Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Synthetic magnetism achieved by optical methods

03.12.2009
Technique enables unprecedented insights

For the first time, physicists have used laser light to create "synthetic magnetism," an exotic condition in which neutral atoms suddenly begin to behave as if they were charged particles interacting with a magnetic field -- even though no such field is present and the atoms have no charge.

The achievement provides unprecedented insights into fundamental physics and the behavior of quantum objects, and opens up entirely new ways to study the nature of condensed-matter systems that were barely imaginable before.

There are many phenomena of urgent interest to physicists, such as the action of electrons restrained in two dimensions in a magnetic field, that are difficult to investigate in conventional materials such as semiconductors. Not only is it hard to control the numerous variables involved, but there are always defects and irregularities in the experimental samples. Nonetheless, such research is important both to basic quantum mechanics and to applied fields such as quantum computing and information science. Synthetic magnetism provides a way to model and examine such quantum systems while exercising precision control over the parameters.

"The creation of synthetic magnetic fields for ultracold neutral atoms enables previously impossible experiments in these most quintessential of quantum mechanical systems," says research group leader Ian Spielman, a Fellow of the Joint Quantum Institute and physicist at the National Institute of Standards and Technology (NIST). Spielman and colleagues describe the work in a paper published in the Dec. 3 issue of Nature.

The team began by taking a population of rubidium-87 atoms, decelerating them with a Zeeman slower and then confining them in a magneto-optical trap. The atoms then underwent evaporative cooling in a magnetic trap and then an optical-dipole trap until approximately 250,000 remained at a temperature of about 100 nano Kelvin. Under those ultracold, low-energy conditions, the atoms formed a Bose-Einstein condensate (BEC) ¡V a strange state of matter in which most of the atoms in a group occupy the same minimum-energy quantum state, somewhat as if they collectively constituted a single "super atom."

A small, spatially varying, magnetic bias field was applied across the BEC, producing a gradient that affected the atoms differently depending on their position along one axis of the trap. [See Figure 1.] Then two near-infrared (wavelength, Ć=801.7 nm) laser beams, oriented at 90 degree angles to each other, were aimed into the atoms. The scientists adjusted the beams to have very slightly different frequencies. The cumulative effect of the gradient field and the two laser beams altered the properties of the atoms (in particular, their momentum along one axis) in a way that depended on their location in the trap and their interaction with the beams.

Those differences, the researchers found, could be tuned by making slight changes in the frequencies of the laser beams, in effect conferring a "charge" on sub-populations of the neutral atoms and creating a synthetic magnetic field to which they reacted.

By varying the beams and the gradient, and thus controlling the position-dependent momentum potentials of the atoms, the team observed that ¡V as predicted in a theory paper Spielman had authored earlier this year ¡V atoms at specific points in the trap began to move in a way mathematically equivalent to the way a charged particle would revolve in a magnetic field. The effect caused small quantized vortices of atoms to enter the BEC. [See Figure 2.]

To confirm and measure the magnitude of the phenomenon, the team took pictures of the BEC approximately 25 milliseconds after shutting off all fields and beams in the trap. Images of the expanding atomic cloud clearly showed that when the synthetic magnetism was not present, the atoms in the BEC had the customary distribution. But when the synthetic field was activated, vortices were plainly visible ¡V a clear indication that an optically induced synthetic magnetic field had been created for the first time.

The results are expected to have a substantial impact on various fields of inquiry in quantum science, especially the behavior of electrons confined in different geometries, as they are in real materials. In particular, it will allow researchers to explore how the energy spectrum of electrons in a crystal lattice varies with the magnetic field applied to the system. (This subject produced the now-famous theoretical plot of energy levels called "Hofstadter's butterfly" because of its elegant, wing-like curves.)

In addition, synthetic magnetism should prove valuable in characterizing aspects of the quantum Hall effect, a phenomenon observed in two-dimensional systems of electrons in a magnetic field. In that situation, the electrons naturally tend to follow circular ("cyclotron") orbits; and the energy levels of those orbits are quantized. The National Institute of Standards and Technology uses the quantum Hall effect to define the international standard of resistance.

Further improvements on the synthetic magnetism work, Spielman says, should allow new ways to investigate these and other phenomena.

"By adding an optical lattice potential to our synthetic magnetic field," he says, "we have the opportunity to create both long anticipated systems such as the Hofstadter butterfly -- an iconic pattern of energy levels for non-interacting particles -- and potentially to realize totally new states of matter such as quantum Hall states of bosons."

The research was partially supported by the Office of Naval Research, the Office of the Director of National Intelligence, the Army Research Office and the National Science Foundation through the NSF Physics Frontier Center at the Joint Quantum Institute.

The Joint Quantum Institute (JQI) is a research partnership between University of Maryland (UMD) and the National Institute of Standards and Technology, with the support and participation of the Laboratory for Physical Sciences.

Created in 2006 to pursue theoretical and experimental studies of quantum physics in the context of information science and technology, JQI is located on UMD's College Park campus. For further information, see http://jqi.umd.edu.

Dr. Ian Spielman | EurekAlert!
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht Temperature-controlled fiber-optic light source with liquid core
20.06.2018 | Leibniz-Institut für Photonische Technologien e. V.

nachricht New material for splitting water
19.06.2018 | American Institute of Physics

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: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

What are the effects of coral reef marine protected areas?

21.06.2018 | Life Sciences

The Janus head of the South Asian monsoon

21.06.2018 | Earth Sciences

The world's tiniest first responders

21.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>