University, University of Illinois, Cornell University, University of Texas-Austin, and Georgia Tech
Asia: The National University of Singapore, Multimedia University, Hong Kong University of Science and Technology, Huazhong University of Science and Technology, Tsinghua University, University of Tokyo, Indian Institute of Technology Delhi, Amrita University, and Sirindhorn International Institute of Technology.
Australia: Australian National University, University of Melbourne, The Royal Melbourne Institute of Technology (AU).

Through the Erasmus+ program and its international student exchange program TUMexchange, TUM students are provided by opportunities to study abroad.e, TUM students are provided by opportunities to study abroad.

The Dresden University of Technology [Technische Universität Dresden] (DE) is a public research university, the largest institute of higher education in the city of Dresden, the largest university in Saxony and one of the 10 largest universities in Germany with 32,389 students as of 2018.

The name Technische Universität Dresden has only been used since 1961; the history of the university, however, goes back nearly 200 years to 1828. This makes it one of the oldest colleges of technology in Germany, and one of the country’s oldest universities, which in German today refers to institutes of higher education that cover the entire curriculum. The university is a member of TU9, a consortium of the nine leading German Institutes of Technology. The university is one of eleven German universities which succeeded in the Excellence Initiative in 2012, thus getting the title of a “University of Excellence”. The TU Dresden succeeded in all three rounds of the German Universities Excellence Initiative (Future Concept, Graduate Schools, Clusters of Excellence).

History

In 1828, with emerging industrialization, the “Saxon Technical School” was founded to educate skilled workers in technological subjects such as mechanics; mechanical engineering and ship construction. In 1871 the year the German Empire was founded, the institute was renamed the Royal Saxon Polytechnic Institute (Königlich-Sächsisches Polytechnikum). At that time, subjects not connected with technology such as history and languages were introduced. By the end of the 19th century the institute had developed into a university covering all disciplines. In 1961 it was given its present name, Dresden University of Technology [Technische Universität Dresden].

Upon German reunification in 1990 the university had already integrated the College of Forestry (Forstliche Hochschule) formerly the Royal Saxony Academy of Forestry, in the nearby small town of Tharandt. This was followed by the integration of the Dresden College of Engineering (Ingenieurshochschule Dresden); the Friedrich List College of Transport (Hochschule für Verkehrswesen) the faculty of transport science; and the “Carl-Gustav Carus” Medical Academy (Medizinische Akademi), the medical faculty. Some faculties were newly founded: the faculties of Information Technology (1991); Law (1991); Education (1993); and Economics (1993).

In 2009 TU Dresden, all Dresden institutes of the Fraunhofer Society; the Gottfried Wilhelm Leibniz Scientific Community and the Max Planck Society and Forschungszentrum Dresden-Rossendorf soon incorporated into the Helmholtz Association of German Research Centres (DE), published a joint letter of intent with the name DRESDEN-Konzept – Dresden Research and Education Synergies for the Development of Excellence and Novelty, which points out worldwide elite aspirations, which was recognized as the first time that all four big post-gradual elite institutions declared campus co-operation with a university.

Sciences

With 4,390 students the Faculty of Mathematics and the Natural Sciences is the second-largest faculty at the university. It is composed of 5 departments: Biology; Chemistry; Mathematics; Physics; and Psychology. The departments are all located on the main campus. In 2006, a new research building for the biology department opened. In October 2006 the Deutsche Forschungsgemeinschaft decided to fund a new graduate school, the Dresden International Graduate School for Biomedicine and Bioengineering and a so-called cluster of excellence From Cells to Tissues to Therapies.

Engineering

The Faculty of Architecture comprises 6 departments. Currently, there are 1,410 students enrolled.
The Faculty of Civil Engineering is structured into 11 departments. It is the oldest and smallest of the faculties. There are currently 800 students enrolled.
The Faculty of Computer Science comprises six departments: Applied Computer Science; Artificial Intelligence; Software- and Multimedia-Technology; Systems Architecture; Computer Engineering; and Theoretical Computer Science. The faculty has 2,703 students.
The Faculty of Electrical Engineering and Information Technology is organized into 13 departments. There are 2,288 students enrolled. The faculty is the heart of the so-called Silicon Saxony in Dresden.
The Faculty of Environmental Sciences has 2,914 students. The faculty is located on the main campus, except for the Forestry department which is located in Tharandt. The Forestry department is the oldest of its kind in Germany. Its history goes back to the foundation of the Royal Saxon Academy of Forestry (Königlich-Sächsische Forstakademie) in 1816.
The Faculty of Mechanical Engineering comprises 19 departments and has 5,731 students. It is the largest faculty at TUD.
The Faculty of Transport and Traffic Sciences “Friedrich List” is the only of its kind in Germany covering transport and traffic from economy and system theory science to electrical, civil and mechanical engineering. There are 1,536 students enrolled.

Humanities and Social Sciences

The Faculty of Business and Economics comprises five departments: Business Education Studies (Wirtschaftspädagogik); Business Management; Economics; Business Information Systems; and Statistics. There are 2,842 students enrolled.
The Faculty of Education, located East of the main campus, has 2,075 students.
The Faculty of Languages, Literature and Culture is structured into five departments: American Studies; English Studies; German Studies; Philology; Romance Languages; and Slavic Studies. There are 3,215 students at this faculty.
The Faculty of Law is going to close in the next few years. Currently there are still 933 students enrolled. The TU Dresden has partially compensated the closure by establishing a private law school
The Faculty of Philosophy comprises seven departments: Art History; Communications; History; Musicology; Political Sciences; Sociology; and Theology. There are 3,485 students enrolled.
The School of International Studies is a so-called central institution of the university coordinating the law, economics and political sciences departments for courses of interdisciplinary international relations.

Medicine
The Carl Gustav Carus Faculty of Medicine has its own campus East of the city center near the Elbe river. Currently, there are 2,195 students enrolled. The faculty has a partnership with Partners Harvard Medical International.

Research Centers
Center for Advancing Electronics Dresden (cfaed) – Cluster of Excellence
Center for Regenerative Therapies Dresden (CRTD) – Cluster of Excellence
Dendro-Institute Tharandt at the TU Dresden
The European Institute for Postgraduate Education at TU Dresden (EIPOS Europäisches Institut für postgraduale Bildung an der Technischen Universität Dresden e. V.)
The European Institute of Transport (EVI Europäisches Verkehrsinstitut an der Technischen Universität Dresden e. V.)
The Hannah Arendt Center for Research on Totalitarianism (HAIT Hannah-Arendt-Institut für Totalitarismusforschung an der Technischen Universität Dresden e. V.)
Center for Media Culture (MKZ Medienkulturzentrum Dresden e. V. an der TU Dresden)
Center for Research on Mechanics of Structures and Materials (SWM Struktur- und Werkstoffmechanikforschung Dresden GmbH an der Technischen Universität Dresden)
TUD Vietnam ERC, the TU Dresden Vietnam Education and Research Center. The center offers a Master’s course in Mechatronics in Hanoi (Vietnam) since 2004.
Center for Continuing Education in Historic Preservation (WBD Weiterbildungszentrum für Denkmalpflege und Altbauinstandsetzung e. V.)
School of International Studies (Zentrum für Internationale Studien, ZIS in German)