Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Highway for ultracold atoms in light crystals

09.07.2014

LMU/MPQ-physicists succeed in realizing an analogue of the Meissner effect by measuring edge currents in a ladder-like crystal of light.

When a superconductor is exposed to a magnetic field, a current on its surface appears which creates a counter field that cancels the magnetic field inside the superconductor.


Schematic representation of the light crystal with ladder-like shape. The blue and yellow spheres represent the atoms traveling in opposite directions, as in the Meissner phase. In the experiment the strength of the current was measured, which indicated a transition from the vortex to the Meissner phase. (Graphic: MPQ, Quantum Many Body Systems Division)

This phenomenon, known as “Meissner-Ochsenfeld effect” after its discoverers, was first observed in 1933. This quantum effect has found applications in a large variety of fields, ranging from magnetic levitation of objects to medicine and industry.

For the first time, scientists in the group of Professor Immanuel Bloch (Ludwig-Maximilians-University, Munich and Max Planck Institute of Quantum Optics, Garching) in collaboration with theoretical physicist Dr. Belén Paredes from the Institute for Theoretical Physics (IFT) in Madrid have succeeded in measuring an analogue of the Meissner effect in an optical crystal with ultracold atoms.

The system realized by the team in fact constitutes the minimal system in which such a Meissner analogue can be observed and realizes theoretical predictions dating back more than 20 years. Furthermore, the scientists have been able to observe a transition from this Meissner phase to a vortex phase where the ‘screening’ of the external field breaks down. (Nature Physics, 2998 (2014)).

When a superconductor is cooled down below its critical temperature, which is typically on the order of a few tens of Kelvin, it undergoes a phase transition to a superconducting state. In that state, in addition to be able to transport electric currents without losses, the material presents a very special feature: when it is exposed to an external magnetic field, a current appears on its surface that fully cancels the field in its core.

As the external field is increased, the strength of the current also increases. This feature, called Meissner effect, is of key importance in condensed matter physics. For some special types of superconductors this effect can only exist up to a critical strength of the external field. If the field is increased above that value, the current flows and spins around imaginary axis forming a vortex-like structure. In that vortex phase, the external field is only partially cancelled.

These two behaviours have been already observed for real materials, and are of fundamental interest for the superconducting properties. “However, this kind of phenomenon had never been observed with ultracold atoms in optical crystals”, explains Marcos Atala, a scientist in the team of Professor Bloch.

In their 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 lattice 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 resulting periodic structure of light resembles the geometry of simple solid state crystals where the atoms play the role of the electrons, making it an ideal model system to simulate condensed matter physics. In this case, the experimentalists chose a special lattice configuration, which creates an optical crystal with a ladder-like shape (see Fig. 1).

When the electrons in a material are exposed to a magnetic field, they feel the effect of the Lorentz force, which acts perpendicular to their direction of motion, causing them to move in circles. However, the atoms in the optical crystal are electrically neutral and they do not feel that force.

The experimentalists overcome this difficulty by implementing a special laser configuration that simulates the effect of a magnetic field: they used a pair of lasers that give a momentum kick to the atoms when they move from the left to the right leg of the ladder, and give a kick in the opposite direction when they move from the right to the left leg. These kicking lasers simulate the effect of a magnetic field of several thousand Tesla, something that is practically impossible to achieve with real magnetic fields.

The ladder system that the experimentalists realized also presents a Meissner- and a vortex-like phase, with the only difference that the neutral current here does not produce a backaction and thereby a screening of the magnetic field. In order to see the transition between the two phases, the Munich researchers implemented a protocol to measure the current on the individual legs of the ladder.

That current is maximal in the Meissner phase and has a vortex structure in the vortex phase. The measurement idea was to prepare the atoms in either the Meissner or the vortex phase and then to suddenly split the ladder into an array of isolated two-site systems, similar to when a flowing liquid is suddenly stop by an array of barriers. This method allowed the scientist to determine the strength of the current along the legs of the ladder, and they were able to clearly identify a transition from the vortex phase to the Meissner phase.

This experiment marks an important step forward in the simulation of real material properties using ultracold atoms in optical lattices, and opens the path to the observation of many other phenomena like the quantum Hall effect or even the fractional quantum Hall effect if interparticle interactions are present.

Furthermore, by combining this technique with the new available single site resolution, experimentalist could resolve the vortex structure in the ladder locally. “The new experimental probes help us to gain a better understanding of phase transitions and dynamics of quantum matter under the action of extreme magnetic fields”, points out Prof. Immanuel Bloch.

Original publication:

Marcos Atala, Monika Aidelsburger, Michael Lohse, Julio T. Barreiro, Belén Paredes and Immanuel Bloch
Observation of chiral currents with ultracold atoms in bosonic ladders
Nature Physics 2998 (2014), Advance Online Publication

Contact:

Prof. Dr. Immanuel Bloch
Chair of Quantum Optics, LMU Munich
Schellingstr. 4, 80799 München, and
Director at Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching, Germany
Phone: +49 (0) 89 / 32 905 -138
E-mail: immanuel.bloch@mpq.mpg.de

Dr. Belén Paredes
Instituto de Física Teórica UAM/CSIC
C/Nicolás Cabrera 13-15
Cantoblanco
28049 Madrid, Spain
Phone: +34 91 299 9862
E-mail: belen.paredes@csic.es

Dipl. Phys. Marcos Atala
LMU Munich
Phone: +49 89 2180 6133
E-mail: marcos.atala@physik.uni-muenchen.de

Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 (0) 89 32 905 -213
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de/

Further reports about: Highway Max-Planck-Institut Phone Physics Quantenoptik Quantum crystals lattice strength structure transition

More articles from Physics and Astronomy:

nachricht From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison

nachricht Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science

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: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

From rocks in Colorado, evidence of a 'chaotic solar system'

23.02.2017 | Physics and Astronomy

'Quartz' crystals at the Earth's core power its magnetic field

23.02.2017 | Earth Sciences

Antimicrobial substances identified in Komodo dragon blood

23.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>