Habilitationsprojekt von Dr. Dongdong Zhang

”A traveling wave Zeeman decelerator for precision measurements and ion-neutral chemistry at very low temperatures”

For the past century, scientists have been pursuing the goal of reaching ever lower temperatures towards absolute zero. Each step on this journey led to the discovery of fascinating new physics. Lowering the temperature down into the kelvin regime was rewarded by the observation of superconductivity by Heike Kamerlingh Onnes in 1911. Observation of these new phenomena at the lowest temperature found in our universe is just the beginning of the story. The advent of laser cooling of atoms in the 1980s opened up a completely new realm with temperatures down to several microkelvins (six orders of magnitude lower than the coldest spot in our universe). This provides the possibility to explore low-temperature phenomena in the gas phase and revolutionized atomic physics, e.g., today’s most accurate time standard is made possible by an atomic fountain, the collisions between atoms at very low temperatures reveal the quantum wave nature of particles and further cooling of atoms down to the nanokelvin regime provides the necessary conditions to realize Bose-Einstein condensates, which was predicted theoretically 70 years ago.

The achievements in low-temperature atomic physics intuitively lead to the question: can one achieve similarly low temperatures in gas-phase molecules and what does one expect to happen to molecules at such low temperatures? Cold molecules may revolutionize physical chemistry and few-body physics, provide techniques for probing new states of quantum matter, allow for precision measurements of both fundamental and applied interest, and enable quantum simulations of condensed-matter phenomena. Unlike in atoms, in molecules the internal energy structures are way more complicated. As a consequence, alternative methods based on the interaction between molecules and external fields (electric, magnetic and radiation fields) are required to cool down molecules.

The objective of the current proposal is to advance the development of techniques to realize cold molecules in large quantities. A new type of decelerator has been designed and constructed by the applicant. This machine utilizes state-of-the-art techniques to generate complex time-dependent magnetic fields to manipulate molecules possessing magnetic dipole moments. It generates a moving magnetic trap. By catching molecules as they fly into the trap and decelerating the trap, cold molecules will be generated at large number densities and high efficiency.

Thanks to the FAG-Basel funding, I can explore new frontiers in molecular and chemical physics along several lines with my proposed decelerator: Our decelerator is a new technique to generate cold molecules. The advantages of our decelerator over existing decelerators include that it provides a unique rotating trap which offers more flexibilities to control. This will enable us to generate samples with vastly increased densities, opening up new possibilities for their cooling, collisions and spectroscopic measurement, which has not been possible with the previous low density sources. The proposed deceleration technique will improve the accuracy of molecular structure measurements. This will lead to a better experimental and theoretical understanding of the mechanisms involved in the molecular system and will supplement the fundamental data on molecules. The proposed decelerator will also open up a completely new research area. Cold collision and cold chemistry between trapped paramagnetic atoms or molecules and trapped atomic and molecular ions can be studied at low temperatures with very high collision energy resolution. This will reveal the quantum nature of gas-phase chemical reactions at low temperatures.

Dr. Dongdong Zhang