Dynamics of two atoms undergoing light-assisted collisions in an optical microtrap

Abstract

We study the dynamics of atoms in optical traps when exposed to laser cooling light that induces light-assisted collisions. We experimentally prepare individual atom pairs and observe their evolution. Due to the simplicity of the system (just two atoms in a microtrap) we can directly simulate the pair's dynamics, thereby revealing detailed insight into it. We find that often only one of the collision partners gets expelled, similar to when using blue detuned light for inducing the collisions. This enhances schemes for using light-assisted collisions to prepare individual atoms and affects other applications as well. PACS numbers:Optically trapped cold atoms provide an exciting platform for studying the change in atom-atom interactions due to absorption or emission of light. The advantage of such a system is that the atoms are isolated from their surroundings and basic physical effects in photochemistry can be studied without interference from processes induced by the environment. Recently this has led to controlled formation of ultra-cold molecular gases [1,2] and in the past, photo-association spectroscopy has provided detailed knowledge about atom-atom interaction potentials [3,4].Typically, experiments on photo-association or lightassisted collisions of cold atoms are conducted on large samples. Studying microscopic processes at the individual event level reveals information hidden in ensemble averages of larger samples [5,6]. Pioneering work in studying individual light-assisted collisions was conducted using small samples of atoms in a high gradient MagnetoOptical Trap (MOT) [7,8]. Those studies observed that up to 10% of loss events manifested themselves as just one of the collision partners being lost from the MOT.Of particular interest to many modern experiments in atomic physics are light-assisted collisions or photoassociation events induced by near-resonant light. This phenomenon is of fundamental interest [9] and plays a crucial role in modern laser cooling experiments. In addition, light-assisted collisions have been employed to isolate individual atoms in optical microtraps [10][11][12][13][14], to redistribute atoms loaded into an array of traps [15], and to perform parity number measurement of atoms in optical lattices [16,17]. Isolation experiments that used bluedetuned light to induce collisions have achieved high efficiency, whereas experiments using red detuned light have reported efficiencies of about 50%. For several of these applications it is assumed that both atoms of the pair are lost from the optical microtrap when they undergo light-assisted collisions.Here we revisit the ejection of atoms from a far off resonance optical trap due to light-assisted collisions induced by red-detuned laser cooling light. We implement the idealized collision experiment in which only two atoms are trapped so we can observe individual atom loss events. A numerical model of the complex dynamics of the expelling process agrees well with our experiment. We find that the light-assisted collisions can lead to j...

Rapid Production of Uniformly Filled Arrays of Neutral Atoms

“…Using optical tweezers, long-range interactions between neutral atoms have been harnessed via Rydberg blockade [3-5], and it is now possible to observe controlled interactions and interference between bosonic and fermionic atoms placed individually in their motional ground state [6][7][8]. While optical tweezer traps can be scaled to arrays [9][10][11][12], realizing an ordered array with a single atom per trap is difficult and is a problem of long-standing interest [13][14][15][16].Early experiments with optical tweezers demonstrated sub-Poissonian atom-number statistics using light-assisted collisions that rapidly expel pairs of atoms, a process known as collisional blockade [17][18][19][20]. This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17].…”

“…For comparison, single atoms can be loaded into our h × 23 MHz depth trap via PGC in 63% of attempts, as shown by the red bars in Fig. 1(d) [6,20,26].…”

“…Early experiments with optical tweezers demonstrated sub-Poissonian atom-number statistics using light-assisted collisions that rapidly expel pairs of atoms, a process known as collisional blockade [17][18][19][20]. This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17].…”

“…This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17]. However, the collisional blockade also limits loading efficiencies to approximately 50%, making the probability to uniformly-fill large arrays prohibitively small [18][19][20].…”

“…This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17]. However, the collisional blockade also limits loading efficiencies to approximately 50%, making the probability to uniformly-fill large arrays prohibitively small [18][19][20].Careful studies of light-assisted collisions in optical dipole traps hold promise for realizing deterministic loading of arrays of atoms [16,21]. Light-assisted collisions are successfully described by transitions between molecular potentials that become resonant with the light at specific interatomic separations, R C [ Fig.…”