Photodissociation of Trapped Rb2+ : Implications for Simultaneous Trapping of Atoms and Molecular Ions

Abstract

The direct photodissociation of trapped 85 Rb + 2 (rubidium) molecular ions by the cooling light for the 85 Rb magneto-optical trap (MOT) is studied, both experimentally and theoretically. Vibrationally excited Rb + 2 ions are created by photoionization of Rb 2 molecules formed photoassociatively in the Rb MOT and are trapped in a modified spherical Paul trap. The decay rate of the trapped Rb + 2 ion signal in the presence of the MOT cooling light is measured and agreement with our calculated rates for molecular ion photodissociation is observed. The photodissociation mechanism due to the MOT light is expected to be active and therefore universal for all homonuclear diatomic alkali metal molecular ions.PACS numbers: Keywords:The spatially overlapped trapping of cold atoms and ions [1][2][3][4][5][6][7] has significantly expanded our ability to study interactions in cold, dilute gas ensembles. In particular, atomic ion-atom collisions, charge exchange collisions [6-10], sympathetic cooling of ions by ultracold trapped atoms [5,[10][11][12][13], three body reactions [14][15][16] and molecular ion formation processes [3,17] have been investigated. Two complementary directions motivate key goals for future work, (a) the low partial wave ionatom collisions which explores quantum scattering and many particle physics and (b), the controlled collisions between the cold molecular ions produced in the ionatom traps with co-trapped neutral atoms [18] and with light.A critical question which arises is whether the molecular ions can be trapped for a substantial extent of time simultaneously with an ensemble of cold atoms in order to study the interaction between them. In this letter, we address the possibility of simultaneous trapping of 85 Rb + 2 molecular ions with ultracold 85 Rb atoms in a magneto-optical trap (MOT). Our experimental observation shows that the cooling light for the Rb MOT leads to rapid destruction of the measured Rb + 2 ion signal. We measure the lifetime of trapped Rb + 2 in the presence of 780.2413 nm (≡ 12816.54 cm −1 ) light to be 495±80 ms. We discuss possible dissociation mechanisms and show that the experimental observation is in agreement with our theoretical calculations for the photodissociation of Rb + 2 molecular ions.The observed photodissociation mechanism is expected to be universal to all diatomic homonuclear alkali molecular ions as they exhibit similar potential energy characteristics.The experimental system consists of an ion-atom hybrid trap assembly as shown in Fig. 1. The detailed description of the experimental system can be found in ear- lier work [5,19,20]. Briefly, the hybrid trap consists of a MOT for atoms and a modified spherical Paul trap made of four tungsten wire loops in a square shape geometry for trapping ions. The ion trap radio frequency (rf) of 500 kHz with 150 V amplitude is applied to the inner pair of wires and a small (-5 V) constant potential is applied on the outer wires. The ion trap is operated at the optimal trapping voltage for Rb + 2 ions. For the expe...

Cold hybrid ion-atom systems

“…where the expressions in round brackets are 3j symbols, 2S+1 L||Q 2(4) || 2S+1 L is the reduced matrix element of the quadrupole (hexadecapole) moment, and α 0 (iω) and α 2 (iω) are the scalar and tensor components of the dynamic electric dipole polarizability at imaginary frequency of the atom in the 2S+1 L state. The electronic structure data, including the potential energy curves for the ground and excited electronic states, transition electric dipole moments, and matrix elements of the spin-orbit coupling have been calculated for several ion-atom systems relevant for ongoing experimental efforts: (Na+Ca) + (Gacesa et al, 2016;Makarov et al, 2003), (Rb+Ba) + (Knecht et al, 2010;Krych et al, 2011), (Li/Na/K/Rb/Cs+Sr) + , (Rb+Ca) + (Belyaev et al, 2012;Tacconi et al, 2011), (Rb+Yb) + (Lamb et al, 2012;McLaughlin et al, 2014;Sayfutyarova et al, 2013), (Li+Yb) + da Silva Jr et al, 2015;Tomza et al, 2015), (Ca/Sr/Ba/Yb+Cr) + (Tomza, 2015), (Li+Be) + (Ghanmi et al, 2017), (Li+Mg) + (ElOualhazi and , (Li+Ca) + (Saito et al, 2017), (Li+Sr) + (Jellali et al, 2016), (Rb+Ca/Sr/Ba/Yb) + (da Silva Jr et al, 2015), (Na/Ka/Rb+Be) + (Ladjimi et al, 2018), (Li+Li) + (Bouchelaghem and Bouledroua, 2014;Bouzouita et al, 2006;Musia l et al, 2015), (Na+Na) + (Berriche, 2013;Bewicz et al, 2017), (K+K) + (Skupin et al, 2017), (Rb+Rb) + (Jraij et al, 2003;Jyothi et al, 2016), (Cs+Cs) + (Jamieson et al, 2009;Jraij et al, 2005), (Li+Na) + (Li et al, 2015;Musia l et al, 2018), (Li+K) + (Berriche et al, 2005;…”

Cold chemistry: a few-body perspective on impurity physics of a single ion in an ultracold bath

“…This complex cold reaction network is experimentally corroborated by looking at the relevance of different ionic species as a function of time [80]. Finally, we would like to point out that the role of external laser sources on few-body processes has also been observed in molecular ion-atom systems [11,95].…”

Vibrational Quenching of Weakly Bound Cold Molecular Ions Immersed in Their Parent Gas

“…The first step needed to derive the potential matrix (3) is to calculate the twobody rovibrational wavefunctions of the molecular ion alone and their binding energies. State of the art ab initio methods can be used to calculate the interaction potential of Rb + 2 in the electronic ground state with a finite precision of the order of 1% [32]. While this kind of accuracy is sufficient for spectroscopic data such as the vibrational spacing of the lower levels, it is unfortunately not enough to predict the binding energies of the weakly bound Rb + 2 states.…”