| 1. |
- Rehn, Magnus, 1972-, et al.
(författare)
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One-dimensional phase transitions in a two-dimensional optical lattice
- 2008
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 49:2, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- A phase transition for bosonic atoms in a two-dimensional anisotropic optical lattice is considered. If the tunnelling rates in two directions are different, the system can undergo a transition between a two-dimensional superfluid and a one-dimensional Mott insulating array of strongly coupled tubes. The connection to other lattice models is exploited in order to better understand the phase transition. Critical properties are obtained using quantum Monte Carlo calculations. These critical properties are related to correlation properties of the bosons and a criterion for commensurate filling is established.
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| 2. |
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| 3. |
- Ellmann, Harald, et al.
(författare)
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Experiments with a 3D double optical lattice
- 2003
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 90:5
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Tidskriftsartikel (refereegranskat)abstract
- We present a setup where we trap two different cesium hyperfine ground states in two different near-resonant optical lattices with identical topographies. We demonstrate that we can change the relative spatial phase between the lattices and we measure the equilibrium temperature as a function of the relative spatial phase. This provides a topographical chart of the optical potential. We also determine the rate at which atoms are transferred between the lattices and show that the setup is a promising candidate for implementing coherent quantum state manipulation.
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| 4. |
- Ellmann, H., et al.
(författare)
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Investigation and characterization of a 3D double optical lattice
- 2003
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Ingår i: European Physical Journal D. - : EDP Sciences. - 1434-6060 .- 1434-6079. ; 22:3, s. 355-364
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed description of measurements performed with a novel double optical lattice setup. In this we trap two different cesium hyperfine ground states in separate periodic potentials. A detailed account of the technical solutions and its foundations are given. We demonstrate the possibility to modulate the relative spatial position of the lattices and perform a series of systematic measurements in order to investigate the static and dynamic properties of the double optical lattice system.
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| 5. |
- Hagman, Henning, 1981-, et al.
(författare)
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Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:8, s. 83109-
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Tidskriftsartikel (refereegranskat)abstract
- A low noise time-of-flight detection system for laser cooled atoms has been constructed and incrementally optimized. Here, a thorough description of the construction is presented along with an analysis of the capabilities of the system. The quality of the detection (the resolution, the reproducibility, the sensitivity, etc.) is crucial for, e.g., the ability to see details in the velocity distribution profile, which is of interest for fundamental studies of statistical physics and of the laser cooling processes, and for detection of small initial velocities of an atomic cloud, important, e.g., when studying small drifts induced by Brownian motors and ratchets. We estimate the signal-to-noise ratio of our signal to be better than 1000:1 for a typical single shot, and we discuss the effect of the initial atomic cloud size, the probe size, and the effects of the wave packet spread during the fall time on the measured quantities. We show that the shape of the velocity distribution is well conserved during the mapping done in the detection, i.e., in the convolution with the probe beam, and that velocities as small as a few percent of the single photon recoil velocity can be resolved.
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| 6. |
- Hagman, Henning, 1981-, et al.
(författare)
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Directed transport with real-time external steering and drifts along pre-designed paths using a Brownian motor
- 2011
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 83:2
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Tidskriftsartikel (refereegranskat)abstract
- We have realized real-time steering of the directed transport in a Brownian motor based on cold atoms in optical lattices and demonstrate drifts along predesigned paths. The transport is induced by spatiotemporal asymmetries in the system, where we can control the spatial part, and we show that the response to changes in asymmetry is very fast. In addition to directional steering, a real-time control of the magnitude of the average drift velocity and an on-off switching of the motor are also demonstrated. We use a noninvasive real-time detection of the transport, enabling feedback control of the system.
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| 7. |
- Hagman, Henning, 1981-, et al.
(författare)
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Influence of the lattice topography on a three-dimensional, controllable Brownian motor
- 2008
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 81:3, s. 33001-
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Tidskriftsartikel (refereegranskat)abstract
- We study the influence of the lattice topography and the coupling between motion in different directions, for a three-dimensional Brownian motor based on cold atoms in a double optical lattice. Due to controllable relative spatial phases between the lattices, our Brownian motor can induce drifts in arbitrary directions. Since the lattices couple the different directions, the relation between the phase shifts and the directionality of the induced drift is non-trivial. Here is therefore this relation investigated experimentally by systematically varying the relative spatial phase in two dimensions, while monitoring the vertically induced drift and the temperature. A relative spatial phase range of 2pi x 2pi is covered. We show that a drift, controllable both in speed and direction, can be achieved, by varying the phase both parallel and perpendicular to the direction of the measured induced drift. The experimental results are qualitatively reproduced by numerical simulations of a simplified, classical model of the system.
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| 8. |
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| 9. |
- Jersblad, J., et al.
(författare)
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Anisotropic velocity distributions in 3D dissipative optical lattices
- 2003
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Ingår i: European Physical Journal D. - : EDP Sciences. - 1434-6060 .- 1434-6079. ; 22:3, s. 333-339
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Tidskriftsartikel (refereegranskat)abstract
- We present a direct measurement of velocity distributions in two dimensions by using an absorption imaging technique in a 3D near resonant optical lattice. The results show a clear difference in the velocity distributions for the different directions. The experimental results are compared with a numerical 3D semi-classical Monte-Carlo simulation. The numerical simulations are in good qualitative agreement with the experimental results.
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| 10. |
- Kastberg, Anders, 1963-, et al.
(författare)
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A three-dimensional Brownian motor, realised with symmetric optical lattices
- 2009
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 246:5, s. 999-1005
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional Brownian motor is realised using lasercooled caesium atoms trapped in a system of two static, and individually symmetric, optical lattices; a so-called double optical lattice. Isotropic fluctuations, emanating from light scattering, are rectified, and the diffusion of the ensemble of atoms is biased, with a resulting constant velocity that is controllable both in direction and magnitude. The working principle of the Brownian motor can be seen as a pulsation between two different potentials, both symmetric but around different points. The correlation between interferometric spatial offsets, and imbalance in optical pumping rates, leads to a spatio-temporal asymmetry sufficient for generating a controlled, directed motion.
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