IT'S A QUANTUM UNIVERSE

Progress in quantum physics: Researchers tame superconductors

UNIVERSITY OF WÜRZBURG

Superconductors are materials that can conduct electricity without electrical resistance – making them the ideal base material for electronic components in MRI machines, magnetic levitation trains and even particle accelerators. However, conventional superconductors are easily disturbed by magnetism. An international group of researchers has now succeeded in building a hybrid device consisting of a stable proximitized-superconductor enhanced by magnetism and whose function can be specifically controlled.

They combined the superconductor with a special semiconductor material known as a topological insulator. “Topological insulators are materials that conduct electricity on their surface but not inside. This is due to their unique topological structure, i.e. the special arrangement of the electrons,“ explains Professor Charles Gould, a physicist at the Institute for Topological Insulators at the University of Würzburg (JMU). “The exciting thing is that we can equip topological insulators with magnetic atoms so that they can be controlled by a magnet.“

The superconductors and topological insulators were coupled to form a so-called Josephson junction, a connection between two superconductors separated by a thin layer of non-superconducting material. “This allowed us to combine the properties of superconductivity and semiconductors“, says Gould. “So we combine the advantages of a superconductor with the controllability of the topological insulator. Using an external magnetic field, we can now precisely control the superconducting properties. This is a true breakthrough in quantum physics!“

Superconductivity Meets Magnetism

The special combination creates an exotic state in which superconductivity and magnetism are combined – normally these are opposite phenomena that rarely coexist. This is known as the proximity-induced Fulde-Ferrell-Larkin-Ovchinnikov (p-FFLO) state. The new “superconductor with a control function“ could be important for practical applications, such as the development of quantum computers. Unlike conventional computers, quantum computers are based not on bits but on quantum bits (qubits), which can assume not just two but several states simultaneously.

“The problem is that quantum bits are currently very unstable because they are extremely sensitive to external influences, such as electric or magnetic fields“, says physicist Gould. “Our discovery could help stabilise quantum bits so that they can be used in quantum computers in the future.“

International Quantum Research Team

The experimental research was carried out by a team from the Chair of Experimental Physics III of Professor Laurens W. Molenkamp in Würzburg. It was carried out in close collaboration with theoretical experts from the group of Professor F. Sebastian Bergeret of the Centre for Materials Physics (CFM) in San Sebastian, Spain, and Professor Teun M. Klapwijk of Delft University of Technology in the Netherlands.

The international research group was funded by the Cluster of Excellence ct.qmat (Complexity and Topology in Quantum Materials), the German Research Foundation (DFG), the Free State of Bavaria, the Spanish Agencia Estatal de Investigación (AEI), the European research programme Horizon 2020 and the EU ERG Advanced Grant Programme.

Cluster of Excellence ct.qmat

The Würzburg team participates in the Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter, which has been jointly run by the University of Würzburg (JMU) and Technische Universität (TU) Dresden since 2019. Over 300 scientists from more than thirty countries and four continents study topological quantum materials that reveal surprising phenomena under extreme conditions such as ultra-low temperatures, high pressure, or strong magnetic fields. ct.qmat is funded through the German Excellence Strategy of the Federal and State Governments and is the only Cluster of Excellence in Germany to be based in two different federal states.

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JOURNAL

Nature Physics

DOI

10.1038/s41567-024-02477-1 

METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

Magnetically tunable supercurrent in dilute magnetic topological insulator-based Josephson junctions

ARTICLE PUBLICATION DATE

1-Apr-2024

Chemical reactions can scramble quantum information as well as black holes

Peer-Reviewed Publication

RICE UNIVERSITY

 

IMAGE: 

CHENGHAO ZHANG (LEFT) AND SOHANG KUNDU

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CREDIT: (PHOTO OF ZHANG BY BILL WIEGAND/UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN; PHOTO OF KUNDU COURTESY OF SOHANG KUNDU)

HOUSTON – (April 5, 2024) – If you were to throw a message in a bottle into a black hole, all of the information in it, down to the quantum level, would become completely scrambled. Because in black holes this scrambling happens as quickly and thoroughly as quantum mechanics allows, they are generally considered nature’s ultimate information scramblers.

New research from Rice University theorist Peter Wolynes and collaborators at the University of Illinois Urbana-Champaign, however, has shown that molecules can be as formidable at scrambling quantum information as black holes. Combining mathematical tools from black hole physics and chemical physics, they have shown that quantum information scrambling takes place in chemical reactions and can nearly reach the same quantum mechanical limit as it does in black holes. The work is published online in the Proceedings of the National Academy of Sciences.

“This study addresses a long-standing problem in chemical physics, which has to do with the question of how fast quantum information gets scrambled in molecules,” Wolynes said. “When people think about a reaction where two molecules come together, they think the atoms only perform a single motion where a bond is made or a bond is broken.

“But from the quantum mechanical point of view, even a very small molecule is a very complicated system. Much like the orbits in the solar system, a molecule has a huge number of possible styles of motion ⎯ things we call quantum states. When a chemical reaction takes place, quantum information about the quantum states of the reactants becomes scrambled, and we want to know how information scrambling affects the reaction rate.”

To better understand how quantum information is scrambled in chemical reactions, the scientists borrowed a mathematical tool typically used in black hole physics known as out-of-time-order correlators, or OTOCs.

“OTOCs were actually invented in a very different context about 55 years ago, when they were used to look at how electrons in superconductors are affected by disturbances from an impurity,” Wolynes said. “They’re a very specialized object that is used in the theory of superconductivity. They were next used by physicists in the 1990s studying black holes and string theory.”

OTOCs measure how much tweaking one part of a quantum system at some instant in time will affect the motions of the other parts ⎯ providing insight into how quickly and effectively information can spread throughout the molecule. They are the quantum analog of Lyapunov exponents, which measure unpredictability in classical chaotic systems.

“How quickly an OTOC increases with time tells you how quickly information is being scrambled in the quantum system, meaning how many more random looking states are getting accessed,” said Martin Gruebele, a chemist at Illinois Urbana-Champaign and co-author on the study who is a part of the joint Rice-Illinois Center for Adapting Flaws as Features funded by the National Science Foundation. “Chemists are very conflicted about scrambling in chemical reactions, because scrambling is necessary to get to the reaction goal, but it also messes up your control over the reaction.

“Understanding under what circumstances molecules scramble information and under what circumstances they don’t potentially gives us a handle on actually being able to control the reactions better. Knowing OTOCs basically allows us to set limits on when this information is really disappearing out of our control and conversely when we could still harness it to have controlled outcomes.”

In classical mechanics, a particle must have enough energy to overcome an energy barrier for a reaction to occur. However, in quantum mechanics, there’s the possibility that particles can “tunnel” through this barrier even if they don’t possess sufficient energy. The calculation of OTOCs showed that chemical reactions with a low activation energy at low temperatures where tunneling dominates can scramble information at nearly the quantum limit, like a black hole.

Nancy Makri, also a chemist at Illinois Urbana-Champaign, used path integral methods she has developed to study what happens when the simple chemical reaction model is embedded in a larger system, which could be a large molecule’s own vibrations or a solvent, and tends to suppress chaotic motion.

“In a separate study, we found that large environments tend to make things more regular and suppress the effects that we’re talking about,” Makri said. “So we calculated the OTOC for a tunneling system interacting with a large environment, and what we saw was that the scrambling was quenched ⎯ a big change in the behavior.”

One area of practical application for the research findings is to place limits on how tunneling systems can be used to build qubits for quantum computers. One needs to minimize information scrambling between interacting tunneling systems to improve the reliability of quantum computers. The research could also be relevant for light-driven reactions and advanced materials design.

“There’s potential for extending these ideas to processes where you wouldn’t just be tunneling in one particular reaction, but where you’d have multiple tunneling steps, because that’s what’s involved in, for example, electron conduction in a lot of the new soft quantum materials like perovskites that are being used to make solar cells and things like that,” Gruebele said.

Wolynes is Rice’s D.R. Bullard-Welch Foundation Professor of Science, a professor of chemistry, f biochemistry and cell biology, physics and astronomy and materials science and nanoengineering and co-director of its Center for Theoretical Biological Physics, which is funded by the National Science Foundation. Co-authors Gruebele is the James R. Eiszner Endowed Chair in Chemistry; Makri is the Edward William and Jane Marr Gutgsell Professor and professor of chemistry and physics; Chenghao Zhang was a graduate student in physics at Illinois Urbana-Champaign and is now a postdoc at Pacific Northwest National Lab; and Sohang Kundu recently received his Ph.D. in chemistry from the University of Illinois and is currently a postdoc at Columbia University.

The research was supported by the National Science Foundation (1548562, 2019745, 1955302) and the Bullard-Welch Chair at Rice (C-0016).

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This press release can be found online at news.rice.edu.

Follow Rice News and Media Relations via Twitter @RiceUNews.

Peer-reviewed paper:

“Quantum information scrambling and chemical reactions” | Proceedings of the National Academy of Sciences | DOI: 10.1073/pnas.2321668121

Authors: Chenghao Zhang, Sohang Kundu, Nancy Makri, Martin Gruebele and Peter Wolynes

https://doi.org/10.1073/pnas.2321668121

Image downloads:

https://news-network.rice.edu/news/files/2024/04/BlackHoleMolecule2-0387e2be407aefaa.jpg
CAPTION: Rice University theorist Peter Wolynes and collaborators at the University of Illinois Urbana-Champaign have shown that molecules can be as formidable at scrambling quantum information as black holes. (Image courtesy of Martin Gruebele; DeepAI was used in the making of the image)

https://news-network.rice.edu/news/files/2024/04/Wolynes_Makri_Gruebele-3e4286b5ec5ad9fc.jpg
CAPTION: Peter Wolynes (from left), Nancy Makri and Martin Gruebele (Photo of Wolynes Gustavo Raskosky/Rice University; photo of Makri courtesy of Nancy Makri; photo of Gruebele by Fred Zwicky/University of Illinois Urbana-Champaign)

https://news-network.rice.edu/news/files/2024/04/Zhang_Kundu-66fa4d09a6f863a9.jpg
CAPTION: Chenghao Zhang (left) and Sohang Kundu (Photo of Zhang by Bill Wiegand/University of Illinois Urbana-Champaign; photo of Kundu courtesy of Sohang Kundu)

Related stories:

Theory can sort order from chaos in complex quantum systems:
https://news.rice.edu/news/2023/theory-can-sort-order-chaos-complex-quantum-systems

Rice lab’s quantum simulator delivers new insight:
https://news.rice.edu/news/2022/rice-labs-quantum-simulator-delivers-new-insight

NSF renews Rice biological physics center:
https://news.rice.edu/news/2020/nsf-renews-rice-biological-physics-center

Links:

Center for Adapting Flaws as Features: https://nsfcaff.org/
Gruebele Lab: https://gruebele-group.chemistry.illinois.edu/
BioScience Research Collaborative: https://brc.rice.edu/
Center for Theoretical Biological Physics: https://ctbp.rice.edu/
Department of Chemical and Biomolecular Engineering: https://chbe.rice.edu/
Department of Chemistry: https://chemistry.rice.edu/
Department of Physics and Astronomy: https://physics.rice.edu/
George R. Brown School of Engineering: https://engineering.rice.edu
Ken Kennedy Institute: https://kenkennedy.rice.edu/
Wiess School of Natural Sciences: https://naturalsciences.rice.edu
Wolynes Research Lab: https://wolynes.rice.edu/
Makri Group: http://makri.scs.illinois.edu/
Department of Chemistry, University of Illinois: https://chemistry.illinois.edu/

About Rice:

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of architecture, business, continuing studies, engineering, humanities, music, natural sciences and social sciences and is home to the Baker Institute for Public Policy. With 4,574 undergraduates and 3,982 graduate students, Rice’s undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction, No. 2 for best-run colleges and No. 12 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger’s Personal Finance.

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JOURNAL

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2321668121 

ARTICLE TITLE

Quantum information scrambling and chemical reactions

ARTICLE PUBLICATION DATE

1-Apr-2024

NEWS RELEASE 5-APR-2024

With VECSELs towards the quantum internet

Fraunhofer IAF achieves record output power with VECSEL for quantum frequency converters

FRAUNHOFER INSTITUTE FOR APPLIED SOLID STATE PHYSICS

 

IMAGE: 

VECSEL SETUP FOR THE DEVELOPMENT OF A LOW-NOISE PUMP SOURCE FOR QUANTUM FREQUENCY CONVERSION

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CREDIT: © FRAUNHOFER IAF

The expansion of fiber optics is progressing worldwide, which not only increases the bandwidth of conventional Internet connections, but also brings closer the realization of a global quantum Internet. The quantum internet can help to fully exploit the potential of certain technologies. These include much more powerful quantum computing through the linking of quantum processors and registers, more secure communication through quantum key distribution or more precise time measurements through the synchronization of atomic clocks.

However, the differences between the glass fiber standard of 1550 nm and the system wavelengths of the various quantum bits (qubits) realized to date represent a hurdle, because those qubits are mostly in the visible or near-infrared spectral range. Researchers want to overcome this obstacle with the help of quantum frequency conversion, which can specifically change the frequencies of photons while retaining all other quantum properties. This enables conversion to the 1550 nm telecom range for low-loss, long-range transmission of quantum states.

Project HiFi: Enabling technologies for quantum frequency conversion

In the joint project “HiFi — Highly integrated quantum frequency converter of highest fidelity based on innovative laser, fiber and production technology” funded by the German Federal Ministry of Education and Research (BMBF), researchers are working on the realization of all necessary technologies to provide quantum frequency converters (QFK) with high efficiency and low noise for initial test tracks. The Fraunhofer Institute for Applied Solid State Physics IAF has contributed to the project with the successful development of disk lasers (also known as vertical-external-cavity surface-emitting lasers, VECSELs) based on gallium antimonide (GaSb). These are optically pumped, surface-emitting semiconductor lasers with an external resonator and intracavity filter for wavelength selection.

2.4 W output power with absolute frequency stability below 100 kHz

“The VECSELs we developed as part of HiFi are spectrally narrow-band pump sources which, depending on the output wavelength of the qubits used, specifically cover a wavelength between 1.9 and 2.5 µm and achieve an output power of up to 2.4 W with an absolute wavelength stability of less than 2 fm. This corresponds to a frequency stability of less than 100 kHz and clearly falls below the frequency stability class 1E-9. The result represents an international record for this type of laser,” explains Dr. Marcel Rattunde, HiFi sub-project coordinator and head of the optoelectronics department at Fraunhofer IAF.

“The result was made possible by the close cooperation with project partner MENLO Systems GmbH. Together, we locked the disk laser to a frequency comb, which in turn was coupled to a 10 MHz reference,” emphasizes Rattunde.

In their experiments, the researchers set the emission wavelength exactly to the target wavelength for demonstration experiments at the fiber link of Saarland University (2062.40 nm), to which Fraunhofer IAF has handed over the laser module. In addition to power scaling, the most important research tasks of Fraunhofer IAF in the HiFi project are the precise understanding of the mode behavior of the lasers and the identification and elimination of noise sources.

Quantum frequency conversion using pump lasers

In quantum frequency conversion, the energy of the pump photon is subtracted from the signal photon by a difference frequency process in a non-linear optical crystal. To ensure a low-noise process, the energy of the pump photons must be below the target wavelength (usually 1550 nm), otherwise the pump laser can generate photons in the output signal due to parasitic effects.

In combination with the MENLO frequency comb, the VECSELs developed at Fraunhofer IAF meet the high requirements of quantum frequency conversion, as their narrow bandwidth and wavelength stability prevent fluctuations in the pump wavelength and consequently changes in the target wavelength of the qubits. If there is a deviation above the natural linewidth, the qubits would no longer be indistinguishable, which would eliminate a basic requirement for subsequent quantum mechanical processing.

VECSEL module für quantum frequency conversion 

Single-mode VECSEL module with up to 2.4 W output power for the frequency range between 1.9 and 2.5 µm, developed as a pump source for quantum frequency converters

CREDIT

© Fraunhofer IAF

Fraunhofer IAF at Photonics Europe 2024

From April 7 to 11, 2024, Fraunhofer IAF researchers will present their latest research results in the field of optoelectronics at this year’s SPIE Photonics Europe in Strasbourg.

Steffen Adler will talk about the HiFi project results on April 11 at 2 pm in his presentation “High-power 2 μm GaSb-based VECSEL with an absolute wavelength stability below 1 MHz”.

All presentations at a glance:

• Marko Härtelt: “Multiplexed dual-core QCL-based sensor for real-time standoff-spectroscopy in crime scene investigations” (April 8, 4:30 p.m., Schuman, Level 1)
• Thorsten Passow: “Optimization of AlGaAs-based Bragg-reflection waveguides for entangled photon sources” (9 April, 18:10, Galerie Schweitzer, Level 0)
• Peter Holl: “Light Source based on Adiabatic Frequency Conversion in Whispering Gallery Resonators tailored for holographic metrology” (April 10, 10:00 a.m., Rome, Level 0)
• Steffen Adler: “High-power 2 μm GaSb-based VECSEL with an absolute wavelength stability below 1 MHz” (April 11, 14:00, Dresde/Salon 13, Level 1)

Further information

Program of SPIE Photonics Europe 2024: https://spie.org/conferences-and-exhibitions/photonics-europe/programme/browse-programme#_=_

Optoelectronics at Fraunhofer IAF: https://www.iaf.fraunhofer.de/en/researchers/optoelectronic-devices.html

HiFi project profile: https://www.iaf.fraunhofer.de/en/researchers/optoelectronic-devices/Hifi.html

About Fraunhofer IAF

The Fraunhofer Institute for Applied Solid State Physics IAF is one of the world's leading research institutions in the fields of III-V semiconductors and synthetic diamond. Based on these materials, Fraunhofer IAF develops components for future-oriented technologies, such as electronic circuits for innovative communication and mobility solutions, laser systems for real-time spectroscopy, novel hardware components for quantum computing as well as quantum sensors for industrial applications. With its research and development, the Freiburg research institute covers the entire value chain — from materials research, design and processing to modules, systems and demonstrators. www.iaf.fraunhofer.de/en