Lifetimes of ultralong-range strontium Rydberg molecules in a dense Bose-Einstein condensate

Abstract

The lifetimes and decay channels of ultralong-range Rydberg molecules created in a dense BEC are examined by monitoring the time evolution of the Rydberg population using field ionization. Studies of molecules with values of principal quantum number, n, in the range n = 49 to n = 72 that contain tens to hundreds of ground state atoms within the Rydberg electron orbit show that their presence leads to marked changes in the field ionization characteristics. The Rydberg molecules have lifetimes of ∼ 1 − 5 µs, their destruction being attributed to two main processes: formation of Sr + 2 ions through associative ionization, and dissociation induced through L-changing collisions. The observed loss rates are consistent with a reaction model that emphasizes the interaction between the Rydberg core ion and its nearest neighbor ground-state atom. The measured lifetimes place strict limits on the time scales over which studies involving Rydberg species in cold, dense atomic gases can be undertaken and limit the coherence times for such measurements.

Loss rates for high-$n$, $49\lesssim n \lesssim150$, 5sns($^{3}$S$_{1}$) Rydberg atoms excited in an $^{84}$Sr Bose-Einstein condensate

“…Following excitation the number and excited-state distribution of the surviving Rydberg atoms is measured as a function of the delay time, t D , from the end of the laser pulse using selective field ionization (SFI) [15,26,27] for which purpose the atoms are subject to a time-dependent electric field of the form E(t) = E p (1−e −t/τ ) with a time constant τ ∼ 6µs. Ionization, however, typically begins ∼ 1µs from the start of the field ramp.…”

“…Measurements have since been extended to include a variety of different atomic species and atomic states [4][5][6][7][8], and have demonstrated the formation of molecules containing multiple bound groundstate atoms, i.e., trimers, tetramers, ... [9][10][11]. More recently, studies of "molecule" formation and loss in Bose-Einstein condensates (BECs) have been reported where the very-high ground-state atom densities (approaching 10 15 atoms cm −3 ) allow the production of Rydberg atoms whose electron orbits can enclose hundreds or even thousands of ground-state atoms [12][13][14][15]. This work has demonstrated that such species provide an opportunity to probe the properties of cold dense gases [16,17], to image the electron wavefunction [18,19], and to examine many-body phenomena such as the creation of Rydberg polarons in quantum degenerate gases [20].…”

“…The reactions responsible for atomic loss, which involve a collision between the Rydberg core ion and nearestneighbor ground-state atom, were investigated and identified. More recently the lifetimes of strontium 5sns( 3 S 1 ) Rydberg atoms with n = 49 − 72 produced in an 84 Sr BEC have been explored [14,15]. Again lifetimes of ∼ 1 − 10µs were observed.…”

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

“…However, it was observed that the Rydberg lifetime is much shorter when placed in a bath than in vacuum. This was a mystery until it was realised that the faster decay rate is a consequence of an inelastic few-body process and a reactive one [69,70]. The inelastic process is known as l-changing collision [71], in which the Rydberg state ends up in a high angular momentum state after colliding with a neutral atom.…”

Dynamics of atoms within atoms

“…The study of quantum impurities has become an important branch of ultra-cold atomic physics, allowing explorations of condensed matter phenomena ranging from the Kondo effect [1,2] over polaron formation [3,4,5,6,7] to the Anderson orthogonality catastrophe [8]. A unique impurity object in this context is a Rydberg atom in a Bose-Einstein Condensate (BEC) [9,10,11,12,13,14]. Due to the extreme radius of the Rydberg electron density distribution r orb ≈ 2a 0 n 2 , which can reach r orb ≈ 1.8µm at n = 133, one can enter the realm where tens of thousands of ground-state atoms are located inside the Rydberg orbit and can be set into motion by collisions with the Rydberg electron during the life-time of the latter.…”