Alphatrap is a Penning-trap experiment aiming for the test of bound-state quantum electrodynamics (QED) by measuring the g-factor of electrons bound in highly charged ions up to hydrogen-like 208Pb81+. The high atomic number Z allows a test of boundstate QED under highest field strengths. Cold ions are necessary for high-precision measurements revealing the small additional effect of QED. As a novel development, laser cooling of beryllium ions will be used to sympathetically cool highly charged ions. The lower achievable temperatures are expected to further increase the precision of the measurement. Additionally, new measurement schemes such as simultaneous g-factor measurements on Coulomb crystallized ion pairs become feasible. In the context of this thesis, a concept for implementation of laser cooling at the Alphatrap experiment using 313nm light was developed. The experiment specific requirements on laser cooling in a Penning trap and sympathetic cooling are discussed and the results of the commissioning of the laser system are presented.
Alphatrap is a Penning-trap experiment aiming for the test of bound-state quantum electrodynamics (QED) by measuring the g-factor of electrons bound in highly charged ions up to hydrogen-like 208Pb81+. The high atomic number Z allows a test of boundstate QED under highest field strengths. Cold ions are necessary for high-precision measurements revealing the small additional effect of QED. As a novel development, laser cooling of beryllium ions will be used to sympathetically cool highly charged ions. The lower achievable temperatures are expected to further increase the precision of the measurement. Additionally, new measurement schemes such as simultaneous g-factor measurements on Coulomb crystallized ion pairs become feasible. In the context of this thesis, a concept for implementation of laser cooling at the Alphatrap experiment using 313nm light was developed. The experiment specific requirements on laser cooling in a Penning trap and sympathetic cooling are discussed and the results of the commissioning of the laser system are presented.
The Penning trap experiment Alphatrap tests quantum electrodynamics via g- factor measurements of bound electrons in highly charged ions (HCI). The precision of the measurements can be improved by cooling the HCI. This thesis describes a novel and versatile method to sympathetically cool HCIs with laser-cooled beryllium ions efficiently in high-precision Penning traps. The method is based on increasing the coupling of two ions stored in separate penning traps by adding an electrical tank circuit. In a proof of principle measurement this was demonstrated using a 84Kr23+ and 40Ar11+ ion: first, we saw an avoided crossing of the ion modes, and second, we showed a Rabi oscillation in the energy transfer. Our coupling technique enables active control of the coupling strength between the ions, so that a coupling time of τ = 0:856(16) s was achieved. We see this as a possible tool to efficiently cool a wide range of ion species. In addition, an active beam stabilization system was installed to reduce fluctuations of the cooling laser beam position and orientation, and to improve the alignment of the laser with respect to the beryllium ions. This system was calibrated and geometric losses of the laser transmission through our Penning trap setup were estimated.
One of the best ways to study antimatter is to investigate antihydrogen, the bound state of an antiproton and a positron. Antihydrogen atoms do not exist naturally and must be synthesized in the lab by merging carefully-prepared plasmas of positrons and antiprotons. If the atoms are created in a magnetic trap like the one used by the ALPHA experiment at CERN, then a fraction of the coldest atoms remain trapped, while the rest escape and annihilate on the trap walls. The trapped atoms may then be probed using microwaves or lasers to make high-precision comparisons with hydrogen. Increasing the trapping rate would allow us to perform precision measurements on antihydrogen in a shorter period of time and with better systematics. Particle simulations indicate that by sympathetically cooling positrons using laser-cooled beryllium ions, we have the ability to improve the antihydrogen trapping rate by up to two orders of magnitude. This thesis describes the effort to design and qualify a beryllium ion source that is compatible with the extreme environment of the ALPHA trapping apparatus. To produce the ions, pulsed laser ablation of a beryllium target is investigated and the ion plume is characterized. By carefully choosing the laser parameters, a plume with a suitable number of ions and kinetic energy distribution can be created for subsequent trapping and laser-cooling in a Penning trap. This thesis reports the successful demonstration of the ion source, in particular its compatibility with the requirements of the ALPHA experiment. The ion source has been installed into the main apparatus at ALPHA and is expected to be commissioned early next year.
High precision comparisons of the proton and antiproton g-factor enable stringent tests of CPT symmetry in the baryonic sector. However, current measurement routines suffer from long preparation times and high particle temperatures, which complicate the increase of the precision beyond the parts per billion regime. As a solution, new sympathetic cooling schemes based on co-trapped laser-cooled ions may be used to cool (anti-)protons to the ground state of motion and to significantly decrease particle preparation times. In addition, motional coupling to an auxiliary ion in a double-well potential can be used for the implementation of new readout schemes based on quantum logic spectroscopy for the spin-state of the (anti-)protons. This thesis describes a cryogenic Penning trap system for ground state cooling of single 9Be+ ions, which represents the latest development of the BASE experiment in Hannover towards the implementation of sympathetic cooling schemes and quantum logic spectroscopy of single (anti-)protons. Furthermore, the setup and implementation of lasers systems at 313nm for Doppler cooling, repumping and Raman interactions are described. To this end, an optical platform for laser beam delivery to the vacuum system and an optical phase-locked loop for the stabilization of the relative phase of two lasers at 313 nm are presented. In this work, the laser systems are used for measurements of the optical resonance frequencies for cooling, probing and repumping of 9Be+ ions. In addition, stimulated Raman transitions are demonstrated using two phase-locked lasers at 313nm. In the following, this technique is used for high-precision measurements of the qubit frequency and the magnetic field, as well as themometry measurements with 9Be+ ions. The temperature of the ions after Doppler cooling is measured as a function of the cooling laser parameters and a minimal axial mode temperature of 1.77(10) mK is obtained. The results of this thesis pave the way for sideband spectroscopy and ground state cooling of single 9Be+ ions in Penning traps, which is an essential prerequisite for sympathetic ground state cooling of single (anti-)protons and the application of quantum logic spectroscopy to (anti-)proton g-factor measurements in the future.
ALPHATRAP is a Penning-trap based experiment located at the Max-Planck-Institut für Kernphysik (MPIK). It is dedicated to the exploration of ground-state properties of heavy, highly charged ions (HCI). The major goal of the ALPHATRAP \nexperiment are high precision measurements of the bound-electron g-factor. The comparison of the experimental result with recent theoretical calculations will not only serve as a sensitive test of bound-state quantum electrodynamics (BS-QED) but also yields a new approach for the determination of fundamental constants such as the electron mass or the fine structure constant. The measurement of the bound-electron g-factor of a single HCI is performed in an optimized cryogenic double Penning-trap setup, utilizing the continuous Stern-Gerlach effect. For injection of externally produced HCI up to 208Pb81+ the ALPHATRAP experiment is \ncoupled to various ion sources, including the Heidelberg Electron-Beam Ion Trap. \nThis thesis describes the setup and preparation of the ALPHATRAP experiment on its way towards its first g-factor measurement. In this context a new highly sensitive detection system was implemented and successfully tested. This enabled a first commissioning of the whole apparatus with in situ generated HCI as well as HCI injected through the room temperature beamline. The first-time integration \nof an externally operable cryogenic valve allowed for excellent vacuum conditions with long ion storage times. The implementation of typical ion detection and manipulation techniques was demonstrated by characterization measurements of the detection system and the trapping fields. The commissioning culminated in the first direct observation of induced bound-electron spin transitions at the \nALPHATRAP experiment.
The comparison of the g-factors of the proton and the antiproton is a stringent test of CPT invariance. The state-of-the-art method for the determination of the (anti-)proton's g-factor is the application of the continuous Stern-Gerlach effect. With this method, precisions in the low parts per billion regime could be achieved. However, preparation times for cold enough particles are on the order of minutes to hours. The implementation of sympathetic cooling using a co-trapped atomic ion could lead to preparation times in the milliseconds regime. Furthermore, the applicability of sympathetic cooling would enable an alternative readout scheme using quantum logic methods. This thesis presents a Penning trap system that is designed for ground state cooling, adiabatic transport, and motional coupling of single 9Be+ ions. It has been built in a modular manner, giving the option of adapting it for motional coupling and sympathetic cooling of single (anti-)protons. In the course of this work, the prerequisites for motional coupling of 9Be+ ions have been fulfilled: A cloud of 9Be+ ions was cooled to a temperature of 1.7~mK applying Doppler cooling. The achieved temperature is about three times the Doppler limit which is 0.5~mK for beryllium ions. Furthermore, a scheme for reproducible loading of the trap and reducing the particle number was developed. Finally, first transport in our apparatus was demonstrated with clouds of beryllium ions. The method used for that is directly applicable to single ions. The results of this work pave the way towards adiabatic transport of single 9Be+ ions, which is crucial for sympathetic cooling of (anti-)protons in a double-well potential as well as for implementing quantum logic spectroscopy with single (anti-)protons.
The objective of the project is to perform high-resolution Doppler-free two-photon vibrational spectroscopy of the H2+ molecular ion for accurate electron to proton mass ratio determination. Trapping and laser-cooling of the H2+ ions is necessary. Since H2+ molecular ions cannot be directly laser cooled, a solution is the implementation of sympathetic cooling via a laser cooled Be+ ions. In the first part of this thesis the design and implementation of a linear Paul trap is presented. This trap is suitable to confine H2+ and Be+ ions while allowing good optical access for multiple laser sources and the imaging system. The second part describes a low power, diode based laser system to provide narrow linewidth 626nm light, and a high power, fiber laser based laser system. Subsequently, a bow-tie cavity is presented to frequency double the 626nm light to obtain 313nm light for Be+ Doppler-cooling. In the last part the operational readiness of the trap and the fiber laser based 313nm laser source is demonstrated by the observation of Be+ Coulomb crystals. Electron impact ionization of H2 present in the residual gas allows to observe sympathetic cooling and shows that the developed setup can provide the experimental conditions for precision spectroscopy of H2+.