No Arabic abstract
We observe vacuum Rabi splitting in a lossy nearly confocal cavity indicating the strong coupling regime, despite a weak single-atom single-mode coupling. Strong collective interaction manifests itself in the typical $sqrt{N}$-dependence of the normal mode splitting on the number of atoms $N$. The $TEM_{00}$-mode coupling parameters are $(g,kappa,gamma)=2pitimes(0.12,0.8,2.6)$ MHz and up to $(1.33pm 0.08)times10^5$ cesium atoms were loaded into the mode volume.
We present experiments on ensemble cavity quantum electrodynamics with cold potassium atoms in a high-finesse ring cavity. Potassium-39 atoms are cooled in a two-dimensional magneto-optical trap and transferred to a three-dimensional trap which intersects the cavity mode. The apparatus is described in detail and the first observations of strong coupling with potassium atoms are presented. Collective strong coupling of atoms and light is demonstrated via the splitting of the cavity transmission spectrum and the avoided crossing of the normal modes.
We formulate a Bardeen-Cooper-Schriffer (BCS) theory of quasiparticles in a degenerate Fermi gas strongly coupled to photons in a optical cavity. The elementary photonic excitations of the system are cavity polaritons, which consist of a cavity photon and an excitation of an atom within the Fermi sea. The excitation of the atom out of the Fermi sea leaves behind a hole, which together results in a loosely bound Cooper pair, allowing for the system to be written by a BCS wavefunction. As the density of the excitations is increased, the excited atom and hole become more strongly bound, crossing over into the molecular regime. This thus realizes an alternative BCS to BEC crossover scenario, where the participating species are quasiparticle excitations in a Fermi sea consisting of excited atoms and holes.
We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron $^{173}$Yb atoms. By mapping the electronic states onto effective sites along a synthetic electronic dimension, we have engineered synthetic fermionic ladders with tunable magnetic fluxes. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the magnetic field flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.
We explore the asymmetric sequential Landau-Zener (LZ) dynamics in an ensemble of interacting Bose condensed two-level atoms coupled with a cavity field. Assuming the couplings between all atoms and the cavity field are identical, the interplay between atom-atom interaction and detuning may lead to a series of LZ transitions. Unlike the conventional sequential LZ transitions, which are symmetric to the zero detuning, the LZ transitions of Bose condensed atoms in a cavity field are asymmetric and sensitively depend on the photon number distribution of the cavity. In LZ processes involving single excitation numbers, both the variance of the relative atom number and the step slope of the sequential population ladder are asymmetric, and the asymmetry become more significant for smaller excitation numbers. Furthermore, in LZ processes involving multiple excitation numbers, there may appear asymmetric population ladders with decreasing step heights. During a dynamical LZ process, due to the atom-cavity coupling, the cavity field shows dynamical collapse and revivals. In comparison with the symmetric LZ transitions in a classical field, the asymmetric LZ transitions in a cavity field originate from the photon-number-dependent Rabi frequency. The asymmetric sequential LZ dynamics of Bose condensed atoms in a cavity field may open up a new way to explore the fundamental many-body physics in coupled atom-photon systems.
We experimentally demonstrate a ring geometry all-fiber cavity system for cavity quantum electrodynamics with an ensemble of cold atoms. The fiber cavity contains a nanofiber section which mediates atom-light interactions through an evanescent field. We observe well-resolved, vacuum Rabi splitting of the cavity transmission spectrum in the weak driving limit due to a collective enhancement of the coupling rate by the ensemble of atoms within the evanescent field, and we present a simple theoretical model to describe this. In addition, we demonstrate a method to control and stabilize the resonant frequency of the cavity by utilizing the thermal properties of the nanofiber.