title: Controlled manipulation of atoms in Rydberg quantum states for application in experiments with antihydrogen
Creators: name: Wolz, Tim
Publisher: name: UNSPECIFIED
Year: 2022

description: Antihydrogen atoms are synthesized via charge-exchange or three-body-recombination processes for stringent CPT symmetry and gravity tests on antimatter at CERN's Antiproton Decelerator. While the atoms are produced in a wide range of highly excited Rydberg states, experiments rely on ground state antihydrogen which are currently obtained only via spontaneous emission. Due to radiative lifetimes of the order of milliseconds, the decay toward ground state is slow. Magnetic neutral-atom traps allow to hold onto the initially formed antihydrogen. Here, ground state atoms are obtained via spontaneous decay along the trapping potential and spectroscopy measurements can be performed inside the trap. Typical traps capture maximum temperatures (for ground state atoms) of roughly 500mK. State-of-the-art formation temperatures, however, lie around 40K. Due to the large difference between formation and trappable temperature, currently best achieved trapping fractions of antihydrogen amount to only 0.01%. As an alternative, the formed anti-atoms can be extracted out of their formation region into a beam allowing for close to field-free measurements. At the given velocities, the Rydberg radiative decay toward ground state is too slow to establish a significant population of the ground state through spontaneous emission even within a few meter long beam path. In addition, an efficient beam formation would require antihydrogen in ground state close to the formation region. This work thus deals with the controlled manipulation of Rydberg atoms to stimulate their decay toward ground state. In order to address the initial distribution of Rydberg levels with deexcitation lasers, state-mixing can be achieved through pulsed electric fields that are added to the already present magnetic one in state-of-the-art formation traps. Another possibility lies in mixing the states with light in the THz and microwave frequency range. In both cases, visible lasers allow to very efficiently transfer the mixed population toward the ground state via intermediate strongly bound states that decay on a few nanosecond timescales. In a three-body-recombination reaction the capture of positrons into a bound state of antiprotons can be enhanced relying on stimulated radiative recombination. This approach can be combined with the developed techniques to deexcite bound levels. In trap experiments use-cases of deexcitation for cooling within a magnetic field gradient to enhance the trapping fraction of antihydrogen atoms exist. The second part of the thesis deals with the experimental implementation of the methods theoretically identified in part one. Deexcitation light sources are tested and a hydrogen Rydberg beamline for a proof-of-principle experiment is designed, built and commissioned. Different Rydberg beam production schemes are discussed and experimentally assessed. Rydberg state formation is observed within a microwave discharge plasma and a hydrogen 2s to Rydberg excitation laser is commissioned.