A compact 3-qubit multimodal circuit with universal control

Achieving fault-tolerant quantum computing requires high fidelity multi-qubit entangling gates. Conventional gate schemes often rely on additional circuit elements such as tunable couplers, which often implement only a very small subset of two qubit gates. These coupler induced interactions can also generate parasitic ZZ terms, leading to spectator errors and qubit dephasing that degrade overall gate performance. Although weak ZZ coupling can introduce errors that require external drives to correct, strong ZZ coupling can be advantageous. In this work, 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 planar implementation uses two quarter-wave readout resonators to dispersively couple to modes A and C, and B and C, respectively, enabling more efficient readout, along with a charge line that improves control speeds compared to its 3D counterpart. We show that this compact, dispersively coupled multimodal architecture supports various multi-qubit gates including iSWAP, cSWAP and B Gates. We also demonstrate the versatility of this platform for qudit operations and the implementation of error suppression mechanisms such as erasure qubits, providing a way to bring down logical error rates of the system.