Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Stopping Molecules with a Centrifuge

07.01.2014
A novel deceleration technique brings fast continuous beams of polyatomic polar molecules almost to a halt

Does the electron possess an electric dipole moment? Will it be possible to achieve perfect control over chemical reactions between polyatomic molecules, or can one envisage quantum simulations and quantum computation with cold polar molecules?


Fig. 1: On a fast rotating disc, an electric quadrupole guide forces the molecules to move towards the rotation axis. As the molecules have to fight against the centrifugal force on their way, they loose kinetic energy and are slowed down to almost a complete halt.
Graphic: MPQ, Quantum Dynamics Division

The fast-growing investigation of cold polar molecules holds promise for delivering answers to these long-standing questions that concern fundamental physics as well as future applications. Producing abundant samples of cold polyatomic molecules from thermal ensembles, however, is a formidable challenge. A key method for obtaining cold molecules is the deceleration of molecular beams.

This has been achieved so far only in the pulsed mode, with a very low duty cycle. Thus the hitherto-implemented techniques cannot make use of the intrinsically high flux delivered by the available continuous molecular sources. To utilize the full potential of such sources, a continuous deceleration is warranted. Towards this end, a team of scientists in the Quantum Dynamics Division of Professor Gerhard Rempe at the Max-Planck-Institute of Quantum Optics has now developed a versatile deceleration technique dubbed centrifuge decelerator, which makes possible for the first time the deceleration of continuous beams of polyatomic polar molecules (PRL, DOI: 10.1103/PhysRevLett.112.013001, 6 January 2014).

The stunning advances in atomic physics and quantum optics over the past three decades ensued to a great extent from the development of efficient laser cooling and deceleration techniques. Compared to atoms, molecules are more complex objects and possess a more involved internal-energy structure: in addition to the electronic states, molecules have also vibrational and rotational states. For this reason, the laser cooling and deceleration methods, which are the workhorses in atomic physics, are not applicable to molecules, in particular polyatomic ones.

A natural way to decelerate a molecule (as any other object) is to make it climb up a potential hill, thereby transforming its kinetic energy into a potential one. Such a hill can be provided through the interaction of a molecule with an external field, be it electric, magnetic or gravitational. For instance, the application of electric fields makes use of the dipole moment that a large number of molecules (unlike atoms) possess because of an uneven charge distribution within the molecule. The dipole moment interacts with the external electric fields, and by making the molecules move from a region with a weaker field to a region with a stronger field they lose kinetic energy. In a similar fashion magnetic molecules can be decelerated with external magnetic fields.

“The disadvantage of these two methods is that for most molecules of interest the typical height of electric or magnetic hills is of the order of 1 Kelvin, whereas molecules from our liquid-nitrogen-cooled source have initial kinetic energies of the order of 100 Kelvin”, Dr. Sotir Chervenkov, leader of the experiment, explains. “Hence, the molecules have to climb up a sequence of around hundred hills. This implicates that one has to apply this process many times in succession, which leads to operation in the pulsed regime.”

To circumvent this limitation, one has to provide a sufficiently high potential (~100 K) in order to decelerate molecules in one stretch. Such a high potential is provided by the gravitational field of the Earth, for instance. Simple calculations, however, show that for a molecule to be decelerated from around 200 metre per second down to a trappable velocity of around 20 metre per second it has to fly upwards in the gravitational field of the Earth for 2000 metres, which renders such an experiment impossible or at least very demanding. The alternative is to artificially create an analogue of a gravitational field in the laboratory.

“We are the first group worldwide which exploits this possibility”, points out Dr. Chervenkov. “Everyone who has been on a merry-go-round has experienced the outward force, which exists in a rotating frame. This force can be much larger than the gravitational force of the Earth, and is exploited in centrifuges for a multitude of biological, chemical, medical and industrial applications.” Xing Wu, a doctoral candidate who performed the first measure-ments, adds: “Now we employ a rotating frame for a conceptually different purpose, namely to decelerate a gas of neutral molecules from about 200 metre per second to almost a standstill.” Martin Zeppenfeld, who initially proposed the idea, further elucidates the deceleration mechanism: “First the molecules propagate around the periphery of the centrifuge in a stationary storage ring with a diameter of 40 cm composed of two static and two rotating electrodes. Then a rotating spiral-shaped electric quadrupole guide picks up the molecules almost at any point around the storage ring and whirls them to the rotation axis. Thus the centrifuge deceleration is a two-step process: the velocity of the molecules decreases first upon their transition from the laboratory into the rotating frame, and further, while propagating in the rotating guide, as they are forced to climb up a huge potential hill and are continuously slowed down, eventually reaching the rotation axis at close-to-zero velocity.”

The MPQ team demonstrated the capabilities and the universality of the new technique by deceleration of three species with different masses and a dipole moment of the order of 1.5 Debye, CH3F, CF3H, and CF3CCH. In their experiment the scientists vary both the rotation speed of the disc and the voltage at the quadrupole guide. For optimal conditions they achieved continuous output beams with intensities of several billion molecules per square-millimetre per second for molecules with kinetic energies below 1 Kelvin.

“Novel features of the centrifuge decelerator are its continuous operation, high beam intensity, applicability to a large set of molecules, and ease of operation. Therefore it has the potential to become an extremely valuable method in the cold-molecule research,” Professor Gerhard Rempe points out. “The universality of the centrifugal force might also enable one to slow down atoms that cannot be laser-cooled, and possibly even cold neutrons.”

Accumulation of centrifuge-decelerated molecules in an electric trap and further cooling them via the recently demonstrated technique of Sisyphus cooling developed in the same group at the MPQ might allow for a dramatic increase of the phase-space density for controlled collision experiments with polyatomic molecules and pave the way to achieving quantum degenerate regimes with polar molecules. [SC/OM]

Original publication:

S. Chervenkov, X. Wu, J. Bayerl, A. Rohlfes, T. Gantner, M. Zeppenfeld, and G. Rempe
Continuous Centrifuge Decelerator for Polar Molecules
Physical Review Letters, DOI: 10.1103/PhysRevLett.112.013001, 6 January 2014
Contact:
Prof. Dr. Gerhard Rempe
Director at Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -701 /Fax: -311
E-mail: gerhard.rempe@mpq.mpg.de
Dr. Sotir Chervenkov
Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -244 /Fax: -395
E-mail: sotir.chervenkov@mpq.mpg.de
Dr. Olivia Meyer-Streng
Press & Public Relations
Max-Planck-Institute of Quantum Optics
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -213
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht Interstellar seeds could create oases of life
28.08.2015 | Harvard-Smithsonian Center for Astrophysics

nachricht Draw out of the predicted interatomic force
28.08.2015 | Hiroshima 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: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Interstellar seeds could create oases of life

28.08.2015 | Physics and Astronomy

An ounce of prevention: Research advances on 'scourge' of transplant wards

28.08.2015 | Health and Medicine

Fish Oil-Diet Benefits May be Mediated by Gut Microbes

28.08.2015 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>