Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Correlated magnets made out of single atoms

29.09.2016

Scientists at MPQ observe antiferromagnetic correlations in one-dimensional fermionic quantum many-body systems

Solid state physics offers a rich variety of intriguing phenomena, several of which are not yet fully understood. Experiments with fermionic atoms in optical lattices get very close to imitating the behaviour of electrons in solid state crystals, thus forming a well-controlled quantum simulator for these systems.


Graphics: Martin Boll, Quantum Many-Body Systems Division, MPQ

Now a team of scientists around Professor Immanuel Bloch and Dr. Christian Groß at the Max Planck Institute of Quantum Optics have observed the emergence of antiferromagnetic order over a correlation length of several lattice sites in a chain of fermionic atoms. Contrary to the ferromagnetism we experience in everyday life, these antiferromagnets are characterized by an alternating alignment of the elementary magnetic moment associated with each electron or atom.

Combining their quantum gas microscope with advanced local manipulation techniques, the scientists were able to simultaneously observe the spin and the density distribution with single-site resolution and single atom sensitivity. By approaching the conditions prevailing in macroscopic crystals with fermionic quantum many-body systems, one hopes to achieve a better understanding of phenomena such as the so-called high-temperature superconductivity. (Science, 16 September 2016, DOI:10.1126/science.aag1635).

The experiment started with cooling a cloud of fermionic lithium-6 atoms down to extremely low temperatures, a millionth of a Kelvin above absolute zero. These ultracold fermions were then trapped by light fields and forced into a single plane, which in turn was further split in several one-dimensional tubes. Finally, an optical lattice was applied along the tubes mimicking the periodic potential that electrons see in a real material.

On average, the one-dimensional optical lattices were completely filled, meaning that each lattice site was occupied with exactly one atom. Two internal quantum states of the lithium atoms mimic the magnetic moment of the electrons, which can point either upwards or downwards. As long as the temperature of the system is high compared to the magnetic interaction between these spins, only the density distribution of the system shows a regular pattern dictated by the optical lattice. However, below a certain temperature the magnetic moments of neighbouring atoms are expected to anti-align, leading to antiferromagenic correlations. “These correlations arise because the system aims to lower its energy”, Martin Boll, doctoral student at the experiment, explains. “The underlying mechanism is called “superexchange” which means that the magnetic moments of neighbouring atoms exchange their directions.”

The team around Christian Groß and Immanuel Bloch had to tackle two main challenges: First, it was necessary to measure the particle density with high resolution to unambiguously identify single particles and holes on their individual lattice sites. This was achieved with the quantum gas microscope where a high resolution objective images the atoms all at once, such that a series of photographic snapshots of the atomic gas can be taken. “The second really big challenge was the separation of atoms based on their magnetic orientations”, says Martin Boll. “To this end, we combined an optical superlattice with a magnetic gradient that shifted the potential minima depending on the orientation of the magnetic moment. As a consequence, opposite magnetic moments were separated into two different sites of the local double well potential created by the superlattice. In a series of measurements we have tuned this method to such a degree that we obtained a splitting fidelity of nearly 100 percent.”

Having all these tools at hand, the team succeeded to observe the emergence of antiferromagnetic correlations that extended over three sites, well beyond nearest-neighbours (see figure 1). “Quantum simulations with fermions in optical lattices is of particular interest because it may lead to a better understanding of the so-called “high-temperature” superconductivity for which the interplay of holes and antiferromagnetic correlations is believed to be crucial.”, Dr. Christian Groß points out. “In the near future, we might be able to even prepare our samples with a certain degree of hole-doping that resembles the conditions in superconducting materials.” Olivia Meyer-Streng

Original publication:
Martin Boll, Timon A. Hilker, Guillaume Salomon, Ahmed Omran, Jacopo Nespolo, Lode Pollet, Immanuel Bloch, Christian Gross
Spin- and density-resolved microscopy of antiferromagnetic correlations in Fermi-Hubbard chains
Science, 16 September 2016, DOI:10.1126/science.aag1635

Contact:
Prof. Dr. Immanuel Bloch
Chair of Quantum Optics
Ludwig-Maximilians-Universität Munich, and
Director at the Max Planck Institute of
Quantum Optics
Hans-Kopfermann-Straße 1, 85748 Garching,
Phone: +49 (0)89 / 32 905 - 138
E-mail: immanuel.bloch@mpq.mpg.de

Dr. Christian Groß
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 713
E-mail: christian.gross@mpq.mpg.de

Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 213
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut für Quantenoptik
Further information:
http://www.mpq.mpg.de/

More articles from Physics and Astronomy:

nachricht Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology

nachricht A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Study shines light on brain cells that coordinate movement

26.06.2017 | Life Sciences

Smooth propagation of spin waves using gold

26.06.2017 | Physics and Astronomy

Switchable DNA mini-machines store information

26.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>