Yueh-Nan Chen

Mitigation of Measurement-Induced State Transitions via a Fast-Load and Fast-Clear Readout

  1. Wei-En Lin,
  2. Li-Chieh Hsiao,
  3. Chen-Hsun Ma,
  4. Erh-Hsiang Yeh,
  5. Wei-Lun Peng,
  6. Hsi-Sheng Goan,
  7. Cen-Shawn Wu,
  8. Yueh-Nan Chen,
  9. Yung-Fu Chen,
  10. Chung-Ting Ke,
  11. and Chii-Dong Chen
High-fidelity and rapid qubit readout is essential for superconducting quantum processors, typically realized through the quantum non-demolition (QND) dispersive interaction within
a qubit-resonator architecture. However, the achievable readout speed and fidelity are fundamentally limited by measurement-induced state transitions (MIST). For a transmon qubit, MIST is highly sensitive to the offset charge ng due to the charge dispersion of its higher-lying energy levels. In this work, we systematically investigate ng-dependent MIST dynamics governed by the diabaticity and symmetry of pulse shaping within a charge-sensitive transmon architecture. We engineer fast-load and fast-clear pulses that effectively suppress resonator photon overshoots, thereby demonstrating a highly practical strategy to mitigate MIST without requiring complex waveforms or real-time feedback. Utilizing active gate-voltage control and rapid feedback, the measurement-induced transition probability is precisely mapped against ng and the steady-state resonator photon number, exhibiting strong agreement with numerical Floquet branch analysis. Ultimately, we evaluate the ng-averaged total error probabilities for both readout and post-readout stages, verifying that a straightforward three-step pulse scheme consistently minimizes overall readout errors. Within the framework of large-scale superconducting quantum processors, this practical, hardware-free approach inherently offers a better trade-off between the readout signal-to-noise ratio and QND preservation.
arxiv pdf

Causality test on Cherenkov effect in circuit QED

  1. Jhen-Dong Lin,
  2. and Yueh-Nan Chen
We investigate the Cherenkov radiation triggered by qubit acceleration simulated by superconducting circuit. By analyzing the radiation probability, we confirm the existence of Cherenkov
speed threshold, implying that simulating superluminal qubit motion is possible for such a scenario. A question immediately arises: Is such motion compatible with the causality principle? To address the question, we perform a causality test on the simulating system based on the recently developed notion of temporal quantum correlations, pseudo-density matrix and temporal quantum steering. The results suggest that single-mode approximation breaks down even when the system is restricted in weak coupling regime.
arxiv pdf

Probing higher-order transitions through scattering of microwave photons in the ultrastrong-coupling regime of circuit QED

  1. Guan-Ting Chen,
  2. Po-Chen Kuo,
  3. Huan-Yu Ku,
  4. Guang-Yin Chen,
  5. and Yueh-Nan Chen
Higher-order transitions can occur in the ultrastrong-coupling regime of circuit QED through virtual processes governed by the counter-rotating interactions. We propose a feasible way
to probe higher-order transitions through the scattering of propagating microwave photons incident on the hybrid qubit-cavity system. The lineshapes in the scattering spectra can indicate the coherent interaction between the qubits and the cavity, and the higher-order transitions can be identified in the population spectra. We further find that if the coupling strengths between the two qubits and the cavity are tuned to be asymmetric, the dark antisymmetric state with the Fano-lineshape can also be detected from the variations in the scattering spectra.
arxiv pdf