We show that Sisyphus cooling in a one-dimensional gray optical lattice can be improved by using a bichromatic standing wave that increases the efficiency of cooling as compared to typical lattices. Using the time of flight technique to determine the velocity distribution of all the atoms, we calculate the efficiency by measuring the fraction of all atoms that are cooled by the lattice. We show that the efficiency depends on the relative displacement between the two standing waves formed by the two colors. The optimal configuration of the bichromatic light field yields a 40% improvement in efficiency compared to typical optical lattices, while maintaining the same atomic temperature.
We show that Sisyphus cooling in a one-dimensional gray optical lattice can be improved by using a bichromatic standing wave that increases the efficiency of cooling as compared to typical lattices. Using the time of flight technique to determine the velocity distribution of all the atoms, we calculate the efficiency by measuring the fraction of all atoms that are cooled by the lattice. We show that the efficiency depends on the relative displacement between the two standing waves formed by the two colors. The optimal configuration of the bichromatic light field yields a 40% improvement in efficiency compared to typical optical lattices, while maintaining the same atomic temperature.
Optical lattices are periodic arrangements of laser cooled atoms trapped in potentials created by the interference of multiple laser beams. In this dissertation, we describe a series of experiments performed using optical lattices that exploit the coherence of atoms and we also look at new ways to cool the atoms. With a sudden shift of the optical lattice, atomic wavepackets can be created that evolve much like a classical particle. Using a photon redistribution technique, we have characterized the oscillation of wavepackets in the anharmonic potential wells. Atoms will quantum mechanically tunnel between lattice sites with a sufficiently shallow potential. Due to the structure of the optical lattices that are used, while the atom is tunneling, its internal angular momentum state must change. We use this change to detect and characterize the tunneling. The change in internal state leads to the formation of a new potential that acts on the atom, which is known as a gauge potential, which does not depend on the light intensity, but depends only on the geometry of the lattice. We have for the first time measured and characterized this gauge potential. Finally, by randomly modulating the lattice potential, we have demonstrated that tunneling can be suppressed. We have shown that an enhancement of the Sisyphus cooling process, which localizes atoms in the wells of an optical lattice, is possible using a bichromatic standing wave. A time of flight technique is used to verify the cooling improvement. We combine the techniques developed in these experiments and apply them to the cooling of the trapped atoms using a feedback mechanism, which is analogous to the well known technique of stochastic cooling in the field of beam physics. Lastly, we have laid the theoretical basis for using the ponderomotive force to create optical lattices for laser cooled Rydberg atoms. Rydberg atoms are attractive because of their many extreme properties, and the ability to trap Rydberg atoms into lattice sites will increase the range of experiments and measurements that can be made with them.
We propose a scheme for three-dimensional trapping and cooling of atoms in a bichromatic standing wave formed by two different longitudinal modes of an optical cavity. The atoms are cooled through an efficient Sisyphus mechanism and trapped at those anti-nodes (maxima) of the stronger field where the second weaker field has a node, this leading to a large effective atom-field coupling. Contrary to the case of a single strong standing wave, the final width of the momentum distribution is considerably less than the depth of the optical potential implying long storage times. The scheme offers the possibility of capturing atoms out of the background and achieving high local densities modulated with the beat frequency of the two involved modes. The results from a three-dimensional semi-classical calculation are confirmed by a full QMCWF simulation as well as by a quantum rate equation model in the one-dimensional case in the proper limits.
We present a calculation of cooling of Rydberg atoms in bichromatic standing light waves. The atoms in our model are assumed to have a cascade three-level transition scheme, with the second excited level being the Rydberg state. The cooling fields, which also excite the atoms to the Rydberg state, consist of two standing waves whose frequencies are tuned near the two transition frequencies of the cascade atomic system. It is shown that the mechanisms of Sisyphus cooling and velocity-selective coherent population trapping can co-exist in such a configuration, and under certain conditions the majority of the laser-cooled atoms are in the Rydberg state.
We demonstrate subrecoil Sisyphus cooling using the long-lived ^{3}P_{0} clock state in alkaline-earth-like ytterbium. A 1388-nm optical standing wave nearly resonant with the ^{3}P_{0}→^{3}D_{1} transition creates a spatially periodic light shift of the ^{3}P_{0} clock state. Following excitation on the ultranarrow clock transition, we observe Sisyphus cooling in this potential, as the light shift is correlated with excitation to ^{3}D_{1} and subsequent spontaneous decay to the ^{1}S_{0} ground state. We observe that cooling enhances the loading efficiency of atoms into a 759-nm magic-wavelength one-dimensional (1D) optical lattice, as compared to standard Doppler cooling on the ^{1}S_{0}→^{3}P_{1} transition. Sisyphus cooling yields temperatures below 200 nK in the weakly confined, transverse dimensions of the 1D optical lattice. These lower temperatures improve optical lattice clocks by facilitating the use of shallow lattices with reduced light shifts while retaining large atom numbers to reduce the quantum projection noise. This Sisyphus cooling can be pulsed or continuous and is applicable to a range of quantum metrology applications.
\n \nWe theoretically investigate an all optical scheme for three-dimensional \ntrapping and cooling of atoms in a single bichromatic standing \nwave with a Gaussian transverse intensity profile \nas, e.g. formed by two different longitudinal modes of a linear \noptical cavity. The atoms are cooled through an efficient Sisyphus \nmechanism and trapped at those anti-nodes (maxima) of the stronger \nfield where the second weaker field has a node. \nThis generates a large effective atom-field coupling as it is desired \nin nonlinear optical experiments with clouds of atoms. The scheme effects \nhigh local densities modulated at the beat frequency of the \ntwo involved modes. In the appropriate parameter regime the results \nfrom a three-dimensional semi-classical approach are confirmed by \na 1D full QMCWF-simulation. Extending our model to a \nmore realistic case, we include loss channels out of the system and repumping. \nFurthermore, we generalise our approach to Λ-type level schemes,\nwhich exhibit promising optical nonlinearities. Trapping and cooling \nof such atoms is predicted to be compatible with maintaining high \ncooperativities needed for large nonlinear effects.\n
A complete laser cooling setup was built, with focus on threedimensional near-resonant optical lattices for cesium. These consist of regularly ordered micropotentials, created by the interference of four laser beams. One key feature of optical lattices is an inherent ”Sisyphus cooling” process. It efficiently extracts kinetic energy from the atoms, leading to equilibrium temperatures of a few µK. The corresponding kinetic energy is lower than the depth of the potential wells, so that atoms can be trapped.We performed detailed studies of the cooling processes in optical lattices by using the time-of-flight and absorption-imaging techniques. We investigated the dependence of the equilibrium temperature on the optical lattice parameters, such as detuning, optical potential and lattice geometry. The presence of neighbouring transitions in the cesium hyperfine level structure was used to break symmetries in order to identify, which role “red” and “blue” transitions play in the cooling. We also examined the limits for the cooling process in optical lattices, and the possible difference in steady-state velocity distributions for different directions. Moreover, in collaboration with ´Ecole Normale Sup´erieure in Paris, numerical simulations were performed in order to get more insight in the cooling dynamics of optical lattices.Optical lattices can keep atoms almost perfectly isolated from the environment and have therefore been suggested as a platform for a host of possible experiments aimed at coherent quantum manipulations, such as spin-squeezing and the implementation of quantum logic-gates. We developed a novel way to trap two different cesium ground states in two distinct, interpenetrating optical lattices, and to change the distance between sites of one lattice relative to sites of the other lattice. This is a first step towards the implementation of quantum simulation schemes in optical lattices.