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Ultracold quantum-gas mixtures of fermionic atoms with resonant control of interactions offer a unique test-bed to explore few- and many-body quantum states with unconventional properties. The emergence of such strongly correlated systems, as for instance symmetry-broken superfluids, is usually accompanied by hydrodynamic collective behavior. Thus, experimental progress in this field naturally requires a deep understanding of hydrodynamic regimes. Here, we report on experiments employing a tunable Fermi-Fermi mixture of $^{161}$Dy and $^{40}$K near quantum degeneracy. We investigate the full spectrum of dipole modes across a Feshbach resonance and characterize the crossover from collisionless to deep hydrodynamic behavior in measurements of frequencies and damping rates. We compare our results with a theoretical model that considers the motion of the mass centers of the two species and we identify the contributions of friction and mean-field interaction. We show that one oscillating mode exists over the whole range of interactions, exhibiting striking changes of frequency and damping in the deep hydrodynamic regime. We observe the second oscillating mode to split into two purely exponential damping modes. One of these exponential modes shows very fast damping, faster than any other relevant timescale, and is largely insensitive against experimental imperfections. It provides an accurate measure for the interspecies drag effect, which generalizes the concept of spin drag explored in other experiments. We characterize the interspecies drag locally in terms of a microscopic friction coefficient and we discuss its unitarity-limited universal behavior on top of the resonance., Comment: 20 pages, 11 figures

We report on the observation of a conspicuous loss in an ultracold mixture of $^{7}$Li and $^{88}$Sr atoms confined in a far-off-resonance optical dipole trap. We attribute the trap loss to the three-body inelastic Li-Sr-Sr collision and extract the corresponding three-body recombination coefficient $K_3$ at $T\sim 18.5,45,70,600$ $\mu K$. The measured three-body recombination coefficient is about two to three orders of magnitude larger than the typical values convenient for realizing quantum degenerate gases. It also indicates a potentially large $s$-wave scattering length between the bosonic $^{7}$Li and $^{88}$Sr atoms, and essentially rules out the prospect of realizing $^7$Li and $^{88}$Sr mixtures of high phase space density., Comment: 6 pages

We report on the preparation of a pure ultracold sample of bosonic DyK Feshbach molecules, which are composed of the fermionic isotopes 161Dy and 40K. Employing a magnetic sweep across a resonance located near 7.3 G, we produce up to 5000 molecules at a temperature of about 50 nK. For purification from the remaining atoms, we apply a Stern-Gerlach technique based on magnetic levitation of the molecules in a very weak optical dipole trap. With the trapped molecules we finally reach a high phase-space density of about 0.1. We measure the magnetic field dependence of the molecular binding energy and the magnetic moment, refining our knowledge of the resonance parameters. We also demonstrate a peculiar anisotropic expansion effect observed when the molecules are released from the trap and expand freely in the magnetic levitation field. Moreover, we identify an important lifetime limitation that is imposed by the 1064-nm infrared trap light itself and not by inelastic collisions. The light-induced decay rate is found to be proportional to the trap light intensity and the closed-channel fraction of the Feshbach molecule. These observations suggest a one-photon coupling to electronically excited states to limit the lifetime and point to the prospect of loss suppression by optimizing the wavelength of the trapping light. Our results represent important insights and experimental steps on the way to achieve quantum-degenerate samples of DyK molecules and novel superfluids based on mass-imbalanced fermion mixtures.

We report on the observation of Feshbach resonances at low magnetic field strength (below 10 G) in the Fermi-Fermi mixture of $^{161}$Dy and $^{40}$K. We characterize five resonances by measurements of interspecies thermalization rates and molecular binding energies. As a case of particular interest for applications, we consider a resonance near 7.29 G, which combines accurate magnetic tunability and access to the universal regime of interactions with experimental simplicity. We show that lifetimes of a few 100 ms can be achieved for the optically trapped, resonantly interacting mixture. We also demonstrate the hydrodynamic expansion of the mixture in the strongly interacting regime and the formation of DyK Feshbach molecules. Our work opens up new experimental possibilities in view of mass-imbalanced superfluids and related phenomena.

We report on the attainment of a degenerate Fermi gas of $\rm^{6}Li$ in contact with a Bose-Einstein condensate (BEC) of $^{84}$Sr. A degeneracy of $T/T_F=0.33(3)$ is observed with $1.6\times10^5$ $^{6}$Li atoms in the two lowest energy hyperfine states together with an almost pure BEC of $3.1\times10^5$ $^{84}$Sr atoms. The elastic s-wave scattering length between $^6$Li and $^{84}$Sr is estimated to be $|a_{\rm^{6}Li-\rm^{84}Sr}|=(7.1_{-1.7}^{+2.6})a_0$ ($a_0$ being the Bohr radius) from measured interspecies thermalization rates in an optical dipole trap., Comment: 8 pages, 6 figures

The total ionizing radiation (TID) response of commercial NPN silicon germanium hetero-junction bipolar transistors (SiGe HBTs) produced domestic were investigated under the dose rate of 800mGy(Si)/s and 1.3mGy(Si)/s with Co-60 gamma irradiation source, respectively. The changes of the transistor parameter such as Gummel characteristics, excess base current before and after irradiation are investigated. The results of the experiments shows that for the KT1151, the radiation damage have slightly difference under the different dose rate after the prolonged annealing, shows an time dependent effect(TDE). But for the KT9041, the degradations of low dose rate irradiation are more higher than the high dose rate, demonstrate that there have potential enhanced low dose rate sensitive(ELDRS) effect exist on KT9041. The underlying physical mechanisms of the different dose rates response induced by the gamma ray are discussed.