Loading dynamics of optical trap and parametric excitation resonances of trapped atoms

Wu, Jin‐Wei; Newell, Raymond; Hausmann, M.; Vieira, D. J.; Zhao, Xinxin

doi:10.1063/1.2266164

Cited by 16 publications

(20 citation statements)

References 15 publications

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“…For trap depth determination of an optical dipole trap, measurements of beam waist and trap oscillation frequencies can be used to infer the depth. However, this procedure, as well as the interpretation of parametric heating experiments [43], can be complicated by the broadening and shift of the trap frequency and higher harmonics caused by the anharmonicity of the trapping potential [44][45][46]. A measurement of the differential ac Stark shift of the atoms in the dipole trap can provide a lower bound on trap depth so long as both the ground-and excited-state polarizabilites are well known.…”

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confidence: 99%

Trap-depth determination from residual gas collisions

et al. 2011

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We present a method for determining the depth of an atomic or molecular trap of any type. This method relies on a measurement of the trap loss rate induced by collisions with background gas particles. Given a fixed gas composition, the loss rate uniquely determines the trap depth. Because of the "soft" long-range nature of the van der Waals interaction, these collisions transfer kinetic energy to trapped particles across a broad range of energy scales, from room temperature to the microkelvin energy scale. The resulting loss rate therefore exhibits a significant variation over an enormous range of trap depths, making this technique a powerful diagnostic with a large dynamic range. We present trap depth measurements of a Rb magneto-optical trap using this method and a different technique that relies on measurements of loss rates during optical excitation of colliding atoms to a repulsive molecular state. The main advantage of the method presented here is its large dynamic range and applicability to traps of any type requiring only knowledge of the background gas density and the interaction potential between the trapped and background gas particles.The particle loss rate from a trap is one of the primary observables for probing the collisional physics of trapped gases. Measurements of trap loss are routinely made in a variety of experiments to deduce elastic and inelastic collision cross sections for intratrap collisions and for collisions between trapped species and externally introduced particles. Trap depth often plays an important role in the interpretation of these measurements. A well-studied example of this is the large intensity-dependent variation displayed by the two-body intratrap loss-rate coefficient for atoms trapped in a magnetooptical trap (MOT). This variation results from an interplay of trap depth and the energy imparted to trapped atoms due to hyperfine or fine structure changing collisions, as well as radiative escape [1][2][3][4][5][6][7][8][9][10][11][12]. More recently, inelastic and elastic collision rates in dipole traps have been of interest, particularly for metastable species [13,14]. The fraction of elastic collisions resulting in an evaporated atom depends on trap depth, which is a key parameter for evaporative cooling [13,15,16]. The lifetime dependence of a state-insenstive dipole trap on trap depth for cesium atoms has also recently been investigated [17]. Of course the most fundamental role of trap depth is that it be large enough to provide sufficient confinement, which has been an issue for experiments with buffer-gas-cooled atoms or molecules [18,19].In recent years there has been interest in making precision determinations of collision cross-sections from measurements of particle loss rates due to externally introduced particles. These measurements involve collisions of trapped neutral particles with neutral atoms and molecules [20][21][22][23][24], electron beams [25][26][27], and trapped ions [28][29][30]. Photoionization cross sections have also been investigated though mea...

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confidence: 99%

Trap-depth determination from residual gas collisions

et al. 2011

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“…Parametric excitation, in which the FORT power is modulated to excite parametric resonances in the atomic motion, is widely used to characterize the trap frequencies in optically-trapped atomic gases [30,31]. With ensembles the heating rate, and thus the rate of loss from the trap, shows resonances at specific frequencies.…”

Section: Parametric Resonances and Trap Frequencymentioning

confidence: 99%

“…In the harmonic approximation, these occur at double the trap frequencies, due to the even symmetry of the perturbation to the potential. Corrections due to trap anharmonicity have been studied [30] and the technique has been applied to single atoms [32].…”

Section: Parametric Resonances and Trap Frequencymentioning

confidence: 99%

“…Results are shown in Figure 7, with resonances at ≈ 12 kHz and ≈ 100 kHz, about 10 % lower than expected based on the trap frequencies previously estimated. We note that anharmonicity has not been taken into account, and can be expected to shift the parametric resonances to lower frequency relative to the second harmonics of the trap frequencies [30]. Also shown are the results of a MC simulation, in which atoms drawn from a Boltzmann distribution as in section III C are allowed to evolve under the modulated potential plus a Langevin term describing isotropic noise from scattering of background and FORT photons.…”

Section: Parametric Resonances and Trap Frequencymentioning

confidence: 99%

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Manipulating and measuring single atoms in the Maltese cross geometry

Bianchet¹,

Alves²,

Zarraoa³

et al. 2021

Preprint

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We describe optical methods for trapping, cooling, and observing single 87 Rb atoms in a four-lens "Maltese cross" geometry (MCG). The use of four high numerical-aperture lenses in the cardinal directions enables efficient collection of light from non-collinear directions, but also restricts the optical access for cooling and optical pumping tasks. We demonstrate three-dimensional atom localization with sub-wavelength precision, and present measurements of the trap lifetime, temperature and transverse trap frequency in this geometry. We observe a trap performance comparable to what has been reported for single-atom traps with one-or two-lens optical systems, and conclude that the additional coupling directions provided by the MCG come at little cost to other trap characteristics.

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“…In the situation presented in the current work, the optical trap is produced with a focused standing wave beam, where the atoms are constrained to within half a wavelength in the axial direction and more weakly by the transverse profile. In work by Wu et al, optical lattice trapping has been modelled, where it was assumed that all the atoms with kinetic energy less than the potential depth were trapped [22]. In our simulation we treat the ratio of lattice waist size to atomic cloud size as an adjustable parameter (relevant to most experiments), and compute the fraction of atoms remaining in the trap to investigate transfer efficiency.…”

Section: Introductionmentioning

confidence: 99%

Simulation of optical lattice trap loading from a cold atomic ensemble

Watson,

McFerran

2020

Preprint

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We model the efficiency of loading atoms of various species into a one dimensional optical lattice from a cold ensemble taking into account the initial cloud temperature and size, the lattice laser properties affecting the trapping potential, and atomic parameters. Stochastic sampling and dynamical evolution are used to simulate the transfer, leading to estimates of transfer efficiency for varying trap depth and profile. Tracing the motion of the atoms also enables the evaluation of the equilibrium temperature and site occupancy in the lattice. The simulation compares favourably against a number of experimental results, and is used to compute an optimum lattice-waist to cloud-radius ratio for a given optical power.

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Loading dynamics of optical trap and parametric excitation resonances of trapped atoms

Cited by 16 publications

References 15 publications

Trap-depth determination from residual gas collisions

Trap-depth determination from residual gas collisions

Manipulating and measuring single atoms in the Maltese cross geometry

Simulation of optical lattice trap loading from a cold atomic ensemble

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