A. Petrescu

Dynamically enhancing qubit-oscillator interactions with anti-squeezing

  1. M. Villiers,
  2. W. C. Smith,
  3. A. Petrescu,
  4. A. Borgognoni,
  5. M. Delbecq,
  6. A. Sarlette,
  7. M. Mirrahimi,
  8. P. Campagne-Ibarcq,
  9. T. Kontos,
  10. and Z. Leghtas
The interaction strength of an oscillator to a qubit grows with the oscillator’s vacuum field fluctuations. The well known degenerate parametric oscillator has revived interest
in the regime of strongly detuned squeezing, where its eigenstates are squeezed Fock states. Owing to these amplified field fluctuations, it was recently proposed that squeezing this oscillator would dynamically boost its coupling to a qubit. In a superconducting circuit experiment, we observe a two-fold increase in the dispersive interaction between a qubit and an oscillator at 5.5 dB of squeezing, demonstrating in-situ dynamical control of qubit-oscillator interactions. This work initiates the experimental coupling of oscillators of squeezed photons to qubits, and cautiously motivates their dissemination in experimental platforms seeking enhanced interactions.
arxiv pdf

Multipartite Entanglement in Rabi Driven Superconducting Qubits

  1. M. Lu,
  2. J. L. Ville,
  3. J. Cohen,
  4. A. Petrescu,
  5. S. Schreppler,
  6. L. Chen,
  7. C. Jüenger,
  8. C. Pelletti,
  9. A. Marchenkov,
  10. A. Banerjee,
  11. W. Livingston,
  12. J.M. Kreikebaum,
  13. D. Santiago,
  14. A. Blais,
  15. and I. Siddiqi
Exploring highly connected networks of qubits is invaluable for implementing various quantum algorithms and simulations as it allows for entangling qubits with reduced circuit depth.
Here, we demonstrate a multi-qubit STAR (Sideband Tone Assisted Rabi driven) gate. Our scheme is inspired by the ion qubit Mølmer-Sørensen gate and is mediated by a shared photonic mode and Rabi-driven superconducting qubits, which relaxes restrictions on qubit frequencies during fabrication and supports scalability. We achieve a two-qubit gate with maximum state fidelity of 0.95 in 310 ns, a three-qubit gate with state fidelity 0.905\% in 217 ns, and a four-qubit gate with state fidelity 0.66 in 200 ns. Furthermore, we develop a model of the gate that show the four-qubit gate is limited by shared resonator losses and the spread of qubit-resonator couplings, which must be addressed to reach high-fidelity operations.
arxiv pdf