Cold collisions of ground- and excited-state alkali-metal atoms

Julienne, Paul S.; Vigué, J.

doi:10.1103/physreva.44.4464

Cited by 170 publications

(164 citation statements)

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“…In this example, the chirp extends from 800 to 100 MHz below the asymptote, exciting atom pairs to the 0 u potential over the range R 517a 0 to 1034a 0 . sufficient kinetic energy (e.g., 1 K per atom) before spontaneous emission occurs, the atom pair will be ejected from the trap [21,22]. Since the atoms are ultracold (e.g., 50 K), their motion on the ground state is minimal on the nanosecond time scale of the chirp.…”

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confidence: 99%

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Control of Ultracold Collisions with Frequency-Chirped Light

Wright

Gensemer²,

Vala

et al. 2005

Phys. Rev. Lett.

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We report on ultracold atomic collision experiments utilizing frequency-chirped laser light. A rapid chirp below the atomic resonance results in adiabatic excitation to an attractive molecular potential over a wide range of internuclear separation. This leads to a transient inelastic collision rate which is large compared to that obtained with fixed-frequency excitation. The combination of high efficiency and temporal control demonstrates the benefit of applying the techniques of coherent control to the ultracold domain. DOI: 10.1103/PhysRevLett.95.063001 PACS numbers: 32.80.Pj, 32.80.Qk, 34.50.Rk The ability to control the dynamics of microscopic systems has been a major motivation in physics and chemistry in recent years [1]. The development of ultrafast lasers and pulse-shaping techniques has allowed selective bond breaking and coherent control of chemical reactions [2]. At the other temporal extreme, slow collisions between ultracold atoms [3,4] can be controlled by long-range laser excitation because the colliding atoms have minimal kinetic energy and their trajectories are easily manipulated. In the present work, we adapt the techniques of coherent control to the nanosecond time scale and use frequencychirped light to control inelastic collisions between ultracold atoms. The combination of adiabatic excitation and the large number of atom pairs addressed by the chirp leads to a large transient collision rate. Such extensions of coherent control to the ultracold domain may significantly benefit processes such as ultracold molecule formation [5,6]. As an example, chirped two-photon Raman photoassociation [7,8] may provide an attractive alternative to magnetic Feshbach resonances for the coherent conversion of an atomic Bose-Einstein condensate into a molecular one. Because light can be controlled much faster than magnetic fields, the chirped excitation techniques developed here may allow the probing of quantum gases on much shorter time scales than previously achieved [9].There have been a number of experiments exploring the temporal dynamics of ultracold collisions. A long-lived ground-state shape resonance has been probed by timedependent photoassociation [10,11], and laser-induced collisions have been followed in real time [12,13]. Motivated by earlier predictions [14], photoassociative ionization dynamics on the nanosecond time scale have been probed with picosecond pulses [15]. In ultracold highly excited Rydberg atoms, the microsecond-scale evolution of resonant energy transfer has been observed via field ionization [16,17]. Our use of rapidly frequency-chirped laser light brings a new dimension to these studies. The temporal evolution of the light can lead to an efficient and robust adiabatic transfer of population to the excited state. Also, the wide range of frequencies spanned by the chirp leads to excitation of atom pairs over a wide range of internuclear separations. The advantages of chirped excitation have been discussed in the context of ultracold atom photoassociation with picosecond puls...

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“…In Fig. 2(a), the calculated transfer of population [18,23] from the ground state to the 0 u excited-state potential [22], neglecting hyperfine structure, is shown. Note that the center of the wave packet is resonant at a chirp detuning ÿ32:8 MHz.…”

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confidence: 99%

Control of Ultracold Collisions with Frequency-Chirped Light

Wright

Gensemer²,

Vala

et al. 2005

Phys. Rev. Lett.

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“…1) [18,19]. The |S + S asymptote represents two ground state atoms and |S + P represents one ground and one excited state atom.…”

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

et al. 2013

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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...

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“…Our first attempt used a semiclassical quasistatic model to examine the detailed molecular mechanisms for trap loss collisions in alkali species [34]. Predictions were made for Li, Na, K, Rb, and Cs traps, and good agreement was found with measurements on a Cs MOT.…”

Section: Supplemental Collisions Program: Theorymentioning

confidence: 99%

Laser Cooling and Trapping of Neutral Atoms

Phillips¹

1992

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Cold collisions of ground- and excited-state alkali-metal atoms

Cited by 170 publications

References 89 publications

Control of Ultracold Collisions with Frequency-Chirped Light

Control of Ultracold Collisions with Frequency-Chirped Light

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

Laser Cooling and Trapping of Neutral Atoms

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