Experimentally identifying effective theories in many-body systems
Heidelberg researchers develop new method and demonstrate its application
in experiments

Date:
June 22, 2020
Source:
University of Heidelberg
Summary:
One goal of science is to find physical descriptions of nature by
studying how basic system components interact with one another. For
complex many-body systems, effective theories are frequently used
to this end. They allow describing the interactions without having
to observe a system on the smallest of scales. Physicists have
developed a new method that makes it possible to identify such
theories experimentally with the aid of quantum simulators.



FULL STORY ==========================================================================
One goal of science is to find physical descriptions of nature by
studying how basic system components interact with one another. For
complex many-body systems, effective theories are frequently used to this
end. They allow describing the interactions without having to observe
a system on the smallest of scales. Physicists at Heidelberg University
have now developed a new method that makes it possible to identify such theories experimentally with the aid of so-called quantum simulators. The results of the research effort, led by Prof.

Dr Markus Oberthaler (experimental physics) and Prof. Dr Ju"rgen Berges (theoretical physics), were published in the journal Nature Physics.


========================================================================== Deriving predictions about physical phenomena at the level of individual particles from a microscopic description is practically impossible for
large systems. This applies not only to quantum mechanical many-body
systems, but also to classical physics, such as when heated water in
a cooking pot needs to be described at the level of the individual
water molecules. But if a system is observed on large scales, like
water waves in a pot, new properties can become relevant under certain preconditions. To describe such physics efficiently, effective theories
are used. "Our research aimed to identify these theories in experiments
with the help of quantum simulators," explains Torsten Zache, the primary author of the theoretical portion of the study. Quantum simulators are
used to modify many-body systems more simply and to calculate their
properties.

The Heidelberg physicists recently demonstrated their newly developed
method in an experiment on ultracold rubidium atoms, which are captured
in an optical trap and brought out of equilibrium. "In the scenario
we prepared, the atoms behave like tiny magnets whose orientation
we are able to precisely read out using new processes," according to
Maximilian Pru"fer, the primary author on the experimental side of the
study. To determine the effective interactions of these "magnets," the experiment has to be repeated several thousand times, which requires
extreme stability.

"The underlying theoretical concepts allow us to interpret the
experimental results in a completely new way and thereby gain insights
through experiments into areas that have thus far been inaccessible
through theory," points out Prof. Oberthaler. "In turn, this can
tell us about new types of theoretical approaches to successfully
describe the relevant physical laws in complex many- body systems,"
states Prof. Berges. The approach used by the Heidelberg physicists is transferrable to a number of other systems, thus opening groundbreaking territory for quantum simulations. Ju"rgen Berges and Markus Oberthaler
are confident that this new way of identifying effective theories will
make it possible to answer fundamental questions in physics.


========================================================================== Story Source: Materials provided by University_of_Heidelberg. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Maximilian Pru"fer, Torsten V. Zache, Philipp Kunkel, Stefan Lannig,
Alexis Bonnin, Helmut Strobel, Ju"rgen Berges, Markus K. Oberthaler.

Experimental extraction of the quantum effective action for a
non- equilibrium many-body system. Nature Physics, 2020; DOI:
10.1038/s41567- 020-0933-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200622133049.htm

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