A Practical Quantum-Limited Parametric Amplifier Based on the Josephson Ring Modulator.

摘要

This dissertation has addressed the problem of developing the Josephson Parametric Converter (JPC) as a practical phase-preserving microwave parametric amplifier operating at the quantum limit of added noise. The device consists of two superconducting resonators coupled through the Josephson Ring Modulator (JRM), which in essence consists of a loop of four identical Josephson tunnel junctions, threaded by an applied magnetic flux. The nonlinearity of the JRM is of the tri-linear form XYZ without spurious nonlinear terms and involving only the minimal number of modes, thus placing the JPC close to the ideal non-degenerate parametric amplifier. This pure form of the nonlinearity is confirmed here by the observation of coherent attenuation (CA), the time-reversed process of three-wave parametric amplification, with signal, idler, and pump modes in the fully nonlinear regime. The design developed in this dissertation allows fabrication of the amplifier in a single lithography step, greatly simplifying parameter adjustments from one device to the next. Measured device characteristics and amplifier performances are presented, and limitations linked to the junction energy EJ and the circuit parameters discussed. The use of these JPCs in the readout of superconducting qubits is shown to lead to almost ideal quantum measurements, as the measurement efficiency can approach the ideal value of 1.