Following Marx et al. [Phys. Rev. Lett. 111, 243007 (2013)], we discuss the measurement and manipulation of the temperature of cold CO molecules in a microchip environment. In particular, we present a model to explain the observed and calculated velocity distributions. We also show that a translational temperature can be extracted directly from the measurements. Finally, we discuss the conditions needed for an effective adiabatic cooling of the molecular ensemble trapped on the microchip.
Following Marx et al. [Phys. Rev. Lett. 111, 243007 (2013)], we discuss the measurement and manipulation of the temperature of cold CO molecules in a microchip environment. In particular, we present a model to explain the observed and calculated velocity distributions. We also show that a translational temperature can be extracted directly from the measurements. Finally, we discuss the conditions needed for an effective adiabatic cooling of the molecular ensemble trapped on the microchip.
The subject of this thesis’s work is research of cold molecules on a microchip. On the one hand, cold and ultracold molecules might allow high- precision measurements of molecular properties and the determination of their behavior at the quantum level. On the other hand, one could try to study highly controlled chemical reactions or to build a quantum computer with their help. In the experiments presented here, electrically neutral, polar molecules in low-field-seeking states are trapped and decelerated on a microchip with the help of electric fields. This exploits the Stark effect: the energy level shift of atoms and molecules in an electric field. After manipulation on the chip the molecules can be detected quantum-state specifically via the REMPI method. At first, CO molecules were prepared in the upper Λ-doublet component of the a3Π1, v = 0, J = 1 state, trapped on the chip and get vibrationally excited by an infrared laser in the middle of the chip to the J = 1 or J = 2 rotational state of the vibrational state v = 1. This could be shown experimentally and was analyzed theoretically for molecules which were trapped at all times. Secondly, CO molecules were detected on the chip and the structure of previously trapped molecule clouds of several of the only 120 μm spaced traps was spatially resolved. For this purpose the chip was extended with an ion lens setup, which enabled the determination of the temperature of the clouds by following the free ballistic expansion of the molecules in time; either by comparing the data to trajectory simulations (T = 11 ± 1 mK) or by applying a ballistic expansion model (T = 13 ± 3.5 mK), comparable to the method used by the ultracold atom community. The spatial imaging enabled the observation of a phasespace manipulation scheme, which adiabatically expanded the molecules in the trap and significantly reduces their temperature to approximately one third of their initial value. The third goal was to trap ground state ammonia molecules, which should extend the trapping time and would show that also other molecules could be trapped on the chip. The ammonia isotopologues 14NH3, 14ND3, and 15ND3 in the |vInv = 1, J = 1,K = 1> state of the electronic ground state X were used. No signal could be measured from trapped molecules, which is attributed to large nonadiabatic transitions to untrappable quantum states, leading to severe trap loss. At last, a new chip- based Stark decelerator is presented, which is a miniaturized version of the so-called “traveling-wave” ring decelerator. This chip-based decelerator should be able to trap more molecules compared to the chip that was used so far, and due to improved electronics it should be able to decelerate molecules from molecular beam velocities of approximately 360 m/s down to a standstill, in contrast to large-scale traveling-wave decelerators so far. The chip is still in development to achieve operation with the full specification (voltage). Performance simulations show the usefulness of this design, which needs to be tested in experiments.
We present the integrated imaging of cold molecules in a microchip environment. The on-chip detection is based on resonance-enhanced multiphoton ionization, which is quantum state selective and generally applicable. We demonstrate and characterize time-resolved spatial imaging and subsequently use it to analyze the effect of a phase-space manipulation sequence aimed at compressing the velocity distribution of a molecular ensemble with a view to future high-resolution spectroscopic studies. The realization of such on-chip measurements adds the final fundamental component to the molecule chip, offering a new and promising route for investigating cold molecules.
Abstract Brrrr! Cold molecule and cold atom research are juxtaposed and the challenges in cooling and trapping molecules are recounted. Both indirect and direct techniques of producing cold and slow molecules (such as buffer‐gas cooling and magnetic trapping, see picture) are described. Advanced techniques of manipulating cold or slow molecules are reviewed and ongoing work with cold molecules is outlined. magnified image Herein, we aim to show why the work on translationally (and otherwise) cold molecules has sparked so much inspiration—and anticipation—in both the physics and chemistry communities. We begin by discussing the basic features of cold molecules as implied by their de Broglie wavelengths, large compared with molecular dimensions. We juxtapose cold molecule and cold atom research and recount the challenges that had to be met if molecules were to be cooled and trapped. Subsequently, both the indirect and direct techniques of producing cold and slow molecules are described in some detail, and their applicability to various classes of molecules is discussed. Advanced techniques of manipulating cold or slow molecules are illustrated by the examples of DC and AC trapping and storage. Finally, ongoing and future work with cold and/or trapped molecules is outlined. This includes precision spectroscopy, chemical reaction dynamics, simulations of few‐ and many‐body physics, quantum computing, and tests of fundamental physics.
Sympathetic cooling and Coulomb crystallisation of molecular ions above the \nsurface of an ion-trap chip were demonstrated. N2+ and CaH+ ions were confined \nin a surface-electrode radiofrequency ion trap and cooled by the interaction \nwith laser-cooled Ca+ ions to secular translational temperatures in the \nmilliKelvin range. The configuration of trapping potentials generated by the surface \nelectrodes enabled the formation of planar bicomponent Coulomb crystals \nand the spatial separation of the molecular from the atomic ions. The structural \nand thermal properties of the crystals were characterized using molecular \ndynamics simulations. The effects of trap anharmoncities on the shape and \nenergy of bicomponent crystals were theoretically investigated. It was shown \nthat the trapping potentials can also deliberately be engineered to spatially \nseparate ion species in bicomponent crystals. Furthermore, a multi-functional \nsurface-electrode radiofrequency ion-trap chip has been developed to enable experiments \nwith cold molecular ions using a monolithic device. The chip was \ndesigned to combine various tasks such as loading and preparation of ions, mass \nspectrometry, spectroscopy, reaction studies, and manipulation of ion crystals \nin a miniaturised device. This chip features carefully engineered ion channel \nintersections that enable transporting sympathetically cooled molecular ions in \nthe form of bicomponent crystals. A detailed description of the fabrication and \nsimulation of the two chips are presented. The present study extends chipbased \ntrapping techniques to Coulomb-crystallised molecular ions with potential \napplications in mass spectrometry, cold chemistry, quantum technology, and \nspectroscopy.
In the last years, it was demonstrated that neutral molecules can be loaded on a microchip directly from a supersonic beam. The molecules are confined in microscopic traps that can be moved smoothly over the surface of the chip. Once the molecules are trapped, they can be decelerated to a standstill, for instance, or pumped into selected quantum states by laser light or microwaves. Molecules are detected on the chip by time-resolved spatial imaging, which allows for the study of the distribution in the phase space of the molecular ensemble.
Optics
The temperature of an everyday macroscopic object is well understood and easy to measure. The concept of temperature, however, becomes blurry when the number of particles in a system becomes so small that the ensemble breaks down into a number of individual components, such as for atoms or molecules trapped in an optical lattice and cooled to ultralow temperatures. McDonald et al. demonstrate a spectroscopic technique that uses the line shift and change in the line shape of an atomic or molecular transition to determine the temperature of trapped atoms or molecules down to nanokelvin temperatures. This technique should prove useful in a range of applications, including metrology and probing the energetic dynamics of ultracold chemical reactions.
Phys. Rev. Lett. 114 , 23001 (2015).