Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Interference at a Double Slit Made of Two Atoms


MPQ scientists observe unusual interference phenomena by scattering laser light from two atoms trapped inside an optical resonator

The investigation and exploitation of light-matter-interaction in optical resonators is one of the central research topics in the Quantum Dynamics Division of Professor Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics in Garching.

Figure 1: Resonant laser light (red arrow) is being scattered from two single atoms. The effects that arise due to interference (here shown in an artist’s view) are determined by the relative spatial phase of the atoms and the interaction with the light mode of the optical resonator (mirrors in grey). Lower left: fluorescence image of two rubidium atoms. (Graphic: Andreas Neuzner, MPQ)

A couple of years ago, the team succeeded in creating single-photon emitters using single atoms stored in optical resonators. The stationary atoms can, for example, serve as nodes for the exchange of quantum information in a long-distance quantum network. Now, the scientists went one step further. They trapped a pair of atoms with well-defined relative positions in such a resonator and scattered light from this “double slit”.

They observed interference phenomena that contradict well-established intuition. These results were enabled by the development of a technique that allows for position control of the atoms with an accuracy well below the wavelength of the scattered light. One motivation for this experiment is to better understand fundamental aspects of cavity quantum electrodynamics.

Furthermore, the technique paves the way for studying new concepts of entanglement generation between quantum bits and thus opens up new perspectives for quantum information processing (Nature Photonics, AOP, 29 February 2016, DOI:10.1038/nphoton.2016.19).

Key element of the experimental set-up is an optical resonator consisting of two highly-reflecting mirrors spaced by 0.5 mm. Inside the cavity, a so-called optical lattice is generated by crossing two retro-reflected laser beams, one oriented orthogonal to and the other along the resonator axis. The resulting light pattern of bright and dark spots resembles a checker board with a period of about half a micrometre. These spots define lattice sites at which the atoms can be trapped and where they are localized to about 25 nanometres.

At first, a couple of rubidium atoms, precooled to very low temperatures, are loaded into the optical lattice. By detecting their fluorescence light via a high-resolution microscope objective, the atoms can be identified as individual light spots. Excess atoms are subsequently removed by individually heating them up with a resonant laser beam, until only a pair of atoms with the desired spacing remains. “This is the “double-slit” from which the resonant laser light, propagating transversally through the resonator, is scattered”, explains Andreas Neuzner, who performed this experiment as part of his doctoral studies.

„Interference can only be observed if the phase relation between the two light sources is fixed“, explains Dr. Stephan Ritter, another scientist on the experiment. “In order to investigate the interference as a function of the phase, we have to know the position of the atoms with a precision well below the wavelength of 780 nanometres.“ Although the resolution of the imaging system limits the size of the atom images to 1.3 micrometres, the scientists can localize the emitting atoms with an accuracy of 70 nanometres and can thereby assign their position to a particular lattice site. Therefore, the distance between two atoms, typically about 10 micrometres, is precisely known.

The resonator favours emission along its axis and enhances the interaction between the atoms and the scattered light, which is reflected multiple times between the mirrors. The light power leaking through one of the mirrors – i.e. the photon rate – is recorded as a function of the relative phase of the two atoms.

The observed interference pattern displays several intriguing features that are not expected in the simpler picture of two classical dipoles in free space. First, in the case of in-phase (constructive) interference, the intensity is only a factor of 1.3 larger than the rate observed for a single atom, whereas a fourfold larger signal is expected for the simpler picture. This phenomenon goes back to the various light fields inside the resonator that have to be taken into account. In contrast to the classical double-slit experiment, not only the phase relation between the scattered light waves matters. It is rather the superposition of the scattered light with the light field of the resonator that in the end leads to an intensity reduction in the field maxima.

The second feature occurs for out-of-phase (destructive) interference. Here, the photon rate drops below the value measured for a single atom, but does not go to zero as one would expect intuitively. Strikingly, extremely strong intensity fluctuations are observed, so-called photon bunching. “This phenomenon arises, because in the case of destructive interference, the atoms can emit photons only pairwise and at the same time into the resonator”, explains Andreas Neuzner.

„In this experiment we have combined three key techniques for the first time: Using an optical lattice, we position the atoms with high accuracy and then localize them with a high-resolution microscope. The interaction with the resonator enables directed detection of the scattered light“, says Stephan Ritter. “The newly developed techniques are essential for future experiments aiming to explore collective radiation effects predicted for multi-atom systems“, resumes Prof. Gerhard Rempe. “On the other hand, they offer the possibility to implement novel protocols for quantum information processing with several quantum bits.”
Olivia Meyer-Streng

Original publication:
A. Neuzner, M. Körber, O. Morin, S. Ritter and G. Rempe
Interference and dynamics of light from a distance-controlled atom pair
in an optical cavity
Nature Photonics, AOP 29 February 2016, DOI:10.1038/nphoton.2016.19

Prof. Dr. Gerhard Rempe
Director at the Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1, 85748 Garching, Germany
Phone: +49 (0)89 / 32 905 - 701

Dr. Stephan Ritter
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 728

Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 213

Dr. Olivia Meyer-Streng | Max-Planck-Institut für Quantenoptik

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>



Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

More VideoLinks >>>