Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Swinging of a single atom

Real time optoelectronic feedback stabilizes the orbit of a moving atom

A father pushing his little child on a swing realizes a complex feedback procedure: the signal of the approaching swing is processed in his brain and actuated by his arms pushing with the right power and at the right moment.

Figure: Artist\'s view of the feedback scheme: A single atom placed between two highly reflecting mirrors reveals information about its position by emitting single photons (yellow wave packets). These photons are converted into digital electrical pulses (yellow spheres) and processed in an electronic feedback circuit. The circuit emits an electric current (blue spheres), which alters the intensity of a blue laser (blue valley). This feedback loop swings the atom depending on its measured position. MPQ-Quantum Dynamics

The fast feedback logic developed by a team of scientists around Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics and head of the Quantum Dynamics Division, works quite similar: the system reacts, in real time, on the motion of a single atom orbiting in an optical cavity (Nature, N° 2009-08-10110A, DOI: 10.1038/nature08563).

Individual photons emitted by the atom and carrying information about the atomic position trigger a feedback mechanism that pushes the atom in a direction determined by the experimentalist. This allows him to control the motion of the atom. It increases the time the atom spends in the cavity by a factor of four, but is - even more important - a step towards the exploration of the quantum trajectory of a single atom at a level allowed by Heisenberg's position-momentum uncertainty relation.

The experiment starts by cooling a dilute cloud of neutral rubidium atoms with laser light down to a temperature of a few microkelvin. The cold cloud is then launched - like a fountain - towards a high-finesse optical resonator, made of two highly reflecting mirrors separated by about one tenth of a millimeter. Upon arrival in the resonator, one single atom is captured by suddenly turning on optical tweezers in form of a focused standing laser light wave reflected back and fro between the mirrors. As the trapped atom is sensitive to a variety of different forces, its motion consists of a regular oscillation around the resonator axis superimposed by a strong erratic motion in all directions. This makes the trajectory of the atom unpredictable on time scales not much longer than the oscillation period, typically less than a thousandth of a second.

Now a second laser comes into play that is used as the input signal of the feedback loop. It probes the position of the atom: if no atom is in the resonator, the light of this laser is fully transmitted through both mirrors. If an atom is placed in the center of the resonator the light is blocked and the photon flux drops to rates as low as 0.03 photons per millionth of a second. When the atom moves away from the resonator axis, trying to leave the resonator, more light is transmitted. The position of the atom is thus encoded in the intensity of the transmitted light. To read this information, the photons leaving the resonator are registered by a sensitive detector for two consecutive time intervals of equal duration, the so-called exposure time.

In case more photons are detected in the second time interval than in the first time interval, it is concluded that the atom is trying to escape the resonator. To prevent this, the light intensity of the optical tweezers is ramped up, pushing the atom back to the resonator axis. In case fewer photons are detected in the second time interval, the atom is assumed to approach the cavity axis and the power of the optical tweezers is lowered. This reduces the energy of the atom and leads to an efficient cooling of the atom. The atom can also be heated by inverting the feedback logic. This rapidly expels the atom out of the resonator. "It is important to note that the feedback is triggered by each detected photon. If the number of detected photons goes up from 0 to 1, the intensity of the optical tweezers is ramped up almost immediately, in a time interval that is 70 times shorter than the oscillation period of the atom", Alexander Kubanek, PhD student in the Quantum Dynamics Division explains. "Actually, we have to pay attention that the exposure time is neither too short nor too long", he specifies. "For very short times the information about the position of the atom is insufficient to trigger the desired feedback. If on the other hand the exposure times are too long, the feedback is delayed, leading to a reaction out-of-phase with the atomic oscillatory motion. So we have to choose exposure times that are long enough to give information on the position of the atom, but are yet much shorter than the oscillation period of the atom in the optical tweezers."

The feedback mechanism increases the storage time for a single atom from about six milliseconds without feedback to 24 milliseconds with feedback. Longer storage times exceeding 250 milliseconds are achieved by a more sophisticated technique. But more important than the mere prolongation of the storage times are the quantum mechanical implications of the experiment. "It proves that reliable position information can be obtained by quasi-continuous measurements", Prof. Gerhard Rempe points out. "In the future this might allow us to steer an individual quantum trajectory with a precision ultimately determined by Heisenberg's uncertainty relation or even protect the quantum state of a trapped particle against the disastrous influence of fluctuations stemming from the atom's environment." [Olivia Meyer-Streng]

Original publication:
A. Kubanek, M. Koch, C. Sames, A. Ourjoumtsev, P.W.H. Pinkse, K. Murr, G. Rempe
Photon-by-photon feedback control of a single-atom trajectory
Nature, N° 2009-08-10110A, DOI 10.1038/nature08563, 17.12.2009
Prof. Dr. Gerhard Rempe
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching
Phone: +49 (0)89 / 32905 - 701
Fax: +49 (0)89 / 32905 - 311
Alexander Kubanek
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32905 - 296
Fax: +49 (0)89 / 32905 - 395
Dr. Olivia Meyer-Streng
Press & Public Relations Office
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32905 - 213
Fax: +49 (0)89 / 32905 - 200

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:

Further reports about: DOI Max Planck Institute Optic Quantum laser light optical tweezer single atom

More articles from Physics and Astronomy:

nachricht Matter falling into a black hole at 30 percent of the speed of light
24.09.2018 | Royal Astronomical Society

nachricht Scientists solve the golden puzzle of calaverite
24.09.2018 | Moscow Institute of Physics and 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: Scientists present new observations to understand the phase transition in quantum chromodynamics

The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.

This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.

Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...

Im Focus: Patented nanostructure for solar cells: Rough optics, smooth surface

Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.

"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...

Im Focus: New soft coral species discovered in Panama

A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.

Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...

Im Focus: New devices based on rust could reduce excess heat in computers

Physicists explore long-distance information transmission in antiferromagnetic iron oxide

Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.

Im Focus: Finding Nemo's genes

An international team of researchers has mapped Nemo's genome

An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

"Boston calling": TU Berlin and the Weizenbaum Institute organize a conference in USA

21.09.2018 | Event News

One of the world’s most prominent strategic forums for global health held in Berlin in October 2018

03.09.2018 | Event News

4th Intelligent Materials - European Symposium on Intelligent Materials

27.08.2018 | Event News

Latest News

Matter falling into a black hole at 30 percent of the speed of light

24.09.2018 | Physics and Astronomy

NASA balloon mission captures electric blue clouds

24.09.2018 | Earth Sciences

New way to target advanced breast cancers

24.09.2018 | Health and Medicine

Science & Research
Overview of more VideoLinks >>>