Single-Shot Readout of Fluxonium Qubits.*

We discuss the possibility of the single-shot readout of fluxonium superconducting qubits [1] based on the preparation of the "bright" and "dark" cavity states. With a proper choice of parameters, the dispersive shift of the cavity (the distance between its dressed and bare resonance frequencies) for the qubit 0 state can be made much smaller than this shift for the qubit 1 state. Thus, the cavity nonlinearity can be made much weaker for the qubit 0 than for the qubit 1 states. This has a potential to improve two types of single-shot qubit readout schemes that are used in the transmon readout, when the cavity nonlinearity is comparable for the two transmon states. First, for the readout based on microwave photon counters [2], one can achieve a higher cavity occupation in its bright state. Second, for the high-power readout [3], the onset of the bright transmission for one of the qubit states can occur at lower power.

[1] L. B. Nguyen, et. al., arXiv:1810.11006 (2018).
[2] A. Opremcak, et. al., Science 361, 1239 (2018).
[3] M. D. Reed, et. al., Phys. Rev. Lett. 105, 173601 (2010).