A microwave-activated phase gate using a superconducting coupler for remote entanglement of two quantum dot qubits*

The extensibility of spin qubits in quantum dots is constrained by the dense connectivity required for multi-qubit gates. A modular architecture, enabled by an entangling gate between distant qubits, is a promising solution. Circuit QED techniques could facilitate such remote entanglement generation. Previous research has focused on transverse interactions between qubits and superconducting resonators [1] or transmons [2]. Approaches have also been suggested where longitudinal coupling is induced by drives applied to the dot qubits [3]. Alternatively, a coupler element can be driven instead of the qubit. Here, we propose a microwave-activated phase gate in which a superconducting coupler is driven to implement a CZ gate between two remote quantum dot qubits. The quantum dot qubits are longitudinally coupled to the coupler, allowing for gate speed that is not restricted by the dispersive limit. We present the appropriate pulse sequence, analytical expressions for gate fidelity, and estimated fidelity based on realistic parameters for various superconducting coupler elements.

[1] X. Mi. et al., Science 355, 2017.

[2] A. J. Landig et al., Nat. Commun. 10, 2019.

[3] C. G. L. Bøttcher, Nat. Commun. 13, 2022.