Konstantin Kalashnikov

Flip-Chip Packaging of Fluxonium Qubits

  1. Aaron Somoroff,
  2. Patrick Truitt,
  3. Adam Weis,
  4. Jacob Bernhardt,
  5. Daniel Yohannes,
  6. Jason Walter,
  7. Konstantin Kalashnikov,
  8. Raymond A. Mencia,
  9. Igor V. Vernik,
  10. Oleg Mukhanov,
  11. Maxim G. Vavilov,
  12. and Vladimir E. Manucharyan
The strong anharmonicity and high coherence times inherent to fluxonium superconducting circuits are beneficial for implementing quantum information processors. In addition to requiring
high-quality physical qubits, a quantum processor needs to be assembled in a manner that reduces crosstalk and decoherence. In this letter, we report work on fluxonium qubits packaged in a flip-chip architecture. Here, the fluxonium qubits are embedded in a multi-chip module (MCM), where a classical control and readout chip is bump-bonded to the quantum chip. The modular approach allows for improved connectivity between qubits and control/readout elements, and separate fabrication processes. We demonstrate that this configuration does not degrade the fluxonium qubit performance, and identify the main decoherence mechanisms to improve on the reported results.
arxiv pdf

Bifluxon: Fluxon-Parity-Protected Superconducting Qubit

  1. Konstantin Kalashnikov,
  2. Wen Ting Hsieh,
  3. Wenyuan Zhang,
  4. Wen-Sen Lu,
  5. Plamen Kamenov,
  6. Agustin Di Paolo,
  7. Alexandre Blais,
  8. Michael E. Gershenson,
  9. and Matthew Bell
We have developed and characterized a symmetry-protected superconducting qubit that offers simultaneous exponential suppression of energy decay from charge and flux noise, and dephasing
from flux noise. The qubit consists of a Cooper-pair box (CPB) shunted by a superinductor, thus forming a superconducting loop. Provided the offset charge on the CPB island is an odd number of electrons, the qubit potential corresponds to that of a cosϕ/2 Josephson element, preserving the parity of fluxons in the loop via Aharonov-Casher interference. In this regime, the logical-state wavefunctions reside in disjoint regions of phase space, thereby ensuring the protection against energy decay. By switching the protection on, we observed a ten-fold increase of the decay time, reaching up to 100μs. Though the qubit is sensitive to charge noise, the sensitivity is much reduced in comparison with the charge qubit, and the charge-noise-induced dephasing time of the current device exceeds 1μs. Implementation of the full dephasing protection can be achieved in the next-generation devices by combining several cosϕ/2 Josephson elements in a small array.
arxiv pdf