Superconducting Circuit QED System Interacting with Quantum Spins

• Speaker: Choi, Mahn-Soo (Korea University)

Superconducting circuit QED systems provides a wide range of scientific platforms from quantum computer to accurate quantum sensing of elementary charge or spin. In this talk, we first examine the exotic quantum states of the circuit QED systems in the ultra-strong coupling limit. They can simulate the Majorana bound state and exhibit photon localization-delocalization double transitions [1,2]. Next, we demonstrate how the frozen charge state at the Kondo resonance can be directly probed using the circuit QED architecture [3]. A quantum dot is coupled to a high finesse microwave cavity to measure, with an unprecedented sensitivity, the dot electronic compressibility. It is illustrated that the Kondo resonance, visible in transport measurements, is ‘transparent’ to microwave photons trapped in the high finesse cavity. Finally, we discuss unusual physical properties of a circuit QED system in which the Transmon qubit involves a quantum spin. The 0-π transition resulting from the competition of superconductivity and Kondo effect [4] gives rise to rich characteristics of the circuit QED systems from negative supercurrent to anharmonic-doubling effect [5].

References

1. M.-J. Hwang and Mahn-Soo Choi, Phys. Rev. B 87, 125404 (2013).
2. M.-J. Hwang, M. Kim, and Mahn-Soo Choi, Phys. Rev. Lett. 116, 153601 (2016).
3. M. M. Desjardins et al., Nature 545, 71 (2017).
4. Mahn-Soo Choi, M. Lee, K. Kang, W. Belzig, Phys. Rev. B 70, 020502 (2004); Phys. Rev. Lett. 94, 229701 (2005).
5. A recent experiment by P. J. Leek (private conversation).