Cold samples of calcium atoms are prepared in the metastable 3 P1 state inside an optical cavity resonant with the narrow band (375 Hz) 1 S0 → 3 P1 intercombination line at 657 nm. We observe superradiant emission of hyperbolic secant shaped pulses into the cavity with an intensity proportional to the square of the atom number, a duration much shorter than the natural lifetime of the 3 P1 state, and a delay time fluctuating from shot to shot in excellent agreement with theoretical predictions. Our incoherent pumping scheme to produce inversion on the 1 S0 → 3 P1 transition should be extendable to allow for continuous wave laser operation. PACS numbers: 42.50.Nn, 06.30.Ft, 37.10.Jk, 37.30.+i Conventional lasers typically operate in the so-called good cavity limit, where the resonance bandwidth of the feedback cavity is by far more narrow than the spectral width of the gain profile. The achievable emission bandwidth is presently approaching fundamental limitations by intrinsic thermal fluctuations of the cavity materials [1-3], which is one of the obstacles for further improvements of the precision of atomic clocks [4]. An alternative approach to circumvent these limitations relies on the use of an ultra-narrow bandwidth gain material, as provided by two-electron atoms like calcium or strontium, in combination with a comparatively large cavity bandwidth. In this so-called bad cavity regime, the average intra-cavity photon number can be kept small and even well below unity such that the intra-cavity field cannot establish coherence, as in the good cavity regime. Here, it is rather the long-lived atomic polarization providing the phase memory necessary to form coherence by superradiant emission, with the result of a sensitivity to technical noise sources reduced by many orders of magnitude. Bad cavity lasers, also referred to as superradiant lasers, are a subject of ongoing theoretical [5-8] and experimental [9,10] research. In the recent past, superradiant lasing has undergone a renaissance in connection with the use of ultranarrow band intercombination lines of alkaline-earth atoms [8,[11][12][13][14], which could provide extremely low emission bandwidths in the sub-millihertz regime.Superradiant emission of an inverted system in free space has been studied since the fifties [15][16][17][18][19][20][21][22] followed by first observations in the optical domain in the seventies [23][24][25]. More recently, a new line of research has been concerned with the collective light scattering by dense ultra-cold samples of atoms in free space as well as inside optical cavities [26][27][28][29]. On a macroscopic level, a completely inverted system represents an unstable equilibrium. Its decay is triggered by microscopic quantum fluctuations, which translate into macroscopic shot to shot delay time fluctuations of classical superradiant light pulses. This phenomenon has been theoretically studied [22,30] but a quantitative comparison with experiments is yet missing. In this article we report the first pulsed superradiant las...

We study binary collisions of metastable calcium atoms ($^{40}$Ca) in an optical dipole trap. Collisions between $^{3}$P$_{0}$-atoms and between $^{3}$P$_{0}$ and $^{1}$S$_{0}$-atoms are considered. In the former case, the elastic and inelastic collision parameters are found to be $5.4\times 10^{-11}\,\mathrm{cm}^{3}\mathrm{s}^{-1}$ and $3.6\times 10^{-11}\,\mathrm{cm}^{3}\mathrm{s}^{-1}$, respectively. A fraction of the collisions between $^{3}$P$_{0}$-atoms is found to produce cold trapped atoms in the singlet $^{1}$S$_{0}$ state, suggesting that the internal energy for these collisions is dissipated by radiation. For collisions between $^{3}$P$_{0}$ and $^{1}$S$_{0}$-atoms we find a two-body loss parameter of $8.5\times 10^{-11}\,\mathrm{cm}^{3}\mathrm{s}^{-1}$. Our observations show that metastable calcium samples in the $^{3}$P$_{0}$-state are not stable at high densities, as for example required in quantum computing or many-body quantum simulation schemes.Comment: 5 pages, 7 Figure

Eisosomes are plasma-membrane-associated protein complexes of fungi and algae involved in various cellular processes. The eisosome composition of the budding yeast is well described, but there is a limited number of studies only about eisosomes in filamentous fungi. In our study, we examined the Neurospora crassa LSP-1 protein (NcLSP1). By complementing a Saccharomyces cerevisiae Δpil1 mutant strain with nclsp1, we show the functional homology of the NcLSP1 to yeast PIL1 rather than to yeast LSP1 and hereby confirm that the NcLSP1 is an eisosomal core protein and suitable eisosomal marker. The subsequent cloning and expression of the nclsp1::trfp reporter gene construct in N. crassa allowed for a systematical investigation of the characteristics of eisosome formation and distribution in different developmental stages. In N. crassa, the hyphae germinating from sexual and asexual spores are morphologically identical and have been historically recognized as the same type of cells. Here, we demonstrate the structural differences on the cellular level between the hyphae germinating from sexual and asexual spores.