Nonlinear charge sensing with the cavity-embedded Cooper pair transistor*

The cavity-embedded Cooper pair transistor (cCPT) has been shown to be an extremely sensitive linear charge detector when operating at single-photon levels [1]. We report on the operation of the cCPT as a nonlinear charge sensor. Using the inherent Kerr nonlinearity, we demonstrate a Josephson bifurcation amplifier [2] inspired dispersive charge sensing technique by driving the cCPT at a detuning close to a bifurcation edge. This is implemented using ~100s of photons, still several orders of magnitude lower than what is used for state-of-the-art charge detection techniques using radio frequency single electron transistors. We also explore a second nonlinear detection technique in which we parametrically pump the cCPT using a time-varying flux. Flux pumping the cCPT at a detuning on the edge of the parametric oscillation threshold makes the amplitude of oscillations sensitive to the charge environment.

 

[1] B. L. Brock et. al,  arXiv:2102.05362 (2021)

[2] R. Vijay, M. H. Devoret, and I. Siddiqi , Review of Scientific Instruments 80, 111101 (2009)