Stimulated decay and formation of antihydrogen atoms

Abstract

Antihydrogen atoms are routinely formed at the Antiproton Decelerator at CERN in a wide range of Rydberg states. To perform precision measurements, experiments rely on ground state antimatter atoms which are currently obtained only after spontaneous decay. In order to enhance the number of atoms in ground state, we propose and assess the efficiency of different methods to stimulate their decay. At first, we investigate the use of THz radiation to simultaneously couple all n-manifolds down to a low lying one with sufficiently fast spontaneous emission toward ground state. We further study a deexcitation scheme relying on state-mixing via microwave and/or THz light and a coupled (visible) deexcitation laser. We obtain close to unity ground state fractions within a few tens of µs for a population initiated in the n = 30 manifold. Finally, we study how the production of antihydrogen atoms via stimulated radiative recombination can favourably change the initial distribution of states and improve the overall number of ground-state atoms when combined with the stimulated deexcitation proposed.

Induced THz transitions in Rydberg caesium atoms for application in antihydrogen experiments

“…Relying on a pulsed CE production scheme the initially populated states can be mixed by applying an additional electric field to the already present magnetic one [16]. A deexcitation/mixing scheme based on the stimulation of atomic transitions via light in the THz frequency range is thoroughly discussed in [14] for the 3BR case. This latter scheme is equally applicable to a pulsed CE production.…”

“…In a previous publication [14] the stimulation of atomic transitions in (anti-)hydrogen using appropriate light in order to couple the initial population to fast spontaneously decaying levels was studied. Indeed, such techniques allow to increase the ground state fraction within a few microseconds which corresponds to an average flight path of the atoms on the order of centimeters.…”

“…Different deexcitation schemes, making use of THz light, microwaves and visible lasers were investigated. Microwave sources and lasers at the wavelengths and intensities identified in [14] are commercially available and measurements of single Rydberg-Rydberg transitions have been reported [15]. The simultaneous generation of multiple powerful light frequencies in the high GHz to THz regime however still remains a technical challenge.…”

Measurement of the principal quantum number distribution in a beam of antihydrogen atoms

“…The observed production rate of atoms in the lowest lying states (n threshold = 15 and n 100% = 19) which are most interesting for ground state hyperfine spectroscopy, amounts to 0.395 ± 0.096 per run with an observed significance of 6.8 σ. The average spontaneous decay time to ground state from the n = 19 state assuming equi-population of its sub-states is ∼ 130µs [73]. Assuming an average velocity of approximately 1000 m/s (temperature of 50 K)-which is the acceptance limit of our spectroscopy apparatus-the antiatoms are likely to decay to the ground state before entering the microwave cavity (except for antiatoms decaying to the metastable 2s state), which will be installed at the current position of the detector (i.e.…”

“…Hence current efforts focus on investigating methods to boost the production rate, e.g. by decreasing the positron temperature [46] and also pursuing deexcitation techniques like collisional deexcitation in plasmas [77] and light-stimulated deexcitation [73] to increase the number of H atoms in the ground state that reach the cavity.…”