Today on the archive
Tue Aug 1 09:26:12 BST 2006
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- Title: Fast cooling of trapped ions using the dynamical Stark shift gate
- Authors: Authors: A. Retzker, M.B. Plenio
- Abstract: A laser cooling scheme for trapped ions is presented which is based on the fast dynamical Stark shift gate, described in [Jonathan etal, PRA 62, 042307]. Since this cooling method does not contain an off resonant carrier transition, low final temperatures are achieved even in traveling wave light field. The proposed method may operate in either pulsed or continuous mode and is also suitable for ion traps using microwave addressing in strong magnetic field gradients.
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- Title: Intense ultrashort electromagnetic pulses and the equation of motion
- Authors: Richard T Hammond
- Abstract: The equations of motion of charged particles under the influence of short electromagnetic pulses are investigated. The subcycle regime is considered, and the delta function approximation is applied. The effects of the self force are also considered, and the threshold where radiation becomes important is discussed. A dimensionless parameter is defined that signals the onset of radiation reaction effects.
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- Title: Modelling optical micro-machines
- Authors: Vincent L. Y. Loke, Timo A. Nieminen, Agata M. Branczyk, Norman R. Heckenberg, Halina Rubinsztein-Dunlop
- Abstract: A strongly focused laser beam can be used to trap, manipulate and exert torque on a microparticle. The torque is the result of transfer of angular momentum by scattering of the laser beam. The laser could be used to drive a rotor, impeller, cog wheel or some other microdevice of a few microns in size, perhaps fabricated from a birefringent material. We review our methods of computationally simulating the torque and force imparted by a laser beam. We introduce a method of hybridizing the T-matrix with the Finite Difference Frequency Domain (FDFD) method to allow the modelling of materials that are anisotropic and inhomogeneous, and structures that have complex shapes. The high degree of symmetry of a microrotor, such as discrete or continuous rotational symmetry, can be exploited to reduce computational time and memory requirements by orders of magnitude. This is achieved by performing calculations for only a given segment or plane that is repeated across the whole structure. This can be demonstrated by modelling the optical trapping and rotation of a cube.
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- Title: Precision preparation of strings of trapped neutral atoms
- Authors: Y. Miroshnychenko, W. Alt, I. Dotsenko, L. Förster, M. Khudaverdyan, A. Rauschenbeutel, D. Meschede
- Abstract: We have recently demonstrated the creation of regular strings of neutral caesium atoms in a standing wave optical dipole trap using optical tweezers [Y. Miroshnychenko et al., Nature, in press (2006)]. The rearrangement is realized atom-by-atom, extracting an atom and re-inserting it at the desired position with sub-micrometer resolution. We describe our experimental setup and present detailed measurements as well as simple analytical models for the resolution of the extraction process, for the precision of the insertion, and for heating processes. We compare two different methods of insertion, one of which permits the placement of two atoms into one optical micropotential. The theoretical models largely explain our experimental results and allow us to identify the main limiting factors for the precision and efficiency of the manipulations. Strategies for future improvements are discussed.
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- Title: Optimization of segmented linear Paul traps and transport of stored particles
- Authors: Stephan Schulz, Ulrich Poschinger, Kilian Singer, Ferdinand Schmidt-Kaler
- Abstract: Single ions held in linear Paul traps are promising candidates for a future quantum computer. Here, we discuss a two-layer microstructured segmented linear ion trap. The radial and axial potentials are obtained from numeric field simulations and the geometry of the trap is optimized. As the trap electrodes are segmented in the axial direction, the trap allows the transport of ions between different spatial regions. Starting with realistic numerically obtained axial potentials, we optimize the transport of an ion such that the motional degrees of freedom are not excited, even though the transport speed far exceeds the adiabatic regime. In our optimization we achieve a transport within roughly two oscillation periods in the axial trap potential compared to typical adiabatic transports that take of the order 100 oscillations. Furthermore heating due to quantum mechanical effects is estimated and suppression strategies are proposed.
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- Title: Quantum coherence and population trapping in three-photon processes
- Authors: Caroline Champenois (PIIM), Giovanna Morigi (GRUP D'OPTICA), Juergen Eschner (ICFO)
- Abstract: The spectroscopic properties of a single, tightly trapped atom are studied, when the electronic levels are coupled by three laser fields in an $N$-shaped configuration of levels, whereby a $\Lambda$-type level system is weakly coupled to a metastable state. We show that depending on the laser frequencies the response can be tuned from coherent population trapping at two-photon resonance to novel behaviour at three photon resonance, where the metastable state can get almost unit occupation in a wide range of parameters. For certain parameter regimes the system switches spontaneously between dissipative and coherent dynamics over long time scales.
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