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.
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.
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.
Abstract Efficient cooling of trapped charged particles is essential in many fundamental physics experiments, for high-precision metrology, and for quantum technology. Until now, ion-ion coupling for sympathetic cooling or quantum state control has been limited to ion species with accessible optical transitions or has required close-range Coulomb interactions. To overcome this limitation and further develop scalable quantum control techniques, there has been a sustained desire to extend laser-cooling techniques to particles in macroscopically separated traps, opening quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions, and antimatter particles. Here, we demonstrate sympathetic cooling of a single proton by laser cooled Be+ ions stored in a spatially separated Penning trap. The two traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We simultaneously demonstrate the cooling of a resonant mode of a macroscopic LC circuit with laser-cooled ions and sympathetic cooling of an individually trapped proton, reaching temperatures far below the environment temperature. Importantly, as this technique does not rely on the direct Coulomb interaction but rather on image-current interactions, it can be easily applied to an experiment with antiprotons, facilitating improved precision in matter-antimatter comparisons and dark matter searches.
Abstract Cooling and detection schemes using laser cooling and methods of quantum logic can contribute to high precision CPT symmetry tests in the baryonic sector. This work introduces an experiment to sympathetically cool protons and antiprotons using the Coulomb interaction with a ion trapped in a nearby but separate potential well. We have designed and set up an apparatus to show such coupling between two identical ions for the first time in a Penning trap. In this paper, we present evidence for successful loading and Doppler cooling of clouds and single ions. Our coupling scheme has applications in a range of high-precision measurements in Penning traps and has the potential to substantially improve motional control in these experiments.
Efficient cooling of trapped charged particles is essential to many fundamental physics experiments1,2, to high-precision metrology3,4 and to quantum technology5,6. Until now, sympathetic cooling has required close-range Coulomb interactions7,8, but there has been a sustained desire to bring laser-cooling techniques to particles in macroscopically separated traps5,9,10, extending quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions and antimatter. Here we demonstrate sympathetic cooling of a single proton using laser-cooled Be+ ions in spatially separated Penning traps. The traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We also demonstrate the cooling of a resonant mode of a macroscopic LC circuit with laser-cooled ions and sympathetic cooling of an individually trapped proton, reaching temperatures far below the environmental temperature. Notably, as this technique uses only image–current interactions, it can be easily applied to an experiment with antiprotons1, facilitating improved precision in matter–antimatter comparisons11 and dark matter searches12,13.
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.
This thesis is the realization of the long standing goal of sympathetically cooling single particles with image currents. Particles with no electronic structure such as the bare proton or antiproton, are not amenable to standard laser cooling and ma-nipulation techniques and until now have been cooled only by coupling to cryogenictank circuits. In measurements of the proton and antiprotong-factor however, theenergy splitting used to read out the particle’s spin state is larger than thermal en-ergy fluctuations and special techniques are required to perform the measurement.The technique developed here uses a cloud of laser cooled beryllium ions to sym-pathetically cool a single proton by coupling to, and cooling a mode of the tank circuit. The use of this circuit resonantly enhances the energy exchange between the trapped particles and allows the cooling ions to be separated from the particle of interest over arbitrary distances. This technique, is the first demonstration of sympathetic cooling of a proton and a macroscopic LC circuit to below 25% of the environment temperature.Sympathetically cooled protons and antiprotons with this method enable an improved g-factor measurement by increasing the duty cycle of the experiment. This will further our understanding of matter-antimatter asymmetry by constraining CPT odd new physics and enhancing sensitivity to even more exotic physics. More-over, the technique presented here has general applications in experiments with trapped charged particles, enabling coupling of a large number of ions, distributed in many separated trapping regions to a single cold resonator.