This paper presents the results of the observations of the detectors participating in the International Gravitational Event Collaboration (IGEC) from 1997 to 2000 and reviews the data analysis methods. The analysis is designed to search for coincident excitations in multiple detectors. The data set analyzed in this article covers a longer period and is more complete than that given in previous reports. The current analysis is more accurate for determining the false dismissal probability for a time coincidence search and it optimizes the search with respect to a target amplitude and direction of the signal. The statistics of the accidental coincidences agrees with the model used for drawing the results. The observations of this IGEC search are consistent with no detection of gravitational wave burst events. A new conservative upper limit has been set on the rate of gravitational wave bursts with a Fourier component $H>\mathrm{}2\mathrm{}\times {10}^{-21}{\mathrm{Hz}}^{-1},$ both for searches with and without a filter for the galactic center direction. This study confirms that the false alarm rate of the observation can be negligible when at least three detectors are operating simultaneously.

Recently, there has been a growing interest in integrated THz photonics for various applications in communications, spectroscopy and sensing. We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high-confinement waveguide layout planarized with a low-loss polymer. An extended top metallization keeps waveguide losses low while improving dispersion, thermal and RF properties, as it enables to decouple the design of THz and microwave cavities. Free-running on-chip quantum cascade laser combs spanning 800 GHz, harmonic states with over 1.1 THz bandwidth and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed using a homogeneous quantum-cascade active core. With a strong external RF drive, actively mode-locked pulses as short as 4.4 ps can be produced, as measured by SWIFTS. We demonstrate as well passive waveguides with low insertion loss, enabling the tuning of the laser cavity boundary conditions and the co-integration of active and passive elements on the same THz photonic chip.

We have measured the rate of thermally induced escape from the zero-voltage state in long Josephson junctions of both overlap and in-line geometry as a function of applied magnetic field. The statistical distribution of switching currents is used to evaluate the escape rate and derive an activation energy $\Delta U$ for the process. Because long junctions correspond to the continuum limit of multidimensional systems, $\Delta U$ is in principle the difference in energy between stationary states in an infinite-dimensional potential. We obtain good agreement between calculated and measured activation energies for junctions with lengths a few times the Josephson penetration depth ${\lambda }_J$.

The network of resonant bar detectors of gravitational waves resumed coordinated observations within the International Gravitational Event Collaboration (IGEC-2). Four detectors are taking part in this Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was the only gravitational wave observatory in operation. The implemented network data analysis is based on a time coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data was reserved for follow-up studies. The network amplitude sensitivity to bursts improved by a factor $\approx 3$ over the 1997-2000 IGEC observations; the wider sensitive band also allowed the analysis to be tuned over a larger class of waveforms. Given the higher single-detector duty factors, the analysis was based on threefold coincidence, to ensure the identification of any single candidate of gravitational waves with high statistical confidence. The false detection rate was as low as 1 per century. No candidates were found.

We report the result from a search for bursts of gravitational waves using data collected by the cryogenic resonant detectors EXPLORER and NAUTILUS during the year 2001, for a total measuring time of 90 days. With these data we repeated the coincidence search performed on the 1998 data (which showed a small coincidence excess) applying data analysis algorithms based on known physical characteristics of the detectors. With the 2001 data a new interesting coincidence excess is found when the detectors are favorably oriented with respect to the Galactic Disk.