A tunable parametric amplifier based on a SQUID array resonator with nearly quantum-limited sensitivity

Recently, there has been an increasing number of compelling applications for quantum-limited amplifiers at microwaves frequencies. These include the readout of superconducting qubits and ultrasensitive measurements of the motion of nanomechanical beams. Although quantum-limited microwave amplifiers have already been demonstrated, they have suffered from both limited bandwidth and dynamic range. We create a Josephson parametric amplifier from a transmission line resonator whose inner conductor is made from a series SQUID array. By changing the magnetic flux through the SQUID loops, we are able to adjust the circuit's resonance frequency and, consequently, the center of the amplified band over an octave (4-8 GHz). This tunability circumvents some of the problems related to a limited bandwidth. We will discuss recent results that include demonstration of large gain (30 dB), nearly quantum-limited sensitivity and noise squeezing.