Widely tunable, non-degenerate three-wave mixing microwave device   operating near the quantum limit
  We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions shunted by a cross of four linear inductances. The phase configuration of the ring remains unique over a wide range of magnetic fluxes threading the loop. It is thus possible to vary the inductance of the ring with flux while retaining a strong, dissipation-free, and noiseless non-linearity. The device has been operated in amplifier mode and its noise performance has been evaluated by using the noise spectrum emitted by a voltage biased tunnel junction at finite frequency as a test signal. The unprecedented accuracy with which the crossover between zero-point-fluctuations and shot noise has been measured provides an upper-bound for the noise and dissipation intrinsic to the device. 
Nicolas Roch, Emmanuel Flurin, Fran\c{c}ois Nguyen, Pascal Morfin,   Philippe Campagne-Ibarcq, Michel H. Devoret and Benjami...
cond-mat.mes-hall physics.ins-det quant-ph