Strong environmental coupling in a Josephson parametric amplifier
  We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behaviour using the "pumpistor" model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over gain profiles through changes in the environment impedance at a given frequency. With strong coupling to a suitable external impedance we observe a significant increase in dynamic range, and large amplification bandwidth up to 700 MHz giving near quantum-limited performance. 
Josh Mutus, Ted White, Rami Barends, Yu Chen, Zijun Chen, Ben Chiaro,   Andrew Dunsworth, Evan Jeffrey, Julian Kelly, Anthon...
cond-mat.supr-con