Using an operator scattering approach, we analyze the quantum dynamics of an ultrasensitive electrometer -- a Cooper pair transistor embedded in a quarter-wave microwave cavity (cCPT). While the cCPT is inherently a tunable, strongly nonlinear system affording a diverse range of functionalities, we restrict our present analysis to a necessary first investigation of its linear charge sensing capabilities, limiting to low pump powers corresponding to an average cavity photon number ≲1. Assuming realizable cCPT parameters (B. L. Brock et al., Phys. Rev. Applied, 044009), and not including noise from the subsequent amplifier chain, we predict the fundamental, photon shot noise-limited charge sensitivity to be 0.12μe/Hz when the pumped cavity has an average of one photon and the cCPT is operated close to charge degeneracy. This is to be compared with a first reported charge sensitivity value 14μe/Hz in the single-photon regime (B. L. Brock et al., arXiv:2102.05362).
@article{arxiv.2012.12313,
title = {Charge sensitivity of a cavity-embedded Cooper pair transistor limited by single-photon shot noise},
author = {S. Kanhirathingal and B. L. Brock and A. J. Rimberg and M. P. Blencowe},
journal= {arXiv preprint arXiv:2012.12313},
year = {2021}
}