Hou Ian

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

Pulse-qubit interaction in a superconducting circuit under frictively dissipative environment

  1. Yibo Gao,
  2. Shijie Jin,
  3. Yan Zhang,
  4. and Hou Ian
Microwave pulses are used ubiquitously to control and measure qubits fabricated on superconducting circuits. Due to continual environmental coupling, the qubits undergo decoherence
both when it is free and during its interaction with the microwave pulse. As quantum logic gates are executed through pulse-qubit interaction, we study theoretically the decoherence-induced effects during the interaction, especially the variations of the pulse, under a dissipative environment with linear spectral distribution. We find that a transmissible pulse of finite width adopts an asymmetric multi-hump shape, due to the imbalanced pumping and emitting rates of the qubit during inversion when the environment is present. The pulse shape reduces to a solitonic pulse at vanishing dissipation and a pulse train at strong dissipation. We give detailed analysis of the environmental origin from both the perspectives of envelope and phase of the propagating pulse.
arxiv pdf