Advanced Concepts in Josephson Junction Reflection Amplifiers
  Low-noise amplification atmicrowave frequencies has become increasingly important for the research related to superconducting qubits and nanoelectromechanical systems. The fundamental limit of added noise by a phase-preserving amplifier is the standard quantum limit, often expressed as noise temperature $T_{q} = \hbar {\omega}/2k_{B}$. Towards the goal of the quantum limit, we have developed an amplifier based on intrinsic negative resistance of a selectively damped Josephson junction. Here we present measurement results on previously proposed wide-band microwave amplification and discuss the challenges for improvements on the existing designs. We have also studied flux-pumped metamaterial-based parametric amplifiers, whose operating frequency can be widely tuned by external DC-flux, and demonstrate operation at $2\omega$ pumping, in contrast to the typical metamaterial amplifiers pumped via signal lines at $\omega$. 
Pasi L\"ahteenm\"aki, Visa Vesterinen, Juha Hassel, G. S. Paraoanu,   Heikki Sepp\"a, and Pertti Hakonen
cond-mat.mes-hall quant-ph