The design of new materials with specific properties is a difficult and important challenge in physics and chemistry. Nobel Prize winner Richard P. Feynman in 1982 therefore suggested to build a "quantum simulator" in order to understand and predict the properties of complex materials by simulating them using an artificial, but highly controllable different quantum system. In the latest issue of the journal Science a team of scientists led by Prof. Immanuel Bloch, director at MPQ and chair of physics at the Johannes Gutenberg Universität of Mainz show how to simulate the properties of electrons in a real crystal by using ultracold atoms trapped in an artificial crystal formed by interfering laser beams - a so called optical lattice. The researchers from the University of Mainz, the University of Cologne and the Forschungszentrum Jülich succeeded in demonstrating one of the most dramatic effects of the electron-electron repulsion: When the interactions between the electrons get too strong, a metal can suddenly become insulating. The resulting so-called Mott-insulator is probably the most important example of a strongly correlated state in condensed matter physics, and it is a natural starting point for the investigation of quantum magnetism. In addition, high temperature superconductivity is found to arise in close proximity to it.
An artists impression of the fermionic Mott insulating state: Due to the dominating repulsive interaction every lattice site is occupied by exactly one atom. The different colors indicate different spin states. Universität Mainz
"Atoms in an optical lattice are a nearly perfect quantum simulator for electrons in a solid, as they offer a very flexible model-system in a clean and well-controlled environment" explains Ulrich Schneider from the University of Mainz. Investigating complex materials and high temperature superconductors is difficult because of the presence of disorder and many competing interactions in the real crystalline materials. "This makes it difficult to identify the role of specific interactions and, in particular, to decide whether repulsive interactions between fermions alone can explain high temperature superconductivity" says Prof. Bloch.
In the experiment, a gas of potassium atoms is first cooled down to almost zero temperature. Subsequently, an optical lattice is created by overlapping several laser beams. To the atoms, the resulting standing-wave laser field appears as a regular crystal of tens of thousands of individual micro-traps, similar to an array of optical tweezers. The ultracold atoms, which assume the role of electrons in real solids, will line up at the nodes of this standing-wave field.
By investigating the behaviour of the atoms under compression and increasing interaction strength, and thereby measuring their compressibility, the experimentalists have been able to controllably switch the system between metallic and insulating states of matter and find evidence for a Mott-insulating phase within the quantum gas of fermionic atoms. In such a Mott insulating phase, the repulsive interactions between the atoms force them to order one-by-one into the regular lattice structure.
The observation of the fermionic Mott-insulator in the context of optical lattices opens up a new possibility to simulate and study strongly correlated states and related phenomena. This is affirmed by the excellent agreement achieved in comparing the experiment with theoretical calculations of modern condensed matter theory performed in Cologne and Jülich, which included extensive simulations on the Jülich based supercomputer system JUGENE. [I.B.]
Science, 5th December 2008More information and picture gallery:
New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center
Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research