We analyze the quantum dynamics of a superconducting cavity coupled to a voltage-biased Josephson junction. The cavity is strongly excited at resonances where the voltage energy lost by a Cooper pair traversing the circuit is a multiple of the cavity photon energy. We find that the resonances are accompanied by substantial squeezing of the quantum fluctuations of the cavity over a broad range of parameters and are able to identify regimes where the fluctuations in the system take on universal values.

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We have studied the effect of tensile strain on the superconductivity in FeSe films. 50 nm, 100 nm, and 200 nm FeSe films were grown on MgO, SrTiO$_3$, and LaAlO$_3$ substrates by using a pulsed laser deposition technique. X-ray diffraction analysis showed that the tetragonal phase is dominant in all of our FeSe films. The 50 nm FeSe films on MgO and SrTiO$_3$ are under tensile strain, while the 50 nm FeSe film on LaAlO$_3$ and the other thick FeSe films are unstrained. Superconducting transitions have been observed in unstrained FeSe films with T$_{onset}$ $\approx$ 8 K, which is close to the bulk value. However, no sign of superconductivity has been observed in FeSe films under tensile strain down to 5 K. There is evidence to show that tensile strain suppresses superconductivity in FeSe films

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