Cooperativity in Highly Excited Rydberg
Ensembles — Control and Entanglement
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Storage and retrieval of optical photons in new experimental setupJuly 2015
Durham, UK

Recently, we completed building and optimisation of a new experimental apparatus to study strong and long-ranged interactions between optical photon stored as Rydberg excitations. The setup features two high numerical aperture lenses, allowing focusing of trapping and excitation lasers to less than 1 micrometre (lens assembly designed in collaboration with the Browaeys group, Palaiseau, COHERENCE collaboration). As the length scales are well below the Rydberg blockade, this allows the individual creation and addressing of single photons stored as Rydberg polaritons. We have created two microscopic cold atom clouds side-by-side (see figure 1) that serve as storage sites for individual photons.

We have recently achieved photon storage in this new apparatus (see figure 2) and will now look for interactions between photons in spatially separated channels which will increase the degree of control over the interactions compared to previous experiments. This can pave the way to applications such as a universal quantum gate for photonic qubits (see D. Parades Barato and C. S. Adams, Phys. Rev. Lett. 112 040501, 2014 for the proposed scheme).

Additionally, we were able to speed up the repetition rates in the new apparatus by two orders of magnitude thanks to the inclusion of a 2D MOT as atomic beam source (developed based on a design from the Weidemüller group, Heidelberg, COHERENCE collaboration).

Frequency comb 2015
TOPTICA, Graefelfing, Germany

We demonstrate and characterize an Er:fiber frequency comb with repetition rate of 80 MHz which is passively phase-stabilized via difference frequency generation (DFG). A universal method to measure the phase noise spectra of comb lines at different wavelengths is demonstrated. With repetition-rate stabilization to an RF oscillator a linewidth of below 100 kHz at 1550 nm is achieved. We have also demonstrated further reduction to the Hz level by locking the DFG comb to an optical reference. The measured phase noise spectra, after different nonlinear wavelength conversion stages, allow the analysis of noise properties in the laser system.

N. Hoghooghi, A. Sell, T. Puppe, R. Kliese, S. Falke, A. Zach and J. Stuhler, Frequency comb with Hz level line widthsICOLS 2015 22nd International Conference on Laser Spectroscopy June 28 - July 3 2015 Singapore , Centre for Quantum Technologies National University of Singapore, 129, (2015)
R. Kliese, A. Sell, F. Rohde, T. Puppe, A. Zach and W. G. Kaenders, Versatile characterization of a passively carrier envelope phase stable frequency comb sAbstract Book, 2015 Joint Conference of the IEEE IFCS a. EFTF, April 12-16, Denver, Colorado - USA, 248, (2015), ) , or see our full list of publications
From classical to quantum non-equilibrium dynamics of Rydberg excitations in optical lattices2015
Innsbruck, Austria

Ultracold atoms excited to Rydberg states are a powerful tool to study many-body physics. Strong and long-range interactions between Rydberg atoms leads to a spatially correlated and slowed down dynamics of Rydberg excitations: these phenomena are reminiscent of the relaxation of defects in the so-called One-Spin Facilitated Model, the minimal kinetically constrained model (KC) known to display glassy features. In particular, we encode the dynamical rules typical of KCs in the anti-blockade configuration, i.e. setting the laser detuning of the coupling between the ground-state and the Rydberg state to be exactly equal to the nearest-neighbour interaction between Rydberg-excited atoms. If in a certain region, an atom is already in the Rydberg state, a neighbouring atom will be "facilitated" to be also excited to the Rydberg state (see Figure below). Contrarily if, in the same region, no atom is in the Rydberg state, the Rydberg-excitation of any neighbouring atom is strongly suppressed by a large detuning. In the setup we propose, the coupling from the ground-state to an additional intermediate short-lived excited state can tune the regimes of the dynamics of Rydberg excitations. The two extremes are: the classical rate equation limit of the aforementioned One-Spin Facilitated Model and the coherent limit characterised by the rapid "cascaded" creation and destruction of clusters of Rydberg excitations with varying size from a preexisting isolated Rydberg excitation.

M. Mattioli, A. W. Glaetzle and W. Lechner, From classical to quantum non-equilibrium dynamics of Rydberg excitations in optical lattices, New Journal of Physics (submitted, 2015), or see our full list of publications
Resonant charge transfer of hydrogen Rydberg atoms2015
Oxford, UK

Hydrogen Rydberg atoms interacting with a surface undergo ionisaton by transferring the electron into the bulk. The electron transfer happens at surface-atom distances less than 5n2a0. For metal surfaces, the Rydberg electron energy is degenerate with the conduction band of the metal and resonant charge transfer can occur. For an electronically structured surface, a ‘band-gap metal’, charge transfer can only take place via discrete image states which form a series akin to the Rydberg series. Resonant enhancement of the surface ionisation is observed only for principal quantum numbers for which the Rydberg energy matches these image states. With this approach Hydrogen Rydberg atoms can be used to resolve high lying image states that were formerly inaccessible with other techniques.

J. A. Gibbard, M. Dethlefsen, M. Kohlhoff, C. J. Rennick, E. So, M. Ford and T. P. Softley, Resonant charge transfer of hydrogen Rydberg atoms incident at a Cu(100) projected band-gap surface, arXiv:1504.07191 (2015), or see our full list of publications

More research highlights
Highlights of the latest reseach into ultracold Rydberg atoms by COHERENCE network partners can be viewed on the following pages: