Manuel Castellanos-Beltran

Quantum state tomography of an itinerant squeezed microwave field.

We perform state tomography of an itinerant squeezed state of the microwave field prepared by a Josephson parametric amplifier (JPA). We use a second JPA as a preamplifier to improve the quantum efficiency of the field quadrature measurement from 2% to 36%±4%. Without correcting for the detection inefficiency we observe a minimum quadrature variance which is 68(-7)(+9)% of the variance of the vacuum. We reconstruct the states density matrix by a maximum likelihood method and infer that the squeezed state has a minimum variance less than 40% of the vacuum, with uncertainty mostly caused by calibration systematics.

Evaluation of a Microwave SQUID Multiplexer Prototype

As large arrays of ultrasensitive cryogenic detectors of radiant energy are developed, multiplexing schemes are required to manage system complexity. Any such scheme must also meet stringent sensitivity, bandwidth, dynamic range and power dissipation specifications. We describe preliminary tests of a microwave frequency-division multiplexed readout of SQUID amplifiers. From these initial tests we estimated the number of SQUIDs that can be multiplexed with this scheme and the sensitivity and bandwidth of each SQUID amplifier.

Bandwidth and Dynamic Range of a Widely Tunable Josephson Parametric Amplifier

We characterize the signal bandwidth and dynamic range of a recently developed type of Josephson parametric amplifier. These amplifiers consist of a series array of SQUIDs embedded in a microwave cavity. They are narrow band, only amplifying signals close to the cavitys resonance frequency, but the cavitys resonance frequency, and hence the amplified band, can be widely tuned. For a particular realization of these amplifiers we measure how the signal bandwidth depends on amplifiers gain. We find that the amplitude gain times signal bandwidth is approximately the linewidth of the cavity. In addition we measure the amplifiers dynamic range and saturation power.