Multi-level selection rules of a Tunable Coupling Qubit*

We study the level structure of a tunable coupling qubit (TCQ) [Ref. 1, 2] by microwave spectroscopy in superconducting circuit architecture. Based on the two independently tunable SQUID loops, the multi-level structure of a TCQ can be tuned in-situ. We demonstrated that a TCQ is a charge qubit while providing tunable selection rule. Accompanied with the mode-tunability in coplanar waveguide design, V-type, lambda-type and many other structures can be achieved in a TCQ-based architecture. TCQs have potential for the application of microwave quantum optics.

[1] S. J. Srinivasan et al., Phys. Rev. Lett. 106, 083601 (2011)
[2] J. M. Gambetta et al., Phys. Rev. Lett. 106, 030502 (2011)