Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Observing Quantum Particles in Perfect Order

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
Dr. Stefan Kuhr Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching b. München
Phone: +49 89 32905 738
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

Dr. Olivia Meyer-Streng | idw
Further information:

More articles from Physics and Astronomy:

nachricht First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

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: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>



Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

More VideoLinks >>>