Slowing probe and conjugate pulses in potassium vapor using four wave mixing.

We present an experimental study on ultraslow propagation of matched optical pulses in nondegenerate four wave mixing (FWM) in hot potassium vapor. The main figures of merit, i.e. fractional delay and fractional broadening, are determined to be 1.1 and 1.2, respectively. The latter two are approximately constant for the broad range of the two photon detuning. Input probe pulses between 20 ns and 120 ns can be delayed within broad range of the gain. The results are compared with the preceding works for Rb and Na.

Dark Hanle resonances from selected segments of the Gaussian laser beam cross-section.

We present the Hanle EIT resonances obtained from the various segments of the Gaussian laser beam cross-section, selected by moving the small aperture (placed in front of the detector) radially along the laser beam. Significant differences in the Hanle lineshapes are observed depending on whether the central or outer parts of the Gaussian laser beam are detected. The line narrowing and two counter-sign peaks occur at outer, less intense parts of the beam. The theoretical model suggests that the EIT lineshapes in the laser wings are result of the interference of the laser light and coherently prepared atoms coming from the central part of the beam. By blocking the central part of the laser beam in front of the detector, narrower, and for high laser intensities, even more contrasted Hanle resonances are obtained.

Upward penetration of grains through a granular medium.

We study experimentally the creeping penetration of guest (percolating) grains through densely packed granular media in two dimensions. The evolution of the system of the guest grains during the penetration is studied by image analysis. To quantify the changes in the internal structure of the packing, we use Voronoï tessellation and a certain shape factor which is a clear indicator of the presence of different underlying substructures (domains). We first consider the impact of the effective gravitational acceleration on upward penetration of grains. It is found that the higher effective gravity increases the resistance to upward penetration and enhances structural organization in the system of the percolating grains. We also focus our attention on the dependence of the structural rearrangements of percolating grains on some parameters like polydispersity and the initial packing fraction of the host granular system. It is found that the anisotropy of penetration is larger in the monodisperse case than in the bidisperse one, for the same value of the packing fraction of the host medium. Compaction of initial host granular packing also increases anisotropy of penetration of guest grains. When a binary mixture of large and small guest grains is penetrated into the host granular medium, we observe size segregation patterns.

On non-vanishing amplitude of Hanle electromagnetically induced absorption in Rb.

Amplitude and linewidts of the Hanle EIA, obtained from transmission of the laser locked to closed F(g) ? F(e) = F(g) +1 transitions in (85)Rb and(87)Rb, have maximum values at few mW/cm2. Amplitude of the EIA reaches steady value different from zero for higher laser intensities, even for laser intensities of 40 mW/cm(2). Theoretical model of EIA, for the same atomic system as in the experiment, show that the laser intensity, at which maximum of amplitudes and widths occur, depends on the laser detuning. For smaller laser detuning of a few tens of MHz, EIA has a maximum and then vanishes at higher laser intensities. For larger laser detuning of the order of hundreds MHz (but still in the range of Doppler broadening) amplitude of the EIA has very broad maximum and remains above zero for intensities above 40 mW/cm(2). Such theoretical results indicate that Hanle absorption peak remains in the experimental results, regardless of the laser intensities, due to Doppler effect.

Excitation in low-current discharges and breakdown in He at low pressures and very high electric field to gas density ratios E/N.

We investigate optical emission from low-current discharges in He at very high electric field to gas density ratios E/N between parallel plate electrodes. We also determine the electrical breakdown and the voltage-current behavior at low currents. The E/N are 300 Td to 9 kTd (1 Td = 10(-21) V m2) at pressures times electrode separations p(0)d from 3 to 0.9 Torr cm. Absolute optical emission probabilities versus distance are determined for the 501.6 nm line (3 (1)P -->2 (1)S) and for the 587.6 nm line (3 (3)D -->2 (3)P) by reference to Boltzmann calculations at our lowest E/N and to published pressure dependent electron beam experiments. At E/N below 1 kTd, the emission follows the exponential growth of the electron density, while at above 7 kTd heavy particle excitation is evident near the cathode. Collisional transfer of excitation from the singlet to the triplet system dominates the 587.6 nm excitation. Comparisons of models with experiments show the importance of excitation and of electron production at the cathode by fast He atoms produced by charge transfer collisions of He+ with He. The breakdown voltage versus p(0)d is multivalued for p(0)d approximately 1.5 Torr cm. At currents below 100 microA and our lower E/N, the discharge voltage decreases linearly with current as expected for an increasing electron yield with ion energy and E/N at the cathode.

Experimental demonstration of a technique to generate arbitrary quantum superposition states of a harmonically bound spin-1/2 particle.

Using a single, harmonically trapped 9Be(+) ion, we experimentally demonstrate a technique for generation of arbitrary states of a two-level particle confined by a harmonic potential. Rather than engineering a single Hamiltonian that evolves the system to a desired final state, we implement a technique that applies a sequence of simple operations to synthesize the state.

Experimental demonstration of a controlled-NOT wave-packet gate.

We report the experimental demonstration of a controlled-NOT (CNOT) quantum logic gate between motional and internal-state qubits of a single ion where, as opposed to previously demonstrated gates, the conditional dynamics depends on the extent of the ion's wave packet. Advantages of this CNOT gate over one demonstrated previously are its immunity from Stark shifts due to off-resonant couplings and the fact that an auxiliary internal level is not required. We characterize the gate logic through measurements of the postgate ion state populations for both logic basis and superposition input states, and we demonstrate the gate coherence via an interferometric measurement.