Feng-Ming Liu

99.9%-fidelity in measuring a superconducting qubit

  1. Can Wang,
  2. Feng-Ming Liu,
  3. He Chen,
  4. Yi-Fei Du,
  5. Chong Ying,
  6. Jian-Wen Wang,
  7. Yong-Heng Huo,
  8. Cheng-Zhi Peng,
  9. Xiaobo Zhu,
  10. Ming-Cheng Chen,
  11. Chao-Yang Lu,
  12. and Jian-Wei Pan
Despite the significant progress in superconducting quantum computation over the past years, quantum state measurement still lags nearly an order of magnitude behind quantum gate operations
in speed and fidelity. The main challenge is that the strong coupling and readout signal used to probe the quantum state may also introduce additional channels which may cause qubit state transitions. Here, we design a novel architecture to implement the long-sought longitudinal interaction scheme between qubits and resonators. This architecture not only provides genuine longitudinal interaction by eliminating residual transversal couplings, but also introduces proper nonlinearity to the resonator that can further minimize decay error and measurement-induced excitation error. Our experimental results demonstrate a measurement fidelity of 99.8% in 202 ns without the need for any first-stage amplification. After subtracting the residual preparation errors, the pure measurement fidelity is above 99.9%. Our scheme is compatible with the multiplexing readout scheme and can be used for quantum error correction.
arxiv pdf

Quantum Design for Advanced Qubits

  1. Feng-Ming Liu,
  2. Ming-Cheng Chen,
  3. Can Wang,
  4. Shao-Wei Li,
  5. Zhong-Xia Shang,
  6. Chong Ying,
  7. Jian-Wen Wang,
  8. Cheng-Zhi Peng,
  9. Xiaobo Zhu,
  10. Chao-Yang Lu,
  11. and Jian-Wei Pan
Simulations of high-complexity quantum systems, which are intractable for classical computers, can be efficiently done with quantum computers. Similarly, the increasingly complex quantum
electronic circuits themselves will also need efficient simulations on quantum computers, which in turn will be important in quantum-aided design for next-generation quantum processors. Here, we implement variational quantum eigensolvers to simulate a Josephson-junction-array quantum circuit, which leads to the discovery of a new type of high-performance qubit, plasonium. We fabricate this new qubit and demonstrate that it exhibits not only long coherence time and high gate fidelity, but also a shrinking physical size and larger anharmonicity than the transmon, which can offer a number of advantages for scaling up multi-qubit devices. Our work opens the way to designing advanced quantum processors using existing quantum computing resources.
arxiv pdf