Imaging non-Gaussian output fields produced by Josephson parametric amplifiers
D.M. Toyli1, A.V. Venkatramani1, S. Boutin2, A. Eddins1, A. Blais2 and I. Siddiqi1
Quantum Nanoelectronics Laboratory, UC Berkeley, US1
Departement de Physique, Universite de Sherbrooke, Canada2
In recent years, squeezed microwave states have been the focus of intense research motivated by applications in microwave quantum optics and precision qubit measurement. Despite numerous demonstrations of vacuum squeezing with superconducting devices such as the Josephson parametric amplifier (JPA), experiments have also suggested that the squeezed output field becomes non-ideal at the large signal gains required for low-noise qubit measurement. Here we describe an experimental study of JPA squeezing performance for a lumped-element design widely employed for qubit readout. In particular, we reconstruct the JPA output field through homodyne detection of the field moments and find a significant degradation in squeezing level above 10 dB of gain accompanied by increasing non-Gaussian character of the output field. Furthermore, we demonstrate a method to directly image these output fields using deconvolution techniques. Our observations are in qualitative agreement with predictions of a JPA Hamiltonian including quartic terms, suggesting that improved squeezing performance can be obtained by weakening the JPA nonlinearity. Such optimized squeezing performance enables a number of applications requiring the interaction of squeezed light and superconducting artificial atoms.
This work is supported by ARO and ONR.