Erh-Hsiang Yeh

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

Suppression of Quasiparticle Poisoning to 10−11 Levels in Superconducting Qubits via Infrared Shielding

  1. Wei-En Lin,
  2. Chen-Hsun Ma,
  3. Erh-Hsiang Yeh,
  4. Wei-Lun Peng,
  5. Yu-Sen Wei,
  6. Hsi-Sheng Goan,
  7. Cen-Shawn Wu,
  8. Chung-Ting Ke,
  9. Yung-Fu Chen,
  10. and Chii-Dong Chen
Quasiparticle poisoning bottlenecks superconducting qubits, limiting coherence and the scalability of quantum processors. In this work, we systematically investigate quasiparticle poisoning
in superconducting qubits under three infrared (IR) shielding configurations, ranging from a dedicated multi-layer design to a simplified implementation. By measuring quasiparticle-induced parity switching, we demonstrate a suppression of the switching rate by over four orders of magnitude via the implementation of improved shielding. In the best configuration, the rate decreases over time following cooldown and reaches 0.069Hz on day 34, corresponding to an anticipated quasiparticle density per Cooper pair of 1.88×10−11. To our knowledge, this represents the lowest quasiparticle density reported in the literature to date. The remaining quasiparticle population is likely dominated by sporadic phonon bursts stemming from mechanical stress release in the on-chip films, as well as from the surrounding environment. The effective qubit temperature follows the phonon bath down to 17mK, enabling initialization errors of ∼0.01% for 3GHz qubits. These results demonstrate that proper IR shielding and thermalization are essential for suppressing quasiparticle poisoning and enabling high-coherence, scalable superconducting qubit systems.
arxiv pdf