Coherently driven three-level atoms in an optical cavity

We experimentally realize strong light-matter coupling of a single cesium atom to a single mode of a high-finesse optical cavity. In this regime, the optical properties of one atom change the transmission spectrum of the resonator significantly. The two hyperfine ground states of cesium can be distinguished by the relative transmission of a weak probe beam coupled to the cavity. Here, we coherently couple the two hyperfine ground states via an electronically excited state with two-photon transitions. In the first experimental configuration, two-photon Raman transitions are driven between the two ground states while continuously observing the atomic state. I present a new in-situ spectroscopic technique for the internal hyperfine and Zeeman-sublevel dynamics of an atom inside the cavity mode, using time-dependent Bayesian analysis of quantum jumps. In the second configuration, the three-level atomic structure forms the basis of Electromagnetically Induced Transparency (EIT). The modification of the absorptive and dispersive properties of an atom by destructive interference leads to strong changes in the transmission of the probe beam. Our observations are qualitatively described in a semiclassical picture in the weak-probing limit. I furthermore present a fully quantum mechanical model, where deviations from the weak-probing limit, dephasing effects and other hyperfine states are taken into account to fit our data quantitatively. Moreover, I formulated an extension of the semiclassical model to highlight a conceptual contrast to the quantum model. Additionally, the EIT effect is connected with a strong cooling effect, resulting in a 20-fold increase of the storage time of the atoms inside the cavity. I present further results of investigations of this effect where the atoms are trapped and EIT-cooled outside the cavity. From microwave sideband spectra it can be inferred that almost 80% of the atoms are in the ground state of motion along the trap axis

Light-Mediated Collective Atomic Motion in an Optical Lattice Coupled to a Membrane

We observe effects of collective atomic motion in a one-dimensional optical lattice coupled to an optomechanical system. In this hybrid atom-optomechanical system, the lattice light generates a coupling between the lattice atoms as well as between atoms and a micromechanical membrane oscillator. For large atom numbers we observe an instability in the coupled system, resulting in large-amplitude atom-membrane oscillations. We show that this behavior can be explained by light-mediated collective atomic motion in the lattice, which arises for large atom number, small atom-light detuning and asymmetric pumping of the lattice, in agreement with previous theoretical work. The model connects the optomechanical instability to a phase delay in the global atomic back-action onto the lattice light, which we observe in a direct measurement.Comment: new introduction, title and outlook; small modifications of the main text and figure

Sympathetic cooling of a membrane oscillator in a hybrid mechanical-atomic system

Sympathetic cooling with ultracold atoms and atomic ions enables ultralow temperatures in systems where direct laser or evaporative cooling is not possible. It has so far been limited to the cooling of other microscopic particles, with masses up to $90$ times larger than that of the coolant atom. Here we use ultracold atoms to sympathetically cool the vibrations of a Si$_3$N$_4$ nanomembrane, whose mass exceeds that of the atomic ensemble by a factor of $10^{10}$. The coupling of atomic and membrane vibrations is mediated by laser light over a macroscopic distance and enhanced by placing the membrane in an optical cavity. We observe cooling of the membrane vibrations from room temperature to $650\pm 230$ mK, exploiting the large atom-membrane cooperativity of our hybrid optomechanical system. Our scheme enables ground-state cooling and quantum control of low-frequency oscillators such as nanomembranes or levitated nanoparticles, in a regime where purely optomechanical techniques cannot reach the ground state.Comment: 11 pages, 4 figure

Optical control of the refractive index of a single atom

We experimentally demonstrate the elementary case of electromagnetically induced transparency (EIT) with a single atom inside an optical cavity probed by a weak field. We observe the modification of the dispersive and absorptive properties of the atom by changing the frequency of a control light field. Moreover, a strong cooling effect has been observed at two-photon resonance, increasing the storage time of our atoms twenty-fold to about 16 seconds. Our result points towards all-optical switching with single photons

Bayesian feedback control of a two-atom spin-state in an atom-cavity system

We experimentally demonstrate real-time feedback control of the joint spin-state of two neutral Caesium atoms inside a high finesse optical cavity. The quantum states are discriminated by their different cavity transmission levels. A Bayesian update formalism is used to estimate state occupation probabilities as well as transition rates. We stabilize the balanced two-atom mixed state, which is deterministically inaccessible, via feedback control and find very good agreement with Monte-Carlo simulations. On average, the feedback loops achieves near optimal conditions by steering the system to the target state marginally exceeding the time to retrieve information about its state.Comment: 4 pages, 4 figure

Phase and space resolved optical emission spectroscopic investigations of an inductively coupled RF plasma using an imaging acousto-optic spectrometer

Abstract A novel acousto-optic spectrometer (IfU Diagnostic Systems GmbH) for 2-dimensional (2D) optical emission spectroscopy with high spectral resolution has been developed. The spectrometer is based on acousto-optic tuneable filter technology with fast random wavelength access. Measurements for characterisation of the imaging quality, the spatial resolution, and the spectral resolution are presented. The applicability for 2D-space and phase resolved optical emission spectroscopy (2D-PROES) is shown. 2D-PROES has been applied to an inductively coupled plasma with radio frequency excitation at 13.56 MHz. D 2005 Published by Elsevier B.V

Analyzing quantum jumps of one and two atoms strongly coupled to an optical cavity

We induce quantum jumps between the hyperfine ground states of one and two Cesium atoms, strongly coupled to the mode of a high-finesse optical resonator, and analyze the resulting random telegraph signals. We identify experimental parameters to deduce the atomic spin state nondestructively from the stream of photons transmitted through the cavity, achieving a compromise between a good signal-to-noise ratio and minimal measurement-induced perturbations. In order to extract optimum information about the spin dynamics from the photon count signal, a Bayesian update formalism is employed, which yields time-dependent probabilities for the atoms to be in either hyperfine state. We discuss the effect of super-Poissonian photon number distributions caused by atomic motion.Comment: 12 pages, 13 figure