High-fidelity regimes of resonator-mediated controlled-Z gates between quantum-dot qubits

TL;DR

This paper investigates high-fidelity controlled-Z gates between quantum-dot qubits mediated by resonators, emphasizing the importance of going beyond the rotating-wave approximation to optimize gate fidelity, especially for charge qubits.

Contribution

It introduces a novel parametric drive for charge qubits that reduces errors and demonstrates superior fidelity and robustness over spin qubits by going beyond RWA.

Findings

Charge qubits achieve a fidelity loss of only 0.05%

Charge qubits are more robust against drive amplitude variations

Going beyond RWA is essential for high-fidelity long-range gates

Abstract

Semiconductor double quantum dot (DQD) qubits coupled via superconducting microwave resonators provide a powerful means of long-range manipulation of the qubits' spin and charge degrees of freedom. Quantum gates can be implemented by parametrically driving the qubits while their transition frequencies are detuned from the resonator frequency. Long-range two-qubit controlled-Z (CZ) gates have been proposed for the DQD spin qubit within the rotating-wave approximation (RWA). Rapid gates demand strong coupling, but RWA breaks down when coupling strengths become significant relative to system frequencies. Therefore, understanding the errors arising from approximations used is critical for high-fidelity operation. Here, we go beyond RWA to study CZ gate fidelity for both DQD spin and charge qubits. We propose a novel parametric drive on the charge qubit that produces smaller errors and show that the fidelity of the CZ gate outperforms its spin counterpart, resulting in a much smaller fidelity loss of $0.05\%$ compared to $0.80\%$ for the spin qubit, and greater robustness against qubit dephasing and photon loss. We find that drive amplitude -- a parameter dropped in RWA -- is critical for optimizing fidelity, with the charge qubit exhibiting better tolerance to drive amplitude variations. Our results demonstrate the necessity of going beyond RWA in understanding how long-range gates can be realized in DQD qubits, with charge qubits offering considerable advantages in high-fidelity operation.