Precision test of statistical dynamics with state-to-state ultracold chemistry

Abstract

Chemical reactions represent a class of quantum problems that challenge both the current theoretical understanding and computational capabilities. Reactions that occur at ultralow temperatures provide an ideal testing ground for quantum chemistry and scattering theories, as they can be experimentally studied with unprecedented control, yet display dynamics that are highly complex. Here, we report the full product state distribution for the reaction 2KRb → K 2 + Rb 2 . Ultracold preparation of the reactants grants complete control over their initial quantum degrees of freedom, while state-resolved, coincident detection of both products enables the measurement of scattering probabilities into all 57 allowed rotational state-pairs. Our results show an overall agreement with a state-counting model based on statistical theory, but also reveal several deviating state-pairs. In particular, we observe a strong suppression of population in the state-pair closest to the exoergicity limit, which we precisely determine to be 9.7711 +0.0007 −0.0005 cm −1 , as a result of the long-range potential inhibiting the escape of products. The completeness of our measurements provides a valuable benchmark for quantum dynamics calculations beyond the current state-of-the-art.

Near-threshold scaling of resonant inelastic collisions at ultralow temperatures

“…More generally, it suggests that it is the energetics of a collisional EE process (resonant vs. exothermic) rather than the change in the internal states of collision partners, that determines the process' threshold behavior. Our results demonstrate a universal T ∆m12+1/2 suppression of a wide class of resonant EE processes at ultralow temperatures, which could be observed experimentally for, e.g., spin-exchange atomatom collisions in optical tweezers [49], atom-ion collisions in an optical lattice setup, which allows for high collision energy resolution [68], as well as in cold and ultracold collisions of Yb atoms [69], Ti atoms [70], Ry-dberg atoms [28,29] and polar molecules [7,11].…”

“…Introduction. The unique controllability of ultracold atomic and molecular collisions [1][2][3][4][5][6][7][8][9][10] gives rise to numerous applications of ultracold quantum gases in quantum information science and on precision tests of foundations of chemical and statistical physics [5,11]. Further, much progress has been achieved over the last few years in our ability to observe the reactants and products of molecular collisions and chemical reactions in single, well-controlled quantum states [6][7][8][9]11].…”

“…The unique controllability of ultracold atomic and molecular collisions [1][2][3][4][5][6][7][8][9][10] gives rise to numerous applications of ultracold quantum gases in quantum information science and on precision tests of foundations of chemical and statistical physics [5,11]. Further, much progress has been achieved over the last few years in our ability to observe the reactants and products of molecular collisions and chemical reactions in single, well-controlled quantum states [6][7][8][9]11]. Recent examples include precision studies of photoexcited reaction complexes [9] and product state distributions [11] in the ultracold chemical reaction KRb + KRb → K 2 + Rb 2 , electric field-induced dipolar exchange resonances in KRb + KRb collisions [7], and microwave shielding of NaK + NaK collisions [8].…”

“…Further, much progress has been achieved over the last few years in our ability to observe the reactants and products of molecular collisions and chemical reactions in single, well-controlled quantum states [6][7][8][9]11]. Recent examples include precision studies of photoexcited reaction complexes [9] and product state distributions [11] in the ultracold chemical reaction KRb + KRb → K 2 + Rb 2 , electric field-induced dipolar exchange resonances in KRb + KRb collisions [7], and microwave shielding of NaK + NaK collisions [8]. In addition, observations have been made of ultracold atom-molecule collisions in an optically trapped Na -NaLi( 3 Σ) mixture, of CaF( 2 Σ) + CaF( 2 Σ) collisions in an optical dipole trap [12] and of cold O 2 ( 3 Σ) + O 2 ( 3 Σ) collisions in a magnetically trapped gas of oxygen molecules [13].…”