Laser-stimulated deexcitation of Rydberg antihydrogen atoms

Abstract

Antihydrogen atoms are routinely formed at CERN in a broad range of Rydberg states. Groundstate anti-atoms, those useful for precision measurements, are eventually produced through spontaneous decay. However given the long lifetime of Rydberg states the number of ground-state antihydrogen atoms usable is small, in particular for experiments relying on the production of a beam of antihydrogen atoms. Therefore, it is of high interest to efficiently stimulate the decay in order to retain a higher fraction of ground-state atoms for measurements. We propose a method that optimally mixes the high angular momentum states with low ones enabling to stimulate, using a broadband frequency laser, the deexcitation toward low-lying states, which then spontaneously decay to ground-state. We evaluated the method in realistic antihydrogen experimental conditions. For instance, starting with an initial distribution of atoms within the n = 20 − 30 manifolds, as formed through charge exchange mechanism, we show that more than 80% of antihydrogen atoms will be deexcited to the ground-state within 100 ns using a laser producing 2 J at 828 nm. arXiv:1810.06736v2 [physics.atom-ph]

Stimulated decay and formation of antihydrogen atoms

“…A key point is that the characteristic deexcitation time is fundamentally limited by the number of states addressed. This observation led to the correction of a previously published [19] result which was neglecting the repopulation of the initial manifold. A final dissipative spontaneous process is required to drive the population down and should be as fast as possible, hence the choice of low-lying end states, the 2p level being the optimal choice to maximize the overall ground-state population rate (but not necessarily the optimal choice in terms of experimental feasibility).…”

“…This small additional field (typically ∼ 10 V/cm) can lead to a perturbation of the states [26][27][28]. A complete study of the combined magnetic and electric field effects is outside the scope of this paper, but in general it will create an additional mixing [19] which is beneficial to the deexcitation goal, but will also induce potential losses through new excitation channels.…”

“…This is similar to the assumption of a full k (or l) mixing (as done in the appendix §A 5). Formulae for σ κ,l n,l are given in [19]. We implement ionization rates Γ κ n,m = Ī hω σ κ n,m for the entire set of intensities I and frequencies ω used (all the ones driving ∆n = −1 transitions from n = 30 down to low n states).…”

“…In order to correct the results of Ref. [19], we solved the set of rate equations for all mixed (n, m 1 , m 2 ) levels with 20 ≤ n ≤ 30 under the presence of the optimum electric and magnetic field values found in [19] and implement laser stimulated rates to the n = 3 manifold that decays spontaneously to ground state. We found that ∼ 60% of the atoms with an initial statistical distribution in the 20 ≤ n ≤ 30 manifolds are brought to ground state within 10 µs which is in good agreement with the considerations and the generic model presented above.…”

“…Therefore, it is highly necessary that a stimulated deexcitation takes place at the moment of formation to quickly populate the ground-state level. In a previous publication [19] we have dealt with the case of pulsed deexcitation which can only be applied to pulsed CE formation. The proposed mechanism could achieve deexcitation to ground state in a sub-µs timescale, but suffered from a caveat that was overseen by the authors.…”