Interferometric Transmon Readout with Two-Mode Squeezed Light, Part 1*

Quantum fluctuations set an inherent limit on the signal-to-noise ratio (SNR) of qubit readout. This limitation can be circumvented, however, by the use of squeezed inputs, for instance a two mode squeezed state flowing into a phase-preserving amplifier [Liu, et al., PRA (2022)]]. In this work, we explore the benefits of a two-mode squeezed light interferometer-based readout scheme. Our set up involves two single-mode, high-saturation power Josephson parametric amplifiers (JPAs): one placed before the qubit cavity system, which feeds our qubit cavity system squeezed vacuum, and one placed after, which amplifies the signal as in a normal readout chain. This interferometer consists of not two independent transmission paths, but the upper and lower sidebands of the amplifiers. Having the cavity interact only with the upper sideband, for instance, allows for noise reduction and enhancement of the SNR of our readout. In the first part of this talk, we present the experiment design and initial results of our interferometric readout, focusing on losses in the system and careful characterization of the squeezed light in our interferometer, as well as how the high saturation power of our amplifiers allows us to optimize the system to demonstrate high degrees of one- and two-mode squeezing.