A Compact Planar Multi-Modal Device for Efficient Error-Suppression Encoding

One of the major challenges in achieving fault-tolerant quantum computing has been the fidelity of two-qubit entangling gates. Traditional 2-qubit gates typically rely on transverse coupling, which introduces an additional ZZ interaction term. This term often leads to spectator errors and contributes to qubit dephasing. Although weak ZZ coupling can introduce errors that require external drives to correct, strong ZZ coupling can be advantageous. In this talk, we present a planar version of a multimodal device, commonly called a Trimon, which features three qubit-like modes A, B and C, with strong, all-to-all longitudinal coupling. Our 2D implementation uses two CPW readout resonators to couple modes A and C, and B and C, respectively enabling faster readout and control compared to its 3D counterpart. We also discuss how this compact design of longitudinally coupled three-qubit modes can enable fast multi-qubit gates allowing us to construct decoherence-free subspaces, and thus improving the system's robustness against offset-charge errors.