Tesis doctoral de Stefan Rist
In the present thesis we study several schemes where the detection of the emitted light from an atomic ensemble gives information about the state of the atoms. a weak probe field drives the atoms such that its effect on the atomic evolution can be neglected. the scattered light is then measured as a function of various parameters such as scattering angle frequency intensity etc. the motivation for this route to investigate ultracold atomic gases is manifold. several theoretical works pointed out that the observation of photons scattered by ultracold atoms may provide complementary information on the quantum state of the atoms, which could be non-destructive in some setups. hence they may allow for feedback schemes, which ultimately could lead to quantum state transfer between the light and the atoms. another point is that optical detection gives in situ information about the state of the atomic ensemble. in chapter 1 we review the basic theory for the light matter interaction in second quantized. the theory presented in this chapter forms the basis for our investigations of light scattering from ensembles of ultracold atoms. we also make some comments about the validity of the approximations and possible ways for improvement. in chapter 2 we show how conservative potentials for the atoms, such as dispersive optical lattices, can be realized experimentally due to the dispersive interaction with a far detuned laser we then review some basic properties of the physics of a particle in a periodic potential. we show that the ground state and the lowest lying excitations of a bose-einstein condensate in a dispersive optical lattice can be described by the bose-hubbard hamiltonian. We end the chapter by presenting some theoretical techniques to perturbatively calculate the excitation spectrum and the eigenstates of the bose-hubbard hamiltonian, which will be used in the following chapters. in chapter 3 we study the photonic bandstructure of a chain of fixed pointlike atoms in a biperiodic configuration. We calculate the photonic spectra and the probe transmission if the atoms are in free space and inside a standing wave optical resonator, thereby extending the results of who considered the case of a monochromatic optical lattice. we study how the photonic spectra are modified as a function of the interparticle distance. By measuring the transmitted light signal we show how one can get information about the atomic configuration. we end the chapter with a discussion of the results obtained. in chapter 4 we consider light scattering from ultracold atoms in an optical lattice where we calculate the photonic scattering cross section as a function of energy and direction of emission along the mott-insulator-superfluid phase transition. we take into account the finite tunneling rate for the atoms, when evaluating the scattering cross section of the photons and the effect of photon recoil onto the atoms. The interference between the finite atomic tunneling rate and the photon induced hopping is visible in the heights of the bragg peaks and we show that this effect is measurable in the superfluid phase. we compare our analytical results using the techniques presented in chapter 2 with numerical results where we diagonalize exactly the bose hubbard hamiltonian for a small number of atoms and wells. we end the chapter with a discussion of our results. in chapter 5 we consider a gas of ultracold atoms trapped at two spatially separated regions in space. using a two raman lasers to couple atoms out of the systems we show that it is possible to measure the mean value of the atomic field operator of the two systems by measuring the scattered light intensity of one of the raman lasers. we compare our general theory to experimental results and find good qualitative agreement between experimental data and our theoretical results. we then show how this setup might be used to measure the temperature of a bose-einstein condensate and to monitor the superfluid to mott-insulator phase transition for a gas of ultracold atoms in an optical lattice. we end the chapter with a discussion of the results obtained.
Datos académicos de la tesis doctoral «Light propagation in ultracold atomic gases«
- Título de la tesis: Light propagation in ultracold atomic gases
- Autor: Stefan Rist
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 02/02/2011
Dirección y tribunal
- Director de la tesis
- Wolfgang Schleich
- Tribunal
- Presidente del tribunal: giovanna Morigi
- morgan Mitchell (vocal)
- Antonio Acin dal maschio (vocal)
- grigori Astrakharchik (vocal)