Enabling Modularity via Drive-Tunable Entanglement of Spin Qubits

Modularity [1] represents a promising path to scaling quantum processors but requires coherent qubit control and entanglement over a wide range of distances. Semiconductor quantum dots enable the realization of spin qubits in compact “artificial atom” systems with highly tailored features, such as large and tunable electric dipole moments that allow electric field control of spin qubits. While the exchange interaction between spins enables both rapid gates and coherence-protected qubit encodings with all-electrical control in this platform, the inherently short range of the interaction imposes constraints on the ultimate scalability of spin qubits. To address these challenges, we present an approach for entangling electrically controllable spin qubits within individual modules based on a longer-range Coulomb interaction mediated by an ac-driven multielectron mediator quantum dot that serves as a tunable semiconductor coupler. We show that rapid entangling gates between dressed qubits equivalent to the Mølmer-Sørensen gate for trapped ions [1] can be achieved for experimentally relevant parameters. We also describe how to integrate this intramodular coupling with a previously developed approach for intermodular coupling [2] via cavity photon-mediated entangling gates between parametrically driven spin qubits, in which the sidebands generated by the driving fields enable tunability and spectral flexibility. Our work suggests a promising route to scalability for spin-based quantum processors via modularity. 

[1] C. Monroe, R. Raussendorf, A. Ruthven, K. R. Brown, P. Maunz, L.-M. Duan, and J. Kim, Phys. Rev. A 89, 022317 (2014).

[2] V. Srinivasa, J. M. Taylor, and J. R. Petta, PRX Quantum 5, 020339 (2024).