ZZ-Free bSWAP Gates under Strong Driving in Far-Detuned Fixed-Frequency Transmons

  1. Akinori Machino,
  2. Kazuhisa Ogawa,
  3. Yuto Ikegai,
  4. Takafumi Miyanaga,
  5. Koichiro Ban,
  6. Nilton F. G. Filho,
  7. Hidehisa Shiomi,
  8. Toshi Sumida,
  9. Shuhei Tamate,
  10. Yutaka Tabuchi,
  11. Yasunobu Nakamura,
  12. and Makoto Negoro
Far-detuned frequency allocations in fixed-frequency superconducting processors mitigate spectral crowding but constrain cross-resonance interactions at practical drive amplitudes. Here, we demonstrate that a single strong drive induces a large XX−YY interaction in the far-detuned regime, while a weak second tone tunes the accompanying ZZ phase. The interaction realizes a 150-ns bSWAP‾‾‾‾‾‾‾‾√ gate, which can directly prepare a maximally entangled state from the ground state. For the implementations on the same qubit pair at matched drive strengths, cross resonance gives a shorter CNOT operation, while bSWAP‾‾‾‾‾‾‾‾√ gives a 33% shorter SWAP operation with a higher IRB fidelity. The multilevel theory further predicts a regime where stronger driving can yield a speed advantage for CNOT as well, a possibility absent in the two-level model. As an application of the XX−YY interaction, we also demonstrate two-spin squeezing beyond the standard quantum limit through two-axis countertwisting. The interaction realized here complements cross resonance and offers a route to efficient gate synthesis and quantum simulation of interacting spin systems.
arxiv pdf

leave comment