Coherent Atom-Trimer Conversion in a Repulsive Bose-Einstein Condensate

Abstract

We show that the use of a generalized atom-molecule dark state permits the enhanced coherent creation of triatomic molecules in a repulsive atomic Bose-Einstein condensate, with further enhancement being possible in the case of heteronuclear trimers via the constructive interference between two chemical reaction channels.PACS numbers: 03.75. Pp, 03.70.+k The experimental realization of Bose-Einstein condensates (BEC) in dilute atomic vapors has led to a number of spectacular advances with implications well past the confines of traditional atomic, molecular and optical (AMO) physics [1], and with profound relevance for fields ranging from condensed matter physics to quantum information science. A development of particular relevance for the present study is the generation and probing of ultracold molecular samples and of molecular condensates from atomic BEC, using magnetic Feshbach resonances (FR) and photoassociation (PA) [2-6] to control the dynamics of the system. In particular, it has recently been shown that these two techniques can be combined to achieve the efficient and stable conversion of atoms into molecular dimers [3].The goal of this paper is to demonstrate theoretically that these techniques can in principle be extended to the generation of molecular trimers. An important new result is that the creation of heteronuclear trimers can be significantly enhanced by the constructive interference of two quantum channels leading to their formation from a two-component atomic condensate. The basic idea is to first create highly excited dimers via a standard FR, and then to couple them to a bound trimer via PA. A key element of the scheme is to exploit a coherent population trapping (CPT) technique to prevent the dimer population from becoming significant throughout the conversion process. Such a scheme has previously been proposed for the creation of molecular dimers [3], and has been theoretically demonstrated to be stable for a broad range of conditions. This proposed extension of "superchemistry" [6] manipulations from dimers to trimers exploits the existence of three-body bound states in ultracold atomic samples as the scattering length for two-body collisions becomes infinite. As discussed in Ref. [7] this occurs not only for identical particles, a situation first considered by Efimov [8-10], but also for two identical and one different particle. In particular, in the case of two heavy particles and one light particle these authors found that the heavyheavy interaction does not matter, and there is an infinite number of bound trimer states as long as the light-heavy scattering length becomes infinite. In the case of the interaction between one heavy and two light particles, by contrast, there is no infinite number of bound states unless both two-body scattering lengths become simultaneously infinite.We mentioned that a point of particular interest in the formation of heteronuclear trimers A 2 B is the role of quantum interferences between the two paths that involve intermediate dimers A 2 (path AA) a...

Quantum Noise in the Collective Abstraction ReactionA+B2→AB+B

“…From a theoretical point of view, this implies that the mean-field Gross-Pitaevskii equation is not appropriate to describe the early stages of the coherent bimolecular reaction, and can be used only once the product reactant populations become macroscopic. This is in contrast with single-molecular combination reactions such as the atom-dimer [2,6] or atom-trimer conversion [10], and is reminiscent of quantum or atom optics situations such as the laser, superradiance and matter-wave superradiance, see for instance Refs. [11,12,13].…”

“…(2) imply that there is no growth in the populations of the atoms B and of the dimers AB. This indicates that the mean-field GrossPitaevskii equations, which are adequate to describe the short-time behavior of the familiar coherent atom-dimer or atom-trimer conversion [6,10], break down completely in studying the onset of this bimolecular reaction.…”

“…An important feature of the coherent abstraction reaction is that it can be controlled and optimized by exploiting the existence of a CPT dark state [5,10]. Under a dynamical two-photon resonance condition, Eqs.…”

Quantum superchemistry of de Broglie waves: New wonderland at ultracold temperature

“…Reproduced from Ref. [77], Copyright c 2007 The American Physical Society. Figure 6 plots the steady-state trimer number N g,s as a function of η l = λ l /Ω l , l = 1, 2, as well as the parameter…”

“…Nevertheless, superchemistry certainly includes more complex couplings like a+a+a → g [73][74][75][76] or a+a → d, a + d → g [77,79], where a, d, g denote the atom, dimer, and trimer, respectively. In fact, the indirect evidence for three-body or four-body bound states has been observed, such as 6 Li 3 [74], 40 K 3 [75], Cs 3 [16][17][18], 87 Rb 40 K 6 Li [80], and 133 Cs 4 [81].…”