Engineering conditional displacement gates in superconducting circuits via direct drive on a nonlinear auxiliary

Conditional displacement gates, together with arbitrary auxiliary rotations, enable universal control of the state of an oscillator and serve as a natural entangling gate for bosonic codes based on grid codes [1,2]. The most common implementation in superconducting circuits is the so-called echoed conditional displacement (ECD) [1,2]. This oscillator-driven ECD consists of displacing the oscillator state to amplify the conditional rotation with a nonlinear auxiliary that originates from a weak dispersive interaction.

While ECDs have enabled the experimental demonstration of state preparation and quantum error correction of single-mode grid states [1-4], further improvements in gate fidelity are required. Inspired by the work of Touzard et al. [5], we experimentally demonstrate an ECD gate implemented by directly driving the auxiliary at the oscillator frequency. This implementation may reduce susceptibility to intrinsic cavity dephasing and mitigate crosstalk in a scaled processor. We will present preliminary experimental results regarding the calibration of the auxiliary-driven ECDs and comparison with their oscillator-driven counterpart.



[1] A. Eickbusch et al., Nature Physics 18, 1464 (2022)

[2] P. Campagne-Ibarcq et al., Nature 584, 368 (2020)

[3] V. V. Sivak et al., Nature 616, 55 (2023)

[4] D. Lachance-Quirion et al., Phys. Rev. Lett. 132, 150607 (2024)

[5] S. Touzard et al., Phys. Rev. Lett. 122, 080502 (2019)