Tiantian Huan

Trace-distance characterization of recurrent pairwise synchronization in cavity-coupled superconducting qubits

  1. Tiantian Huan
We theoretically investigate recurrent pairwise synchronization in three super?conducting qubits coupled to a common single-mode microwave cavity. The qubits interact indirectly through
the cavity field and are driven by a coher?ent microwave field. We obtain the coherent dynamics in the dressed-state basis and quantify pairwise synchronization by the trace distance between reduced single-qubit density matrices. The trace-distance dynamics exhibit oscillatory wave-packet structures, with low-trace-distance regions identifying finite syn?chronization windows. An envelope-threshold procedure is introduced to extract the representative duration of these windows. By varying the middle-qubit coupling strength and the relative coupling ratio of the outer qubits, we con?struct a parameter-dependent map of the synchronization-window duration. The duration decreases rapidly with increasing relative outer-qubit coupling and becomes weakly dependent on the middle-qubit coupling in the stronger-coupling regime. These results provide a reduced-state-based characterization of coherent collective dynamics in multiqubit circuit-QED systems.
arxiv pdf

Ramsey-biased spectroscopy of superconducting qubits under dispersion

  1. Yan Zhang,
  2. Tiantian Huan,
  3. Ri-gui Zhou,
  4. and Hou Ian
We proposed a spectroscopic method that extends Ramsey’s atomic spectroscopy to detect the transition frequency of a qubit fabricated on a superconducting circuit. The method
uses a multi-interval train of qubit biases to implement an alternate resonant and dispersive couplings to an incident probe field. The consequent absorption spectrum of the qubit has a narrower linewidth at its transition frequency than that obtained from constantly biasing the qubit to resonance while the middle dispersive evolution incurs only a negligible shift in detected frequency. Modeling on transmon qubits, we find that the linewidth reduction reaches 23% and Ramsey fringes are simultaneously suppressed at extreme duration ratio of dispersion over resonance for a double-resonance scheme. If the scheme is augmented by an extra resonance segment, a further 37% reduction can be achieved.
arxiv pdf