Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


A dynamical quantum simulator

An international collaboration demonstrates the superiority of a dynamical quantum simulator over state-of-the-art numerical calculations.

The key prospect of a quantum simulator is to access new physics that the best known classical algorithms can no longer keep track of.

Figure: (left) Schematics of the experiments probing the non-equilibrium dynamics emerging when an initially prepared density wave of ultracold atoms in an optical lattice is subjected to a tunnel coupling and inter-particle interactions. (right) The experimental data is well reproduced by parameter-free numerical simulations (black line) which however break down for longer evolution times. Here, the experiment (blue circles) can still deliver reliable results, serving as a quantum simulator of many-body dynamics. Grafik: MPQ

For the first time, a group around Professor Immanuel Bloch (Max Planck Institute of Quantum Optics and Ludwig-Maximilians-Universität Munich), in collaboration with theoretical physicists from the Ludwig-Maximilians-Universität Munich of the group of Prof. Ulrich Schollwöck, the Forschungszentrum Jülich, the Institute for Advanced Study Berlin, and the University of Queensland (Australia), has demonstrated this superiority by following the dynamics of a quantum system of strongly correlated ultracold atoms in an optical lattice.

In particular they were able to follow the relaxation of the isolated system which was initialized in a state far from equilibrium. The experimentally observed dynamics were in excellent agreement with numerical calculations which are available only for short evolution times (Nature Physics, AOP, 19 February 2012, Doi:10.1038/nphys2232). This demonstrates that many-body systems of ultracold atoms can be used as quantum simulators in a regime which is not accessible for classical computers.

The concept of thermalization and thermal equilibrium is fundamental to a large part of our everyday life. It explains, for example, how hot coffee in a cup cools down to room temperature while also heating the room a little, and how the motion of the molecules in the coffee that is induced by stirring it with a spoon will dampen out until everything is at rest again. The answer to the same fundamental question posed in the context of a closed quantum system of interacting particles brought out of equilibrium remains elusive to the present day. The complexity of the underlying quantum dynamics as well as the possibility of the quantum particles to become entangled with one another makes even sophisticated numerical methods fail in the attempt to address this problem for large particle numbers and long timescales. Experiments with ultracold rubidium atoms carried out in the group of Professor Immanuel Bloch now allow the scientists to follow the non-equilibrium evolution of an interacting quantum many-body system on a time-scale much longer than those accessible by exact numerical methods.

In the experiments, an extremely cold gas of rubidium atoms was loaded into an optical lattice: a periodic structure of bright and dark areas, created by the interference of counter-propagating laser beams. In this structure, the atoms are held in either dark or bright spots, depending on the wavelength of the light, and therefore align themselves in a regular pattern. The use of an additional light field with twice the spatial period allowed the scientists to pairwise group adjacent lattice sites in an optical superlattice and to further manipulate the regular pattern to obtain a configuration with alternatingly filled and empty sites along one spatial direction. Starting from this ’density wave’ state far from equilibrium, the atoms are then allowed to tunnel along the same spatial direction and to collide with one and another, leading to a complex many-body dynamics. After a certain relaxation-time, the system’s properties were read out in terms of local densities, tunnel currents and nearest-neighbour correlations with the help of the superlattice. These observables were probed for a variety of lattice heights and evolution times, showing a rapid relaxation to (quasi-) steady state values.

On short timescales, parameter-free numerical simulations carried out by collaborators of several research institutes could track the many-body dynamics and therefore benchmark the experimental quantum simulation. For long evolution times, however, these classical methods have to fail for the concomitant entanglement growth rendering a classical description infeasible. The experiment, on the other hand, tracks the evolution well beyond the time scale of theoretical predictions. This demonstrates that this system of ultracold atoms can be used as an efficient simulator for relaxation physics in many-body systems and is outperforming the best classical simulation so far. Furthermore, the experiment gives insight into quantum mechanical tunnel processes as well as (quasi-) steady state properties after relaxation. It opens up new avenues in the study of cold atoms in non-equilibrium which leads to a better understanding of fundamental problems in condensed matter physics. [ST/OM]

Original Publication:
S. Trotzky, Y-A. Chen, A. Flesch, I. P. McCulloch, U. Schollwöck, J. Eisert & I. Bloch
Probing the relaxation towards equilibrium in an isolated strongly correlated one-dimensional Bose gas

Nature Physics, AOP, 19 February 2012, Doi:10.1038/nphys2232


Prof. Dr. Immanuel Bloch
Chair of Quantum Optics
LMU Munich, Schellingstr. 4
80799 München, Germany, and
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching b. München
Phone: +49 89 / 32905 -138
Prof. Dr. Ulrich Schollwöck
Chair of Theoretical Nanophysics, LMU München
Theresienstr. 37
80333 München
Phone: +49 89 / 2180 -4117
Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 89 / 32905 -213
E-mail: olivia.meyer-streng@mpq.mpg

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

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: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>