Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Observing Quantum Particles in Perfect Order

19.08.2010
Scientists at the Max Planck Institute of Quantum Optics succeed in recording single-atom resolved images of a highly correlated quantum gas.

Ultracold atoms in optical lattices have evolved in the last years into an interdisciplinary tool for many-body solid state and quantum physics. But so far only limited possibilities were available to manipulate and to image the quantum gas on a microscopic scale.


In a BEC the atom number density shows large fluctuations from lattice site to lattice site (left). In the Mott insulator state (middle) the atom number is almost perfectly constant. For higher particle numbers the characteristic shell structure evolves (right). MPQ, Quantum Many-Body Division

For the first time a team around Stefan Kuhr and Immanuel Bloch at MPQ has now succeeded in observing – atom by atom, lattice site by lattice site – such a strongly correlated system (Nature, 18 August 2010, DOI 10.1038/nature09378). The physicists saw that under certain conditions the atoms in the optical lattice arrange in a very regular distribution, with a fixed number of atom per lattice site. This is an important precondition for using these systems as quantum registers with individually addressable quantum bits in future quantum computers.

In their experiment, the physicists deal with a cloud of thousands “bosonic” rubidium atoms. Bosons behave very socially as they aim for the same quantum state at very low temperatures, forming a Bose-Einstein condensate. These ultracold atoms are almost at rest which makes them very sensitive to external light fields. This effect is used to place the atoms in a regular lattice structure. The scientists superimpose crosswise standing laser light waves from different directions, thus creating an optical lattice, a periodic crystal made of dark and bright areas. The resulting light field resembles an egg carton: the dips, which correspond to the bright areas, are energetically favoured. These are the sites where the rubidium atoms like to settle down.

Depending on the lattice height, i.e. the light intensity, correlations between the particles may lead to completely different properties of the whole system. For low intensities the particles are allowed to “tunnel” to their neighbouring sites. The ensemble then represents a superfluid. If, on the other hand, the interactions between the particles dominate at larger lattice depth, the particles are fixed to the lattice sites, and the system evolves into a so-called Mott-insulator (named after the British physicist and Nobel prize winner Sir Neville F. Mott).

According to model calculations, in a BEC the number of atoms varies from lattice site to lattice site, whereas it should approach (for very low temperatures) a constant value in the Mott-insulator case. Now the scientists have been able to directly observe this behaviour experimentally. “We succeeded in imaging single atoms on their individual lattice sites This is a really sensational result”, Dr. Stefan Kuhr, the leader of the project, explains enthusiastically. “As is commonly done we cool the atoms using laser beams. At the same time however we use the fluorescence photons emitted in this process for observing the atoms with a specially developed microscope. This way it was possible to count the atoms on each lattice site. Recording snap shots of atom distributions in the quantum liquid, we were able to detect even single defects and monitor their proliferation when the temperature of the gas was increased.”

Varying particle number and temperature of the quantum gas, the physicists counted the number of atoms per lattice site in a series of systematic measurements. As expected for the BEC the atom density exhibited large number fluctuations. On the other hand, for the Mott insulator an almost perfect structure with a very low defect density was obtained (see images).

The MPQ team even resolved the shell structure which is characteristic of a Mott insulator for large particle numbers (see figure). This structure is caused by the fact that the optical lattice is not flat, but its outer wings point upwards, following the Gaussian profile of the laser intensity. Lattice sites on the outer edge are therefore energetically disfavoured and not occupied before the inner ones have all been taken. From the outside to the inner core the atom number per site increases in a stepwise manner. Pairs of atoms however get immediately lost due to inelastic collisions induced by the irradiated laser beams. Therefore the shell structure appears as alternating bright and dark rings.

A Mott insulator with exactly one atom per lattice site represents a very promising candidate for a quantum register of up to a few hundred atomic quantum bits. “Yet it has to be shown that we are really able to manipulate each individual atom”, Dr. Kuhr explains. “This is a crucial requirement for encoding and reading out quantum bits. We are now at the beginning of setting up the first experiments of that kind.”

Ultracold quantum gases are not only suited for applications in future quantum computers but can also serve as models for condensed matter physics. Here the atoms in the optical lattice play the role of the electrons in the solid state crystal. Investigations along these lines may lead to a deeper understanding of unusual magnetic and electric phenomena, e.g. high-Tc-superconductivity , and may pave the way towards “tailor-made” materials. Olivia Meyer-Streng

Original publication:
Jacob F. Sherson, Christof Weitenberg, Manuel Endres, Marc Cheneau, Immanuel Bloch and Stefan Kuhr
Single-Atom Resolved Fluorescence Imaging of an Atomic Mott Insulator
Nature, 18 August 2010, DOI 10.1038/nature09378
Contact:
Dr. Stefan Kuhr Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching b. München
Germany
Phone: +49 89 32905 738
e-mail: stefan.kuhr@mpq.mpg.de
Prof. Dr. Immanuel Bloch
Chair of Experimental Physics
LMU Munich, Schellingstr. 4
80799 München, Germany, and
Max Planck Institute of Quantum Optics
Phone: +49 89 32905 138
e-mail: immanuel.bloch@mpq.mpg.de

Dr. Olivia Meyer-Streng | idw
Further information:
http://www.mpq.mpg.de/
http://www.quantum-munich.de

More articles from Physics and Astronomy:

nachricht Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

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: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>