Incommensurable matter-wave jets in quasi-1D geometry

We experimentally show the formation of incommensurable "golden" $\frac{1+\sqrt{5}}{2}$ matter-wave jets in a Bose-Einstein condensate (BEC) subjected to single frequency interaction modulation. We study the formation of higher order jets and the corresponding incommensurable density waves in quasi one dimensional (1D) geometry with the help of numerical 1D Gross-Pitaevskii equation simulation. We explore the process of jet formation experimentally and theoretically for a large range of modulation amplitudes and frequencies and present a phase diagram for jet formation. In simulation, for large modulation amplitudes, the distribution of jet velocities forms a supercontinuum, which emerges from the observed incommensurable matter-wave jets.Comment: 5 pages, 3 figures, improved versio

The use of optical tweezers in experiments with cold atoms and Bose-Einstein condensate

V magistrski nalogi predstavimo uporabo optične pincete za eksperimente s hladnimi atomi in Bose-Einsteinovim kondenzatom. Na začetku predstavimo lastnosti Bose-Einsteinovih kondenzatov ter hlajenje atomov z laserskim hlajenjem in hlajenjem z izhlapevanjem. Teoretično obravnavamo optične dipolne pasti in interferenco dveh Bose-Einsteinovih kondenzatov. V nadaljevanju opišemo delovanje optične pincete in predstavimo meritev frekvence nihanja atomov v pasti optične pincete. V naslednjem poglavju predstavimo eksperimente. Demonstriramo hlajenje z izhlapevanjem v pasti optične pincete ter prenos iz statične dipolne pasti v optično pinceto. Izvedemo eksperimente premikanja in razcepa kondenzatov in oblakov hladnih atomov. V nadaljevanju prikažemo meritev interference dveh kondenzatov. Nazadnje obravnavamo kondenzat v škatlastem potencialu, pripravljenim z optično pinceto. Na kondenzatu, pripravljenem v škatlastem potencialu, opazujemo nastanek solitonskih vlakov in odziv kondenzata na periodično modulacijo sipalne dolžine.This thesis presents the use of optical tweezers in experiments with cold atoms and Bose-Einstein condensate. First, we describe the properties of Bose-Einstein condensates and cooling of atoms with laser and evaporative cooling. We theoretically discuss optical dipole traps and the interference of two Bose-Einstein condensates. Next, we describe the operation of optical tweezers and present the measurement of the frequency of oscillations of atoms in an optical tweezer trap. In the next chapter, we present our experiments. Evaporative cooling in optical tweezers and the transfer of atoms from a static dipole trap to optical tweezers are demonstrated. Experiments of moving and splitting condensates and clouds of cold atoms are presented. Furthermore, we show the interference of two condensates. Finally, we observe a condensate in a box-like potential prepared with optical tweezers. In this set-up, we study the emergence of soliton trains and the response of the condensate to a periodic modulation of the scattering length

Preparation of ultra-cold atomic-ensemble arrays using time-multiplexed optical tweezers

We use optical tweezers based on time-multiplexed acousto-optic deflectors to trap ultra-cold cesium atoms in one-dimensional arrays of atomic ensembles. For temperatures between 2.5 $\mu$K and 50 nK we study the maximal time between optical tweezer pulses that retains the number of atoms in a single trap. This time provides an estimate on the maximal number of sites in an array of time-multiplexed optical tweezers. We demonstrate evaporative cooling of atoms in arrays of up to 25 optical tweezer traps and the preparation of atoms in a box potential. Additionally, we demonstrate three different protocols for the preparation of atomic-ensemble arrays by transfer from an expanding ultra-cold atomic cloud. These result in the preparation of arrays of up to 74 atomic ensembles consisting of $\sim$100 atoms on average.Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev.

Suppression of dark-state polariton collapses in cold-atom quantum memory

We observe dark-state polariton collapses and revivals in a quantum memory based on electromagnetically induced transparency on a cloud of cold cesium atoms in a magnetic field. Using $\sigma^+$ polarized signal and control beams in the direction of the magnetic field, we suppress the dark-state polariton collapses by polarizing the atoms towards one of the stretched Zeeman states and optimizing the frequency detuning of the control beam. In this way, we demonstrate a quantum memory with only partial dark-state polariton collapses, making the memory usable at any storage time, not only at discretized times of revivals. We obtain storage time of more than 400 $\rm{\mu}$s, which is ten times longer than what we can achieve by trying to annul the magnetic field.Comment: 6 pages, 4 figure