We have constructed a novel optical trap for neutral atoms by using a Laguerre-Gaussian (doughnut) beam whose frequency is blue detuned to the atomic transition. Laser-cooled rubidium atoms are trapped in the dark core of the doughnut beam with the help of two additional laser beams which limit the atomic motion along the optical axis. About 10 8 atoms are initially loaded into the trap, and the lifetime is 150 ms. Because the atoms are confined at a point in a weak radiation field in the absence of any external field, ideal circumstances are provided for precision measurements. The trap opens the way to a simple technique for atom manipulation, including Bose-Einstein condensation of gaseous atoms.[S0031-9007 (97)03456-X] PACS numbers: 32.80.Pj, 39.90. + d

Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.

We have developed a high-sensitivity superconducting sub-array module for an X-band active phased array antenna. This sub-array module can be assumed as a multichannel T/R module with 16 antenna elements. And the module also includes 16 transmitting (TX) channels and 16 receiving (RX) channels with high-Tc superconducting (HTS) filters. By means of this sub-array module, a high-sensitivity antenna can be easily available for wireless applications such as communication systems and radar systems. In this paper, we describe the newly developed X-band superconducting sub-array module that is applicable as a key component for an active phased array antenna. In particular, each Rx channel contains a cryogenic circuit that mainly consists of HTS filters and a low-noise amplifier (LNA) cooled at 77 K for low insertion loss and low internal noise. 16 cryogenic circuits are contained within a 100 mm×100 mm×36.5 mm vacuum chamber and cooled by a small cooler. By using HTS filters and cooling, noise temperature of the RX channels was reduced to less than 60 K and naturally the high-sensitivity X-band sub-array module was realized. Additionally, the features of the sub-array module, such as low amplitude deviation and good phase linearity, indicated that both TX channels and RX channels were appropriate for an active phased array antenna.

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