Flexible Readout and Unconditional Reset for Superconducting Multi-Qubit Processors with Tunable Purcell Filters

  1. Yong-Xi Xiao,
  2. Da'er Feng,
  3. Xu-Yang Gu,
  4. Gui-Han Liang,
  5. Ming-Chuan Wang,
  6. Zheng-Yu Peng,
  7. Bing-Jie Chen,
  8. Yu Yan,
  9. Zheng-Yang Mei,
  10. Si-Lu Zhao,
  11. Yi-Zhou Bu,
  12. Cheng-Lin Deng,
  13. Xiaohui Song,
  14. Dongning Zheng,
  15. Yu-Xiang Zhang,
  16. Yun-Hao Shi,
  17. Zhongcheng Xiang,
  18. Kai Xu,
  19. and Heng Fan
Qubit readout and reset are critical components for the practical realization of quantum computing systems, as outlined by the DiVincenzo criteria. Here, we present a scalable architecture
employing frequency-tunable nonlinear Purcell filters designed specifically for superconducting qubits. This architecture enables flexible readout and unconditional reset functionalities. Our readout protocol dynamically adjusts the effective linewidth of the readout resonator through a tunable filter, optimizing the signal-to-noise ratio during measurement while suppressing photon noise during idle periods. Achieving a readout fidelity of 99.3% without using Josephson parametric amplifiers or traveling-wave parametric amplifiers, even with a small dispersive shift, demonstrates its effectiveness. For reset operations, our protocol utilizes the tunable coupler adjacent to the target qubit as an intermediary to channel qubit excitations into the Purcell filter, enabling rapid dissipation. We demonstrate unconditional reset of both leakage-induced |2⟩ and |1⟩ states within 200 ns (error rate ≤1%), and reset of the |1⟩ state alone in just 75 ns. Repeated reset cycles (≤600 ns) further reduce the error rate below 0.1%. Furthermore, the filter suppresses both photon noise and the Purcell effect, thereby reducing qubit decoherence. This scalable Purcell filter architecture shows exceptional performance in qubit readout, reset, and protection, marking it as a promising hardware component for advancing fault-tolerant quantum computing systems.

A Charge-Noise Insensitive Chiral Photonic Interface for Waveguide Circuit QED

  1. Yu-Xiang Zhang,
  2. Carles R. i Carceller,
  3. Morten Kjaergaard,
  4. and Anders S. Sørensen
A chiral photonic interface is a quantum system that has different probabilities for emitting photons to the left and right. An on-chip compatible chiral interface is attractive for
both fundamental studies of light-matter interactions and applications to quantum information processing. We propose such a chiral interface based on superconducting circuits, which has wide bandwidth, rich tunability, and high tolerance to fabrication variations. The proposed interface consists of a core that uses Cooper-pair-boxes (CPBs) to break time-reversal symmetry, and two superconducting transmons which connect the core to a waveguide in the manner reminiscent of a „giant atom“. The transmons form a state decoupled from the core, akin to dark state of atomic physics, rendering the whole interface insensitive to the CPB charge noise. The proposed interface can be extended to realize a broadband fully passive on-chip circulator for microwave photons.