We present an experimental realization of a moving magnetic trap decelerator, where paramagnetic particles entrained in a cold supersonic beam are decelerated in a co-moving magnetic trap.Our method allows for an efficient slowing down of both paramagnetic atoms and molecules to near stopping velocities.We show that under realistic conditions we will be able to trap and decelerate a large fraction of the initial supersonic beam.We present our first results on deceleration in a moving magnetic trap by bringing metastable neon atoms to near rest.Our estimated phase space volume occupied by decelerated particles at a final velocity of 50 m s -1 shows an improvement of two orders of magnitude as compared to currently available deceleration techniques.Cold chemistry (at temperature of ∼1 K) is a fast developing field with many interesting theoretical predictions yet only a few experiments [1][2][3][4].It has been predicted that in the cold chemistry regime, reactions might proceed through resonance states [5] and both reaction rate and path could be controlled [6] via external magnetic or electrostatic fields.Low-temperature chemistry is not limited to artificially created conditions alone but occurs naturally at the low temperature of interstellar space [7] and the atmospheres of remote planets and moons [8].It is anticipated that cold chemistry will follow the enormous progress in molecular chemistry that was spurred by the advent of supersonic beams more than half a century ago [9].However, the progress in experimental cold chemistry is rather slow partly due to the absence of a general method of atomic and molecular cooling.Although the low-temperature environment created within a supersonic expansion has been used to observe many reactions [10], a direct 1 Author to whom any correspondence should be addressed.
We present an experimental realization of a moving magnetic trap decelerator, where paramagnetic particles entrained in a cold supersonic beam are decelerated in a co-moving magnetic trap.Our method allows for an efficient slowing down of both paramagnetic atoms and molecules to near stopping velocities.We show that under realistic conditions we will be able to trap and decelerate a large fraction of the initial supersonic beam.We present our first results on deceleration in a moving magnetic trap by bringing metastable neon atoms to near rest.Our estimated phase space volume occupied by decelerated particles at a final velocity of 50 m s -1 shows an improvement of two orders of magnitude as compared to currently available deceleration techniques.Cold chemistry (at temperature of ∼1 K) is a fast developing field with many interesting theoretical predictions yet only a few experiments [1][2][3][4].It has been predicted that in the cold chemistry regime, reactions might proceed through resonance states [5] and both reaction rate and path could be controlled [6] via external magnetic or electrostatic fields.Low-temperature chemistry is not limited to artificially created conditions alone but occurs naturally at the low temperature of interstellar space [7] and the atmospheres of remote planets and moons [8].It is anticipated that cold chemistry will follow the enormous progress in molecular chemistry that was spurred by the advent of supersonic beams more than half a century ago [9].However, the progress in experimental cold chemistry is rather slow partly due to the absence of a general method of atomic and molecular cooling.Although the low-temperature environment created within a supersonic expansion has been used to observe many reactions [10], a direct 1 Author to whom any correspondence should be addressed.
The long standing goal of chemical physics is finding a convenient method to create slow and cold beams intense enough to observe chemical reactions in the temperature range of a few Kelvin. We present an extensive numerical analysis of our moving magnetic trap decelerator showing that a 3D confinement throughout the deceleration process enables deceleration of almost all paramagnetic particles within the original supersonic expansion to stopping velocities. We show that the phase space region containing the decelerating species is larger by two orders of magnitude as compared to other available deceleration methods.
Supersonic beams provide a source of cold atoms where laser cooling is not applicable. Although the atoms' temperature in the co-moving frame is in the subkelvin range their velocity is on the order of several hundreds of meters per second. This thesis describes the experimental realization of a novel method to slow atoms and molecules with permanent magnetic moments using pulsed magnetic fields. The method is suitable for most elements since most atomic species are paramagnetic, and can also be applied to certain molecules, as well as electronically excited metastable states and most radicals. We show the slowing of metastable neon in a proof of principle experiment where the mean velocity is reduced from 461.0[plus or minus] 7.7 m/s to 403 [plus or minus]16 m/s in 18 stages. A second setup with 64 stages is now operating and allows us to stop metastable neon in principle. Preliminary results showing slowing from 447[plus or minus]3m/s to 136[plus or minus]5m/s with an efficiency of up to 3.9% are included here, and the slower has been shown to generate atoms as slow as 50 m/s. We find that the slowing efficiency depends strongly on the switching phase. In addition to the experimental results described above, we present simulations of a moving trap which allows trapping and decelerating at the same time.
A unique property of Zeeman effect based manipulation of paramagnetic particle's motion is the ability to control velocities of both atoms and molecules. In particular the moving magnetic trap decelerator is capable of slowing and eventually trapping mixtures of both cold atoms and cold molecules generated in a supersonic expansion. Here we report the deceleration of molecular oxygen together with metastable argon atoms. The cold mixture with temperature below 1 K is slowed from an initial velocity of 430 m s −1 down to 100 m s −1 . Our decelerator spans 2.4 m and consists of 480 quadrupole traps. Our results pave the way for the study of sympathetic cooling of molecules by laser cooled atoms.
We demonstrate simultaneous deceleration and trapping of a cold atomic and molecular mixture. This is the first step towards studies of cold atom-molecule collisions at low temperatures as well as application of sympathetic cooling. Both atoms and molecules are cooled in a supersonic expansion and are loaded into a moving magnetic trap that brings them to rest via the Zeeman interaction from an initial velocity of 375 m/s. We use a beam seeded with molecular oxygen, and entrain it with lithium atoms by laser ablation prior to deceleration. The deceleration ends with loading of the mixture into a static quadrupole trap, which is generated by two permanent magnets. We estimate 10^{9} trapped O_{2} molecules and 10^{5} Li atoms with background pressure limited lifetime on the order of 1 sec. With further improvements to lithium entrainment we expect that sympathetic cooling of molecules is within reach.
Research of cold and ultracold molecules is currently a burgeoning field in experimental and theoretical physics. New experimental techniques, involving an increasingly large set of molecule types under high levels of control, are currently opening up new avenues of research with a vast array of potential applications. From understanding the role of quantum mechanics in molecular scattering and cold chemistry, to testing the fundamental symmetries of nature and realizing quantum computing with dipolar molecular qubits, experiments are accessing regimes not dreamed of even a few years ago. Theoretical interest and computing capabilities are also at an all time high, spurred on by the possibility of creating ultracold dipolar gases as tunable realizations of strongly interacting quantum Hamiltonians, creating exotic phases of matter, and the investigation of controlling molecular interactions with applied electromagnetic fields.\nLess than a decade ago, cold molecule experiments had seemingly reached a technological plateau, being capable of creating moderate densities of 106-107 molecules/cm3 at temperatures of 10-100 mK. With many applications requiring colder temperatures and higher densities, the field was ripe for new advances. Today, via a plethora of methods such as direct molecular laser cooling, electro-optical cooling, magneto- and photo-association, and new molecular beam deceleration techniques, the field is just beginning to have the tools capable of producing truly interesting systems for study.\nThis work will discuss a couple of major steps taken in the direction of achieving scientific goals using cold molecules. The first experimental advancement discussed will be the development of a co-trap environment for studying interactions and collisions between ultracold atoms and Stark decelerated cold polar molecules. In this experiment, rubidium atoms are trapped using magnetic fields, and ammonia atoms are decelerated and trapped using electric fields. The two traps are spatially overlapped in order to investigate inter-species interactions. The co-trap environment provides exceedingly long interaction times, many orders of magnitude longer than typical beam-based interaction studies. As a result, it provides extremely high sensitivity to weak interaction mechanisms. The second experimental advancement discussed will be the development and construction of a new style of Stark decelerator, capable of producing much larger densities of cold molecules. This apparatus has the potential to expand the realm of possible experiments with chemically interesting species, and provide an unprecedented amount of control over molecular beams and traps. The gains haven't come easily though, as a new class of custom high-voltage amplifiers have needed to be developed. This part of the experiment alone took approximately two years of consistent effort to bring to fruition. After many years of development, this experiment is poised to come online, finally fulfilling its potential.
This dissertation describes a general approach of generating a high flux of cold atoms that can be confined in a magneto-optical trap. As an alternative to the state-of-the-art laser cooling method, this approach widens our ability to cool and control atoms without relying on a specific atomic transition and availability of laser. In this dissertation I will discuss the design, construction of the experiment and characterization of a pulsed cold atom source in detail. This work is based on a new paradigm: entrainment of atoms in the carrier gas of a supersonic beam, followed by the magnetic deceleration and trapping. Our methodology is based on the supersonic beam created by the expansion of a dense carrier gas from a pulsed release of gas through a small aperture. Cold noble gas emerging from this pulsed high pressure supersonic nozzle acts as a carrier, into which atoms of interest are then entrained. In our studies with the lithium atoms, up to 10¹¹ atoms per pulse could be entrained into a supersonic beam of helium at a translation temperature of below 100 mK. The supersonic valve is typically operated at a rate of below 1 Hz in the experiment. A much larger flux can be achieved at a higher repetition rate. These atoms are moving at a speed of 500 ms⁻¹ and need to be decelerated almost to a complete stop, in order to be trapped and cooled to quantum degeneracy. A 2.5-meter long moving-trap magnetic decelerator with 480 coil pairs was built and characterized. Atoms moving at a speed around 500 ms⁻¹ were trapped and decelerated to various final velocities ranging from 400 ms⁻¹ to 50 ms⁻¹, at a resulting temperature of 30 mK and a flux of 10⁸ ~ 10⁹ atoms per pulse. This whole process takes place within only 10 ms, at a repetition rate of 100 Hz 10¹⁰ ~ 10¹¹ atoms can be delivered per second. This approach is very general compared to the laser cooling, since most atoms in the periodic table have a magnetic moment in their ground state or can be optically pumped to a long-lived para-magnetic metastable state. In this dissertation, I show the working principle of each component of our experiment and characterize the atom beam at multiple stages. I describe in detail the construction and optimization of our magnetic decelerator, and demonstrate the control and monitoring system with the experiment results. Also implemented in this work is a flexible laser system that is composed of a reference diode laser and two tapered amplifiers to control and probe the internal states of atoms, as well as provide the trapping force. I also explore the optical molasses and chirped cooling techniques which help load the atoms into a magneto-optical trap. The successful demonstration of this method of creating a cold atom source leads us to believe that the magnetically decelerated supersonic atoms will play an important role in the area of cold atom physics