The formation of quasiparticles, such as polarons, in a condensed-matter system usually proceeds in an extremely fast way and is very difficult to observe. In Innsbruck, Rudolf Grimm’s physics research group, in collaboration with an international team of theoretical physicists, has simulated the formation of polarons in an ultracold quantum gas in real time. The researchers have published their findings in the journal Science.
The concept of quasiparticles is a powerful tool to describe processes in many-body quantum systems, such as solid-state materials. For example, when an electron moves through a solid, it generates polarization in its environment because of its electrical charge.
This “polarization cloud” moves together with the electron and the resulting “dressed electron” can be theoretically described as quasiparticle or a polaron. “You could picture it as a skier on a powder day,” says Grimm. “The skier is surrounded by a cloud of snow crystals. Together they form a system that has different properties than the skier without the cloud.”
The challenge in an experiment is to measure the quasiparticles. “These processes last only attoseconds, which makes a time-resolved observation of their formation extremely difficult,” explains Grimm. His research group uses ultracold quantum gases for simulations to study the many-body physics of complex quantum systems.
Observing the birth of quasiparticles
Ultracold quantum gases are an ideal experimental platform to study physical phenomena in solid-state materials and also exotic states of matter, for example neutron stars. Because of the well-controlled environment, the scientists are able to create many-body states and manipulate interactions between particles in these gases. Rudolf Grimm’s research group, working at the Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, and the Institute for Experimental Physics, University of Innsbruck, is a leader in this research field.
In collaboration with theoretical physicists from Harvard University, the TU Munich and Monash University in Australia, the researchers have now studied quasiparticle dynamics in real time. In a vacuum chamber, using laser trapping techniques, the researchers created an ultracold quantum gas made up of lithium atoms and a small sample of potassium atoms in the center. For both types of atoms they used isotopes of fermionic nature, which belong to the same fundamental class as electrons.
Magnetic fields were used to tune interactions, which produced Fermi polarons, i.e. potassium atoms embedded in a lithium cloud. “In condensed matter, the natural time scale of these quasiparticles is on the order of 100 attoseconds,” explains Grimm. “We simulated the same physical processes at much lower densities. Here, the formation time for polarons is a few microseconds.”
However, measurement still remains a challenge. “We developed a new method for observing the ‘birth’ of a polaron virtually in real time,” says quantum physicists Grimm. Looking into the future, he says: “This may turn out to be a very interesting approach to better understand the quantum physical properties of ultrafast electronic devices.”
The scientists are supported, among others, by the Austrian Science Fund (FWF) within the framework of the Special Research Area program (SFB) FoQuS and the Doctoral Program Atoms, Light and Molecules (ALM).
Publication: Ultrafast many-body interferometry of impurities coupled to a Fermi sea. Marko Cetina, Michael Jag, Rianne S. Lous, Isabella Fritsche, Jook T. M. Walraven, Rudolf Grimm, Jesper Levinsen, Meera M. Parish, Richard Schmidt, Michael Knap, Eugene Demler. Science 2016 DOI: 10.1126/science.aaf5134
Institute for Experimental Physics
University of Innsbruck
Phone: +43 512 507-52410
Public Relations Office
University of Innsbruck
Phone: +43 512 507 32022
Mobile: +43 676 872532022
http://dx.doi.org/10.1126/science.aaf5134 - Ultrafast many-body interferometry of impurities coupled to a Fermi sea. Marko Cetina, Michael Jag, Rianne S. Lous, Isabella Fritsche, Jook T. M. Walraven, Rudolf Grimm, Jesper Levinsen, Meera M. Parish, Richard Schmidt, Michael Knap, Eugene Demler. Science 2016
http://www.ultracold.at - Research Group Ultracold Atoms and Quantum Gases
http://iqoqi.at - Institute of Quantum Optics and Quantum Information (IQOQI)
Dr. Christian Flatz | Universität Innsbruck
Meteoritic stardust unlocks timing of supernova dust formation
19.01.2018 | Carnegie Institution for Science
Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy