Abstract
We measure the dispersive energy-level shift of an resonator magnetically coupled to a superconducting qubit, which clearly shows that our system operates in the ultrastrong coupling regime. The large mutual kinetic inductance provides a coupling energy of , requiring the addition of counter-rotating-wave terms in the description of the Jaynes-Cummings model. We find a 50 MHz Bloch-Siegert shift when the qubit is in its symmetry point, fully consistent with our analytical model.
- Received 10 May 2010
DOI:https://doi.org/10.1103/PhysRevLett.105.237001
© 2010 The American Physical Society