Electric-field induced dipole blockade with Rydberg atoms

High resolution laser Stark excitation of np (60 < n < 85) Rydberg states of ultra-cold cesium atoms shows an efficient blockade of the excitation attributed to long-range dipole-dipole interaction. The dipole blockade effect is observed as a quenching of the Rydberg excitation depending on the value of the dipole moment induced by the external electric field. Effects of eventual ions which could match the dipole blockade effect are discussed in detail but are ruled out for our experimental conditions. Analytic and Monte-Carlo simulations of the excitation of an ensemble of interacting Rydberg atoms agree with the experiments indicates a major role of the nearest neighboring Rydberg atom.Comment: 4 page

Efficient formation of deeply bound ultracold molecules probed by broadband detection

Using a non-selective broadband detection scheme we discovered an efficient mechanism of formation of ultracold Cs$_2$ molecules in deeply bound levels ($v=1-9$) of their electronic ground state X$^1 \Sigma_g^+$. They are formed by a one-photon photoassociation of ultracold cesium atoms in a manifold of excited electronic states, followed by a two-step spontaneous emission cascade. We were able to form about $10^5-10^6$ molecules per second in these low vibrational levels of the ground state. This detection scheme could be generalized to other molecular species for the systematic investigation of cold molecule formation mechanisms.Comment: 4 page

Rydberg excitation of a Bose-Einstein condensate

We have performed two-photon excitation via the 6P3/2 state to n=50-80 S or D Rydberg state in Bose-Einstein condensates of rubidium atoms. The Rydberg excitation was performed in a quartz cell, where electric fields generated by plates external to the cell created electric charges on the cell walls. Avoiding accumulation of the charges and realizing good control over the applied electric field was obtained when the fields were applied only for a short time, typically a few microseconds. Rydberg excitations of the Bose-Einstein condensates loaded into quasi one-dimensional traps and in optical lattices have been investigated. The results for condensates expanded to different sizes in the one-dimensional trap agree well with the intuitive picture of a chain of Rydberg excitations controlled by the dipole-dipole interaction. The optical lattice applied along the one-dimensional geometry produces localized, collective Rydberg excitations controlled by the nearest-neighbour blockade.Comment: 7 pages, 7 figures, Laser Physics in press. arXiv admin note: text overlap with arXiv:1103.423

Photoionization spectroscopy of excited states of cold cesium dimers

Photoionization spectroscopy of cold cesium dimers obtained by photoassociation of cold atoms in a magneto-optical trap is reported here. In particular, we report on the observation and on the spectroscopic analysis of all the excited states that have actually been used for efficient detection of cold molecules stabilized in the triplet a^3Sigma_u^+ ground state. They are: the (1)^3Sigma_g^+ state connected to the 6s+6p asymptote, the (2)^3Sigma_g^+ and (2)^3Pi_g states connected to the 6s+5d asymptote and finally the (3)^3Sigma_g^+ state connected to the 6s + 7s asymptote. The detection through these states spans a wide range of laser energies, from 8000 to 16500 cm-1, obtained with different laser dyes and techniques. Information on the initial distribution of cold molecules among the different vibrational levels of the a^3Sigma_u^+ ground state is also provided. This spectroscopic knowledge is important when conceiving schemes for quantum manipulation, population transfer and optical detection of cold cesium molecules.Comment: 24 pages, 11 figures. Note: tables are available separately. Accepted in Molecular Physic

Entanglement of two individual atoms using the Rydberg blockade

We report on our recent progress on the manipulation of single rubidium atoms trapped in optical tweezers and the generation of entanglement between two atoms, each individually trapped in neighboring tweezers. To create an entangled state of two atoms in their ground states, we make use of the Rydberg blockade mechanism. The degree of entanglement is measured using global rotations of the internal states of both atoms. Such internal state rotations on a single atom are demonstrated with a high fidelity.Comment: Proceeding of the 19th International Conference on Laser Spectroscopy ICOLS 2009, 7-13 June 2009, Hokkaido, Japa

Rydberg state mediated quantum gates and entanglement of pairs of neutral atoms

Experiments performed within the last year have demonstrated Rydberg state mediated quantum gates and deterministic entanglement between pairs of trapped neutral atoms. These experiments validate ten year old proposals for Rydberg mediated quantum logic, but are only the beginning of ongoing efforts to improve the fidelity of the results obtained and scale the experiments to larger numbers of qubits. We present here a summary of the results to date, along with a critical evaluation of the prospects for higher fidelity Rydberg gates.Comment: submitted to ICAP 2010 proceeding

Dark state experiments with ultracold, deeply-bound triplet molecules

We examine dark quantum superposition states of weakly bound Rb2 Feshbach molecules and tightly bound triplet Rb2 molecules in the rovibrational ground state, created by subjecting a pure sample of Feshbach molecules in an optical lattice to a bichromatic Raman laser field. We analyze both experimentally and theoretically the creation and dynamics of these dark states. Coherent wavepacket oscillations of deeply bound molecules in lattice sites, as observed in one of our previous experiments, are suppressed due to laser-induced phase locking of molecular levels. This can be understood as the appearance of a novel multilevel dark state. In addition, the experimental methods developed help to determine important properties of our coupled atom / laser system.Comment: 20 pages, 9 figure

Ion detection in the photoionization of a Rb Bose-Einstein condensate

Two-photon ionization of Rubidium atoms in a magneto-optical trap and a Bose-Einstein condensate (BEC) is experimentally investigated. Using 100 ns laser pulses, we detect single ions photoionized from the condenstate with a 35(10)% efficiency. The measurements are performed using a quartz cell with external electrodes, allowing large optical access for BECs and optical lattices.Comment: 14 pages, 7 figure