Document Type
Article
Publication Date
7-29-2016
Abstract
Using circuit QED, we consider the measurement of a superconducting transmon qubit via a coupled microwave resonator. For ideally dispersive coupling, ringing up the resonator produces coherent states with frequencies matched to transmon energy states. Realistic coupling is not ideally dispersive, however, so transmon-resonator energy levels hybridize into joint eigenstate ladders of the Jaynes–Cummings type. Previous work has shown that ringing up the resonator approximately respects this ladder structure to produce a coherent state in the eigenbasis (a dressed coherent state). We numerically investigate the validity of this coherent-state approximation to find two primary deviations. First, resonator ring-up leaks small stray populations into eigenstate ladders corresponding to different transmon states. Second, within an eigenstate ladder the transmon nonlinearity shears the coherent state as it evolves. We then show that the next natural approximation for this sheared state in the eigenbasis is a dressed squeezed state and derive simple evolution equations for such states by using a hybrid phase–Fock-space description.
Recommended Citation
Khezri, M., Mlinar, E., Dressel, J., Korotkov, A.N., 2016. Measuring a transmon qubit in circuit QED: Dressed squeezed states. Physical Review A 94, 012347. doi:10.1103/PhysRevA.94.012347
Peer Reviewed
1
Copyright
American Physical Society
Comments
This article was originally published in Physical Review A, volume 94, in 2016. DOI: 10.1103/PhysRevA.94.012347