Scalable 3D quantum memory

  1. Edwar Xie,
  2. Frank Deppe,
  3. Daniel Repp,
  4. Peter Eder,
  5. Michael Fischer,
  6. Jan Goetz,
  7. Stefan Pogorzalek,
  8. Kirill G. Fedorov,
  9. Achim Marx,
  10. and Rudolf Gross
Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit both to a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. The external coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of 6 with a Z-fidelity of 82%. We also find that this enhancement is not limited by fundamental constraints.

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