Control of matter wave tunneling in an optical lattice

Bose Einstein condensation is a phase transition emerging in systems of integer-spin particles whose temperature is lowered under a critical value. One of the signatures of this phenomenon is the emergence of a phase coherence through the whole system, so that its behaviors can be de- scribed by single particle wavefunctions. After two-decades-long efforts in the development of laser cooling techniques, Bose-Einstein conden- sation was achieved in dilute gases of neutral atoms. Apart from its fundamental interest, this experimental result opened the way to the study of the quantum world with macroscopic samples. In parallel with the research on cooling, the developments on laser physics led to the creation of artificial atomic crystals by use of light-induced periodic potentials, so-called optical lattices. These potentials were applied to Bose-Einstein condensates shortly after their discovery. In the last decade, a large part of the BEC community showed a strong interest in ultra-cold atoms loaded into optical lattices. The periodic potentials proved to be an exceptional tool for manipulating BECs, because of their feasibility in the laboratory with the present technology, and be- cause only few parameters govern the behavior of the sample. In fact, this is described by the interplay between two fundamental physical processes: atom-atom interactions and quantum tunneling. The unifying theme of this thesis is the quantum tunneling in an ultra-cold gas loaded into an optical lattice. In the experiments that we performed we were able to observe effects due to quantum tunneling as well as to develop experimental techniques to control it

Coherent transport of cold atoms in angle-tuned optical lattices

Optical lattices with a large spacing between the minima of the optical potential can be created using the angle-tuned geometry where the 1-D periodic potential is generated by two propagating laser beams intersecting at an angle different from $\pi$. The present work analyzes the coherent transport for the case of this geometry. We show that the potential depth can be kept constant during the transport by choosing a magic value for the laser wavelength. This value agrees with that of the counterpropagating laser case, and the magic wavelength does not depend of the optical lattice geometry. Moreover, we find that this scheme can be used to implement controlled collision experiments under special geometric conditions. Finally we study the transport of hyperfine-Zeeman states of rubidium 87.Comment: 8 pages, 5 figures, one section added, in press in Phys. Rev.

Cold heteronuclear atom-ion collisions

We study cold heteronuclear atom ion collisions by immersing a trapped single ion into an ultracold atomic cloud. Using ultracold atoms as reaction targets, our measurement is sensitive to elastic collisions with extremely small energy transfer. The observed energy-dependent elastic atom-ion scattering rate deviates significantly from the prediction of Langevin but is in full agreement with the quantum mechanical cross section. Additionally, we characterize inelastic collisions leading to chemical reactions at the single particle level and measure the energy-dependent reaction rate constants. The reaction products are identified by in-trap mass spectrometry, revealing the branching ratio between radiative and non-radiative charge exchange processes

Hybrid quantum systems of atoms and ions

In recent years, ultracold atoms have emerged as an exceptionally controllable experimental system to investigate fundamental physics, ranging from quantum information science to simulations of condensed matter models. Here we go one step further and explore how cold atoms can be combined with other quantum systems to create new quantum hybrids with tailored properties. Coupling atomic quantum many-body states to an independently controllable single-particle gives access to a wealth of novel physics and to completely new detection and manipulation techniques. We report on recent experiments in which we have for the first time deterministically placed a single ion into an atomic Bose Einstein condensate. A trapped ion, which currently constitutes the most pristine single particle quantum system, can be observed and manipulated at the single particle level. In this single-particle/many-body composite quantum system we show sympathetic cooling of the ion and observe chemical reactions of single particles in situ.Comment: ICAP proceeding

A scalable hardware and software control apparatus for experiments with hybrid quantum systems

Modern experiments with fundamental quantum systems - like ultracold atoms, trapped ions, single photons - are managed by a control system formed by a number of input/output electronic channels governed by a computer. In hybrid quantum systems, where two or more quantum systems are combined and made to interact, establishing an efficient control system is particularly challenging due to the higher complexity, especially when each single quantum system is characterized by a different timescale. Here we present a new control apparatus specifically designed to efficiently manage hybrid quantum systems. The apparatus is formed by a network of fast communicating Field Programmable Gate Arrays (FPGAs), the action of which is administrated by a software. Both hardware and software share the same tree-like structure, which ensures a full scalability of the control apparatus. In the hardware, a master board acts on a number of slave boards, each of which is equipped with an FPGA that locally drives analog and digital input/output channels and radiofrequency (RF) outputs up to 400 MHz. The software is designed to be a general platform for managing both commercial and home-made instruments in a user-friendly and intuitive Graphical User Interface (GUI). The architecture ensures that complex control protocols can be carried out, such as performing of concurrent commands loops by acting on different channels, the generation of multi-variable error functions and the implementation of self-optimization procedures. Although designed for managing experiments with hybrid quantum systems, in particular with atom-ion mixtures, this control apparatus can in principle be used in any experiment in atomic, molecular, and optical physics.Comment: 10 pages, 12 figure

Design of a Littrow-type diode laser with independent control of cavity length and grating rotation

We present a novel, to the best of our knowledge, extended-cavity diode laser based on a modified Littrow configuration. The coarse wavelength adjustment via the rotation of a diffraction grating is decoupled from the fine tuning of the external cavity modes by positioning a piezo transducer behind the diode laser, making the laser robust against misalignment and hysteresis even with long external cavities. Two laser prototypes with external cavities of different lengths were tested with a 780 nm laser diode, and locked to an atomic reference. We observed a mode-hop-free frequency tunability broader than the free spectral range of the external cavity upon changes in its length. The design is well suited to atomic and molecular experiments demanding a high level of stability over time

Kinetics of a single trapped ion in an ultracold buffer gas

The immersion of a single ion confined by a radiofrequency trap in an ultracold atomic gas extends the concept of buffer gas cooling to a new temperature regime. The steady state energy distribution of the ion is determined by its kinetics in the radiofrequency field rather than the temperature of the buffer gas. Moreover, the finite size of the ultracold gas facilitates the observation of back-action of the ion onto the buffer gas. We numerically investigate the system's properties depending on atom-ion mass ratio, trap geometry, differential cross-section, and non-uniform neutral atom density distribution. Experimental results are well reproduced by our model considering only elastic collisions. We identify excess micromotion to set the typical scale for the ion energy statistics and explore the applicability of the mobility collision cross-section to the ultracold regime.Comment: 10 pages, 6 figure