Nav: Home

Testing quantum field theory in a quantum simulator

May 17, 2017

What happened right after the beginning of the universe? How can we understand the structure of quantum materials? How does the Higgs-Mechanism work? Such fundamental questions can only be answered using quantum field theories. These theories do not describe particles independently from each other; all particles are seen as a collective field, permeating the whole universe.

But these theories are often hard to test in an experiment. At the Vienna Center for Quantum Science and Technology (VCQ) at TU Wien, researchers have now demonstrated how quantum field theories can be put to the test in new kinds of experiments. They have created a quantum system consisting of thousands of ultra cold atoms. By keeping them in a magnetic trap on an atom chip, this atom cloud can be used as a "quantum simulator", which yields information about a variety of different physical systems and new insights into some of the most fundamental questions of physics.

Complex Quantum Systems -- More than the Sum of their Parts

"Ultra cold atoms open up a door to recreate and study fundamental quantum processes in the lab", says Professor Jörg Schmiedmayer (VCQ, TU Wien). A characteristic feature of such a system is that its parts cannot be studied independently.

The classical systems we know from daily experience are quite different: The trajectories of the balls on a billiard table can be studied separately -- the balls only interact when they collide.

"In a highly correlated quantum system such as ours, made of thousands of particles, the complexity is so high that a description in terms of its fundamental constituents is mathematically impossible", says Thomas Schweigler, the first author of the paper. "Instead, we describe the system in terms of collective processes in which many particles take part -- similar to waves in a liquid, which are also made up of countless molecules." These collective processes can now be studied in unprecedented detail using the new methods.

Higher Correlations

In high-precision measurements, it turns out that the probability of finding an individual atom is not the same at each point in space -- and there are intriguing relationships between the different probabilities. "When we have a classical gas and we measure two particles at two separate locations, this result does not influence the probability of finding a third particle at a third point in space", says Jörg Schmiedmayer. "But in quantum physics, there are subtle connections between measurements at different points in space. These correlations tell us about the fundamental laws of nature which determine the behaviour of the atom cloud on a quantum level."

"The so-called correlation functions, which are used to mathematically describe these relationships, are an extremely important tool in theoretical physics to characterize quantum systems", says Professor Jürgen Berges (Institute for Theoretical Physics, Heidelberg University). But even though they have played an important part in theoretical physics for a long time, these correlations could hardly be measured in experiments. With the help of the new methods developed at TU Wien, this is now changing: "We can study correlations of different orders - up to the tenth order. This means that we can investigate the relation between simultaneous measurements at ten different points in space", Schmiedmayer explains. "For describing the quantum system, it is very important whether these higher correlations can be represented by correlations of lower order -- in this case, they can be neglected at some point -- or whether they contain new information."

Quantum Simulators

Using such highly correlated systems like the atom cloud in the magnetic trap, various theories can now be tested in a well-controlled environment. This allows us to gain a deep understanding of the nature of quantum correlations. This is especially important because quantum correlations play a crucial role in many, seemingly unrelated physics questions: Examples are the peculiar behaviour of the young universe right after the big bang, but also for special new materials, such as the so-called topological insulators.

Important information on such physical systems can be gained by recreating similar conditions in a model system, like the atom clouds. This is the basic idea of quantum simulators: Much like computer simulations, which yield data from which we can learn something about the physical world, a quantum simulation can yield results about a different quantum system that cannot be directly accessed in the lab.
-end-
Further information:

Prof. Jörg Schmiedmayer
Institute of Atomic and Subatomic Physics
Vienna University of Technology
Stadionallee 2, 1020 Wien
T: +43-1-58801-141801
M: +43-664-605883888
hannes-joerg.schmiedmayer@tuwien.ac.at

Vienna University of Technology

Related Physics Articles:

Diamonds coupled using quantum physics
Researchers at TU Wien have succeeded in coupling the specific defects in two such diamonds with one another.
The physics of wealth inequality
A Duke engineering professor has proposed an explanation for why the income disparity in America between the rich and poor continues to grow.
Physics can predict wealth inequality
The 2016 election year highlighted the growing problem of wealth inequality and finding ways to help the people who are falling behind.
Physics: Toward a practical nuclear pendulum
Researchers from Ludwig-Maximilians-Universitaet (LMU) Munich have, for the first time, measured the lifetime of an excited state in the nucleus of an unstable element.
Flowers use physics to attract pollinators
A new review indicates that flowers may be able to manipulate the laws of physics, by playing with light, using mechanical tricks, and harnessing electrostatic forces to attract pollinators.
Physics, photosynthesis and solar cells
A University of California, Riverside assistant professor has combined photosynthesis and physics to make a key discovery that could help make solar cells more efficient.
2-D physics
Physicist Andrea Young receives a 2016 Packard Fellowship to pursue his studies of van der Waals heterostructures.
Cats seem to grasp the laws of physics
Cats understand the principle of cause and effect as well as some elements of physics.
Plasma physics' giant leap
For the first time, scientists are looking at real data -- not computer models, but direct observation -- about what is happening in the fascinating region where the Earth's magnetic field breaks and then joins with the interplanetary magnetic field.
Nuclear physics' interdisciplinary progress
The theoretical view of the structure of the atom nucleus is not carved in stone.

Related Physics Reading:

Basic Physics: A Self-Teaching Guide
by Karl F. Kuhn (Editor)

The Feynman Lectures on Physics, boxed set: The New Millennium Edition
by Richard P. Feynman (Author), Robert B. Leighton (Author), Matthew Sands (Author)

Fundamentals of Physics: Mechanics, Relativity, and Thermodynamics (The Open Yale Courses Series)
by R. Shankar (Author)

Seven Brief Lessons on Physics
by Carlo Rovelli (Author)

No bullshit guide to math and physics
by Ivan Savov (Author)

Modern Classical Physics: Optics, Fluids, Plasmas, Elasticity, Relativity, and Statistical Physics
by Kip S. Thorne (Author), Roger D. Blandford (Author)

Understanding Ultrasound Physics
by Sidney K Edelman (Author)

Baby University Four-Book Set
by Chris Ferrie (Author)

Introduction to Quantum Mechanics
by David J. Griffiths (Author), Darrell F. Schroeter (Author)

Mathematical Methods for Physics and Engineering: A Comprehensive Guide
by K. F. Riley (Author), M. P. Hobson (Author), S. J. Bence (Author)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Where Joy Hides
When we focus so much on achievement and success, it's easy to lose sight of joy. This hour, TED speakers search for joy in unexpected places, and explain why it's crucial to a fulfilling life. Speakers include inventor Simone Giertz, designer Ingrid Fetell Lee, journalist David Baron, and musician Meklit Hadero.
Now Playing: Science for the People

#499 Technology, Work and The Future (Rebroadcast)
This week, we're thinking about how rapidly advancing technology will change our future, our work, and our well-being. We speak to Richard and Daniel Susskind about their book "The Future of Professions: How Technology Will Transform the Work of Human Experts" about the impacts technology may have on professional work. And Nicholas Agar comes on to talk about his book "The Sceptical Optimist" and the ways new technologies will affect our perceptions and well-being.