High Density Mesoscopic Atom Clouds in a Holographic Atom Trap

We demonstrate the production of micron-sized high density atom clouds of interest for meso- scopic quantum information processing. We evaporate atoms from 60 microK, 3x10^14 atoms/cm^3 samples contained in a highly anisotropic optical lattice formed by interfering di racted beams from a holographic phase plate. After evaporating to 1 microK by lowering the con ning potential, in less than a second the atom density reduces to 8x10^13 cm^- 3 at a phase space density approaching unity. Adiabatic recompression of the atoms then increases the density to levels in excess of 1x10^15 cm^-3. The resulting clouds are typically 8 microns in the longest dimension. Such samples are small enough to enable mesoscopic quantum manipulation using Rydberg blockade and have the high densities required to investigate new collision phenomena.Comment: 4 pages, 4 figures, submitted to PR

EUV Sunspot Plumes Observed with SOHO

Bright EUV sunspot plumes have been observed in five out of nine sunspot regions with the Coronal Diagnostic Spectrometer -- CDS on SOHO. In the other four regions the brightest line emissions may appear inside the sunspot but are mainly concentrated in small regions outside the sunspot areas. These results are in contrast to those obtained during the Solar Maximum Mission, but are compatible with the Skylab mission results. The present observations show that sunspot plumes are formed in the upper part of the transition region, occur both in magnetic unipolar-- and bipolar regions, and may extend from the umbra into the penumbra.Comment: 8 pages, 3 figures, to be published in ApJ Letter

Dynamics of Low-Density Ultracold Rydberg Gases

Population dynamics in weakly-excited clouds of ultracold $^{87}$Rb Rydberg atoms were studied by means of trap loss, fluorescence detection, and state dependent stimulated emission. Rydberg atoms were excited to various nl Rydberg states via continuous two-photon excitation from a magneto-optical trap. A stimulated emission probe laser was then used to bring the Rydberg atoms down to the 6P$_{3/2}$ state, allowing state-dependent detection of the Rydberg atoms. Measurements of trap loss and fluorescent emission reveal information about the evolution of the Rydberg populations. In particular, population in the initial Rydberg state quickly transfers to other Rydberg states by a non-collisional mechanism, likely superradiant emission. The trap-loss measurements are consistent with black-body ionization as the dominant loss mechanism.Comment: 9 pages, 7 figure

Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency <I>f<sub>H</sub></I> was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ). The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the London-Tromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland), the European Incoherent Scatter (EISCAT) UHF radar at Tromsø and the Tromsø ionosonde (dynasonde). The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation of striations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization

Assessment of hazardous air pollutants for advanced power systems

The 1990 Clean Air Act Amendments (CAAA) identified 189 substances as air toxics or hazardous air pollutants (HAPs). Under the CAAA, the US Environmental Protection Agency (EPA) must regulate emissions of these HAPs at their sources, including advanced power systems used for the production of electricity. This project focused on evaluating and manipulating the advanced power systems HAP data currently available for presentation to the US Department of Energy (DOE). The data were analyzed for trends associated with emission control systems and operating conditions. This project was an addition to an existing DOE program entitled Trace Element Emissions (TEE), which is being conducted by the Energy and Environmental Research Center (EERC). The purpose of this addition is to evaluate the current results of HAP emissions sampling from full-scale and demonstration units employing advanced power or hot-gas cleanup systems. The specific objectives of this program are to (1) perform a technical review and assessment of the data accumulated on the fate of trace metals in advanced coal power systems and compare them to emissions from conventional coal-fired power plants, and (2) assess the effectiveness of conventional and innovative control technologies relative to potential regulation requirements

Zeros of Rydberg-Rydberg Foster Interactions

Rydberg states of atoms are of great current interest for quantum manipulation of mesoscopic samples of atoms. Long-range Rydberg-Rydberg interactions can inhibit multiple excitations of atoms under the appropriate conditions. These interactions are strongest when resonant collisional processes give rise to long-range C_3/R^3 interactions. We show in this paper that even under resonant conditions C_3 often vanishes so that care is required to realize full dipole blockade in micron-sized atom samples.Comment: 10 pages, 4 figures, submitted to J. Phys.