Thomas Volz

Observation of molecules produced from a Bose-Einstein condensate.

Molecules are created from a Bose-Einstein condensate of atomic 87Rb using a Feshbach resonance. A Stern-Gerlach field is applied, in order to spatially separate the molecules from the remaining atoms. For detection, the molecules are converted back into atoms, again using the Feshbach resonance. The measured position of the molecules yields their magnetic moment. This quantity strongly depends on the magnetic field, thus revealing an avoided crossing of two bound states at a field value slightly below the Feshbach resonance. This avoided crossing is exploited to trap the molecules in one dimension.

Strongly correlated photons on a chip

Researchers observe a continuous change in photon correlations from strong antibunching to bunching by tuning either the probe laser or the cavity mode frequency. These results, which demonstrate unprecedented strong single-photon nonlinearities in quantum dot cavity system, are explained by the photon blockade and tunnelling in the anharmonic Jaynes–Cummings model.

Explanation of Photon Correlations in the Far-Off-Resonance Optical Emission from a Quantum-Dot-Cavity System

Martin Winger, Thomas Volz, Guillaume Tarel, Stefano Portolan, Antonio Badolato, Kevin J. Hennessy, Evelyn L. Hu, Alexios Beveratos, Jonathan Finley, Vincenzo Savona, and Ataç Imamoğlu Institute of Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne EPFL, CH-1015 Lausanne, Switzerland Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA California NanoSystems Institute, University of California, Santa Barbara, California 93106, USA CNRS Laboratoire Photonique et Nanostructures, Route de Nozay, F-91460 Marcoussis, France Walter Schottky Institut, Am Coulombwall 3, D-85748 Garching, Germany (Dated: November 23, 2009)

Feshbach resonances in rubidium 87: precision measurement and analysis.

More than 40 Feshbach resonances in rubidium 87 are observed in the magnetic-field range between 0.5 and 1260 G for various spin mixtures in the lower hyperfine ground state. The Feshbach resonances are observed by monitoring the atom loss, and their positions are determined with an accuracy of 30 mG. In a detailed analysis, the resonances are identified and an improved set of model parameters for the rubidium interatomic potential is deduced. The elastic width of the broadest resonance at 1007 G is predicted to be significantly larger than the magnetic-field resolution of the apparatus. This demonstrates the potential for applications based on tuning the scattering length.

Strong Dissipation Inhibits Losses and Induces Correlations in Cold Molecular Gases

Atomic quantum gases in the strong-correlation regime offer unique possibilities to explore a variety of many-body quantum phenomena. Reaching this regime has usually required both strong elastic and weak inelastic interactions because the latter produce losses. We show that strong inelastic collisions can actually inhibit particle losses and drive a system into a strongly correlated regime. Studying the dynamics of ultracold molecules in an optical lattice confined to one dimension, we show that the particle loss rate is reduced by a factor of 10. Adding a lattice along the one dimension increases the reduction to a factor of 2000. Our results open the possibility to observe exotic quantum many-body phenomena with systems that suffer from strong inelastic collisions.

Preparation of a quantum state with one molecule at each site of an optical lattice

Ultracold gases in optical lattices are of great interest, because these systems bear great potential for applications in quantum simulations and quantum information processing, in particular when using particles with a long-range dipole–dipole interaction, such as polar molecules1,2,3,4,5. Here we show the preparation of a quantum state with exactly one molecule at each site of an optical lattice. The molecules are produced from an atomic Mott insulator6 with a density profile chosen such that the central region of the gas contains two atoms per lattice site. A Feshbach resonance is used to associate the atom pairs to molecules7,8,9,10,11,12,13,14. The remaining atoms can be removed with blast light13,15. The technique does not rely on the molecule–molecule interaction properties and is therefore applicable to many systems.

Cavity quantum electrodynamics with charge-controlled quantum dots coupled to a fiber Fabry–Perot cavity

We demonstrate non-perturbative coupling between a single self-assembled InGaAs quantum dot and an external fiber-mirror-based microcavity. Our results extend the previous realizations of tunable microcavities while ensuring spatial and spectral overlap between the cavity mode and the emitter by simultaneously allowing for deterministic charge control of the quantum dots. Using resonant spectroscopy, we show that the coupled quantum dot cavity system is at the onset of strong coupling, with a cooperativity parameter of C ≈ 2.0 ± 1.3. Our results constitute a milestone in the progress toward the realization of a high-efficiency solid-state spin–photon interface.

Dissociation of ultracold molecules with Feshbach resonances

Ultracold molecules are associated from an atomic Bose-Einstein condensate by ramping a magnetic field across a Feshbach resonance. The reverse ramp dissociates the molecules. The kinetic energy released in the dissociation process is used to measure the widths of four Feshbach resonances in {sup 87}Rb. This method to determine the width works remarkably well for narrow resonances even in the presence of significant magnetic-field noise. In addition, a quasimonoenergetic atomic wave is created by jumping the magnetic field across the Feshbach resonance.

Feshbach blockade: Single-photon nonlinear optics using resonantly enhanced cavity polariton scattering from biexciton states

We theoretically demonstrate how the resonant coupling between a pair of cavity polaritons and a biexciton state can lead to a large single-photon Kerr nonlinearity in a semiconductor solid-state system. A fully analytical model of the scattering process between a pair of cavity polaritons is developed, which explicitly includes the biexcitonic intermediate state. A dramatic enhancement of the polariton-polariton interactions is predicted in the vicinity of the biexciton Feshbach resonance. Application to the generation of non-classical light from polariton dots is discussed.

Characterization of elastic scattering near a Feshbach resonance in 87Rb

The s-wave scattering length for elastic collisions between 87Rb atoms in the state |f,m_f>=|1,1> is measured in the vicinity of a Feshbach resonance near 1007 G. Experimentally, the scattering length is determined from the mean-field driven expansion of a Bose-Einstein condensate in a homogeneous magnetic field. The scattering length is measured as a function of the magnetic field and agrees with the theoretical expectation. The position and the width of the resonance are determined to be 1007.40 G and 0.20 G, respectively.