Efficient Grover search with Rydberg blockade

We present efficient methods to implement the quantum computing Grover search algorithm using the Rydberg blockade interaction. We show that simple pi-pulse excitation sequences between ground and Rydberg excited states readily produce the key conditional phase shift and inversion-about-the mean unitary operations for the Grover search. Multi-qubit implementation schemes suitable for different properties of the atomic interactions are identifed and the error scaling of the protocols with system size is found to be promising for immediate experimental investigation.Comment: Detailed description of algorithm for sub-register architecture. Error budget modified for Cs atomic parameters. To appear in J. Phys. B. Special Issue on Strong Rydberg interactions in ultracold atomic and molecular gase

Spatial quantum noise in singly resonant second-harmonic generation

We study the spatial distribution of quantum noise in singly resonant second-harmonic generation. Calculations are performed below threshold for spatial modulational instability. For parameters for which the intracavity fields are modulationally stable the spatial spectrum shows maximum squeezing at k=0, whereas under conditions of modulational instability we find maximum squeezing at finite wave number |k|=kc, where kc corresponds to the classical critical wave number

Efficient multiparticle entanglement via asymmetric Rydberg blockade

We present an efficient method for producing $N$ particle entangled states using Rydberg blockade interactions. Optical excitation of Rydberg states that interact weakly, yet have a strong coupling to a second control state is used to achieve state dependent qubit rotations in small ensembles. On the basis of quantitative calculations we predict that an N=8 Schr\"odinger cat state can be produced with a fidelity of 84% in cold Rb atoms.Comment: 3 figure

The drag of a body moving transversely in a confined stratified fluid

The slow motion of a body through a stratified fluid bounded laterally by insulating walls is studied for both large and small Peclet number. The Taylor column and its associated boundary and shear layers are very different from the analogous problem in a rotating fluid. In particular, the large Peclet number problem is non-linear and exhibits mixing of statically unstable fluid layers, and hence the drag is order one; whereas the small Peclet number flow is everywhere stable, and the drag is of the order of the Peclet number