Double-quantum dot spin qubits in coupled microwave cavities

Scaling spin-qubits in Si while maintaining precise control over their interactions is a crucial challenge in developing quantum computing hardware. Petta et al. [1] realized a promising setup by placing double-quantum dots (DQD) in a microwave cavity, enhancing the dipole interaction with micromagnets to induce an effective spin-orbit coupling. While typical cavities can accommodate hundreds or thousands of DQDs, our studies demonstrate that increasing the number of qubits significantly diminishes the transmission amplitude and reduces individual qubit control.

As an alternative, we explored models of two and three-coupled cavities, each containing one qubit. Using a tight-binding formulation in the single photon exchange regime and applying input-output theory [2], we derived the Langevin equations for photon and qubit operators for linear and triangular cavity arrays. We analyzed two configurations: 1) input and output signals connected to the same cavity and 2) signals connected to different cavities to investigate how varying coupling intensities and frequencies affect the transmission signal. Our results show that these setups offer greater tunability with additional resonant frequencies and allow individual qubits to be addressed more flexibly, yielding robust transmission signals across a broad range of coupling intensities and frequency mismatches.

[1] X. Mi, J. V. Cady, D. M. Zajac, P. W. Deelman and J.R. Petta, Science 335, 156 (2017)

[2] M. Benito, X. Mi, J. M. Taylor, J. R. Petta, and G. Burkard, Phys. Rev. B 96, 235434 (2017).