Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New paths for generation of ultracold molecules

11.02.2016

Scientists at MPQ produce an extremely cold gas of organic polar molecules

The study of ultracold molecules is a science of its own. Ultracold molecules provide the possibility to investigate fundamental chemical processes or to explore physics beyond the standard model of particle physics.


Fig. 1: Left: Illustration of the various processes that take place during Sisyphus cooling of polar molecules. Right: Sketch of the experimental setup.

Graphic: MPQ, Quantum Dynamics Division


Fig. 2: Integral of the kinetic energy distribution of formaldehyde molecules at the end of the cooling cycle.

Graphic: MPQ, Quantum Dynamics Division

The only snag is the fact that molecules are very difficult to cool down to really low temperatures because of their manifold vibrational and rotational states. A team of scientists led by Dr. Martin Zeppenfeld from the Quantum Dynamics Division of Prof. Gerhard Rempe at the Max Planck Institute of Quantum Optics in Garching has now made a virtue of necessity: the so-called optoelectrical Sisyphus technique, developed in the group, exploits the polarity of formaldehyde molecules, while reaching temperatures as low as 420 micro-Kelvin (PRL, 10 February 2016, DOI:10.1103/PhysRevLett.116.063005).

As a result of the cooling process, not only the temperature but also the entropy – a measure of thermodynamic disorder – of the gas is significantly reduced. The system thereby approaches the regime where it has to be described by the laws of quantum physics. “We have reached a point where we can proceed with further experiments that will lead to new fundamental insights into the behaviour of molecular many-body systems,” Professor Rempe says. “For example, we envision the investigation of collision processes or of molecular spectra. These are of particular interest because formaldehyde plays a key role in chemistry in interstellar space.”

The central part of the experiment is an electrostatic trap, made of two capacitor plates spaced by three millimetres. The plates are covered by microstructure electrodes between which high voltages are applied. The resulting potential is similar to a “bath tub”, with a small homogeneous field in the centre of the trap and a steep rise of the field at the edges.

A cloud of formaldehyde molecules (H2CO), precooled to less than 1 Kelvin (minus 273 Grad Celsius), is loaded into this potential. The mechanism of the subsequently applied relatively new cooling technique relies on the fact that these molecules exhibit a permanent electric dipole moment (i.e. the negative charge is shifted towards the oxygen atom). Depending on the orientation of its dipole with respect to the electric field a molecule is either strongly trapped (anti-parallel orientation), weakly trapped (inclined) or, in the case of parallel alignment, not trapped at all, which means that the molecule gets lost.

Inside the trap the particles climb up the potential hill at the edges until their kinetic energy is almost completely converted into potential energy. At this point RF-radiation changes the dipole orientation of a particular molecule into a more weakly trapped state. (The RF-radiation is only resonant to transitions in the high electric fields that are prevalent at the edges of the trap.) As this state corresponds to a lower potential energy, the particle regains a smaller amount of kinetic energy when it rolls back into the centre of the trap (see fig. 1).

Repeating this process requires the molecule to be brought back into the strongly trapped state once it has reached the bottom of the trap. This is done by exciting the molecule, by infrared laser light, into a vibrational state that spontaneously decays into the ground state. During this transition the dipole possibly flips back into antiparallel alignment.

“The rate of the cooling procedure depends on the rate of this spontaneous decay. In particular it is very important that it proceeds much faster than the transition induced by the RF-radiation,” points out Alexander Prehn, a doctoral candidate on the experiment. “Each time the cycle is repeated the molecules loose kinetic energy; and because they have to climb up the potential hill again and again, the method is named after the Greek hero Sisyphus.”

A timespan of about 50 seconds (15 to 20 cycles) is sufficient to cool the molecular cloud down to a temperature of around 420 micro-Kelvin. To determine the final temperature distribution, a series of measurements is performed where the ensemble is irradiated with radio waves of a different frequency each time. All molecules that can mount the potential hill up to a certain height (which depends on the frequency) or above are transferred into non-trapped states and get lost. The remaining molecules of lower kinetic energy are counted. This way a distribution of the kinetic energy can be deduced (see fig. 2).

That way the team has produced the largest ensemble of ultracold molecules ever and has thus set a new record. In addition, by applying the right kind of infrared and microwave radiation, they make 80 percent of the molecules end up in the same internal rotational state. “It is of great importance that during all these cooling steps the entropy of the ensemble has been reduced,” Martin Zeppenfeld, leader of the project, points out. “With the help of optoelectrical Sisyphus cooling we have increased the phase-space density by a factor of 10 000 which proves the usefulness of the technique. The final state stands out due to its greatly reduced thermodynamic disorder. This provides the possibility to investigate collisions between the molecules or, in future experiments, to explore collective quantum many-body phenomena. New perspectives also exist in the field of spectroscopy.”

“Laboratory experiments with formaldehyde at low temperatures are particularly interesting since formaldehyde plays a key role in chemistry at low temperatures in interstellar space. It is regarded as a fundamental building block of all more complex organic compounds.” Martin Ibrügger, a doctoral candidate on the experiment, adds. The cooling method can be applied to different molecular species, and it could be further improved to reach even lower temperatures. “As one of the next steps we can also try to continue with other cooling techniques such as evaporative cooling. This should allow the nano-Kelvin regime to be reached which is necessary for the formation of a Bose Einstein Condensate.” Rosa Glöckner, a doctoral candidate on the experiment, explains. “Our result is thus an important step on the way to producing quantum-degenerate gases made of poly-atomic molecules.” Olivia Meyer-Streng

Original publication:
Alexander Prehn, Martin Ibrügger, Rosa Glöckner, Gerhard Rempe, and Martin Zeppenfeld
Optoelectrical cooling of polar molecules to sub-millikelvin temperatures
Physical Review Letters, 10 February 2016, DOI:10.1103/PhysRevLett.116.063005

Contact:

Prof. Dr. Gerhard Rempe
Director at Max Planck Institute of Quantum Optics
Hans-Kopfermann-Str. 1
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 - 701
E-mail: gerhard.rempe@mpq.mpg.de

Dr. Martin Zeppenfeld
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 726
E-mail: martin.zeppenfeld@mpq.mpg.de

Alexander Prehn
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 614
E-mail: alexander.prehn@mpq.mpg.de

Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 (0)89 / 32 905 - 213
E-mail: olivia.meyer-streng@mpq.mpg.de

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

More articles from Physics and Astronomy:

nachricht Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa

nachricht Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik

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: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>