Conditional coherent control with superconducting artificial atoms

  1. Chang-Kang Hu,
  2. Jiahao Yuan,
  3. Bruno A. Veloso,
  4. Jiawei Qiu,
  5. Yuxuan Zhou,
  6. Libo Zhang,
  7. Ji Chu,
  8. Orkesh Nurbolat,
  9. Ling Hu,
  10. Jian Li,
  11. Yuan Xu,
  12. Youpeng Zhong,
  13. Song Liu,
  14. Fei Yan,
  15. Dian Tan,
  16. R. Bachelard,
  17. Alan C. Santos,
  18. C. J. Villas-Boas,
  19. and Dapeng Yu
Controlling the flow of quantum information is a fundamental task for quantum computers, which is unpractical to realize on classical devices. Coherent devices which can process quantum
states are thus required to route the quantum states yielding the information. In this paper we demonstrate experimentally the smallest quantum transistor for superconducting processors, composed of collector and emitter qubits, and the coupler. The interaction strength between the collector and emitter is controlled by tuning the frequency and the state of the gate qubit, effectively implementing a quantum switch. From the truth-table measurement (open-gate fidelity 93.38%, closed-gate fidelity 98.77%), we verify the high performance of the quantum transistor. We also show that taking into account the third energy level of the qubits is critical to achieving a high-fidelity transistor. The presented device has a strong potential for quantum information processes in superconducting platforms.

Optimal charging of a superconducting quantum battery

  1. Chang-Kang Hu,
  2. Jiawei Qiu,
  3. Paulo J. P. Souza,
  4. Jiahao Yuan,
  5. Yuxuan Zhou,
  6. Libo Zhang,
  7. Ji Chu,
  8. Xianchuang Pan,
  9. Ling Hu,
  10. Jian Li,
  11. Yuan Xu,
  12. Youpeng Zhong,
  13. Song Liu,
  14. Fei Yan,
  15. Dian Tan,
  16. R. Bachelard,
  17. C. J. Villas-Boas,
  18. Alan C. Santos,
  19. and Dapeng Yu
Quantum batteries are miniature energy storage devices and play a very important role in quantum thermodynamics. In recent years, quantum batteries have been extensively studied, but
limited in theoretical level. Here we report the experimental realization of a quantum battery based on superconducting qubits. Our model explores dark and bright states to achieve stable and powerful charging processes, respectively. Our scheme makes use of the quantum adiabatic brachistochrone, which allows us to speed up the {battery ergotropy injection. Due to the inherent interaction of the system with its surrounding, the battery exhibits a self-discharge, which is shown to be described by a supercapacitor-like self-discharging mechanism. Our results paves the way for proposals of new superconducting circuits able to store extractable work for further usage.