Cold collisions in a high-gradient magneto-optical trap

Ueberholz, B.; Kuhr, Stefan; Frese, Daniel; Gomer, V.; Meschede, Dieter

doi:10.1088/0953-4075/35/23/313

Cited by 26 publications

(21 citation statements)

References 32 publications

(62 reference statements)

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“…The model is presented in the Supplementary Information. Previous experiments with small samples of caesium atoms trapped in a high-gradient MOT identified a similar process, where only one atom was lost as a result of a light-assisted collision 26 . The existence of a similar process induced by red-detuned light and with lower probability in an optical dipole trap was predicted in ref.…”

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confidence: 82%

Near-deterministic preparation of a single atom in an optical microtrap

et al. 2010

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Neutral atoms stored in optical traps are strong candidates for a physical realization of a quantum logic device 1,2 . Far off-resonance optical traps provide conservative potentials and excellent isolation from the environment, and they may be arranged to produce arbitrary arrays of traps, where each trap is occupied by a single atom that can be individually addressed [3][4][5][6] . At present, significant effort is being expended on developing two-qubit gates based on coupling individual Rydberg atoms in adjacent optical microtraps [7][8][9] . A major challenge associated with this approach is the reliable generation of single-atom occupancy in each trap, as the loading efficiency in the past experiments has been limited to 50% (refs 4,7,8,10-12). Here we report a loading efficiency of 82.7% in an optical microtrap. We achieve this by manipulating the collisions between pairs of trapped atoms through tailored optical fields and directly observing the resulting single atoms in the trap.Deterministic control of single neutral atoms is a long-standing goal in atomic physics. Not only would it represent a milestone in scientists' ability to control the microscopic world, but also because it would enable a neutral-atom-based quantum logic device 7-9 . Two approaches have successfully led to direct observation of subPoissonian number distributions of atoms in optical microtraps, without consecutive atom sorting 13 . In the first, the Mott insulator transition of a Bose-Einstein condensate provides an efficient route for high occupancy of individual atoms in optical lattices where atoms can tunnel between adjacent lattice sites [14][15][16][17] . The second approach, which may be applied in arbitrary geometries 18,19 , is to employ light-assisted collisions 4,[10][11][12] . This method makes use of the change in the atom-atom interaction that arises when light drives one of the atoms undergoing a collision to the electronic excited state. In the case of light with a frequency below resonance (red detuned), the atom pair is excited to an attractive potential leading to the atoms forming a molecule and/or gaining a large amount of kinetic energy. In each case, both atoms are lost, leading to a maximal 50% chance of ending with one atom in the trap, depending on whether the initial atom number is even or odd 10,12 . However, a process where only one atom is lost as a result of a two-body collision would lead to deterministic preparation of a single atom in a given site. In the past, it has been shown that various forms of collisional trap loss can be suppressed by the application of optical control fields, and in particular, the use of blue-detuned light to effect so-called optical shielding 20,21 . In this Letter, we study light-assisted collisions at the single-event level. We prepare individual pairs of atoms in an optical microtrap and expose them to near-resonant light. We directly observe that light-assisted collisions between these atoms can lead to only one atom being lost. By choice of the frequency and intensi...

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confidence: 82%

Near-deterministic preparation of a single atom in an optical microtrap

et al. 2010

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“…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].…”

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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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“…We show here that with light that is blue-detuned from the single atom resonance, we can induce light-assisted collisions between pairs of atoms such that only one of the atoms is ejected from the microtrap [41]. To study these light-assisted collision processes directly, we trap pairs of atoms in a microtrap and monitor their decay when exposed to the blue-detuned probing beam.…”

Section: Introductionmentioning

confidence: 98%

Using light-assisted collisions to consistently isolate individual atoms for quantum information processing

Grünzweig

McGovern

Hilliard

et al. 2011

Quantum Inf Process

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We count a small number of atoms trapped in an optical microtrap, using fluorescence induced by a standing wave of blue-detuned light. Blue-detuned light limits losses from light-assisted collisions, allowing us to manipulate the trapped atoms further. When a pair of trapped atoms is detected in this way, we apply a tailored laser light pulse to induce light assisted-collisions. We directly observe that these collisions lead to either one or both atoms being lost from the microtrap. By optimizing the frequency and intensity of the laser beam inducing the light-assisted collisions, one atom loss can be made to dominate over pair loss. We demonstrate that in a microtrap occupied by ∼50 atoms, this optimized light-assisted collision pulse can eject all but one atom efficiently. This method may be used to prepare many singly occupied microtraps for a neutral atom based quantum computation device.

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Cold collisions in a high-gradient magneto-optical trap

Cited by 26 publications

References 32 publications

Near-deterministic preparation of a single atom in an optical microtrap

Near-deterministic preparation of a single atom in an optical microtrap

Trap-depth determination from residual gas collisions

Using light-assisted collisions to consistently isolate individual atoms for quantum information processing

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