Displaced Frame Approach for Simulating High-Power Dispersive Readout

Dispersive readout is a ubiquitous method in the sense that the readout scheme can be applied to any type of superconducting qubits. To make the readout time shorter in the dispersive readout, one possible approach is using high-power-input light. The high-power input light increases signals from a cavity interacting with a qubit. However, the working principle of the dispersive readout is based on the perturbation theory, and the spectrum of the transmon, one of the standard implementations of qubit, is unbounded. Consequently, back actions from high-power input are nontrivial, and some numerical simulations are required to investigate these effects. The numerical simulations are heavy tasks since high-power light induces a large-amplitude coherent state that requires many Fock states for its representation. To perform the simulations efficiently, we propose an approach to simulate the dynamics in a frame where the amplitude of the coherent state almost vanishes [1]. The proposed method requires fewer Fock states compared to the same simulation in the drive frame. The proposed method enables one to access the high-power dispersive readout in the two-level system and the transmon with moderate numerical resources.

[1] S. Goto and K. Koshino, Phys. Rev. A 108, 033722 (2023)