Spin qubits in photon-coupled microwave cavites

Electron spin qubits in microwave cavities represent a promising foundation for developing quantum computing hardware. Electron spin states have high coherence times compared to gate interaction time scales, and photon coupling allows for long-distance interaction between qubits. The strong spin-photon coupling regime can be realized via the dipole interaction, as Petta et al. [1] demonstrated by placing an electron in a double quantum dot (DQD) with a magnetic field gradient inside a microwave cavity. These studies later included two DQDs inside the cavity to demonstrate long-range spin-spin interactions [2]. Input/output theory describes the system's behavior when driven by an external field and determine the internal qubits states from the transmission amplitude of the output field [3]. Our studies showed that additional qubits inside the cavity render lower transmission amplitudes. As an alternative setup, we analyze results from a model of a double DQD qubit system consisting of two cavities, each containing one qubit, coupled via a photonic waveguide that allows for single photon exchange. In analogy with previous works, we utilize input/output theory to obtain transmission amplitudes and discuss the various regimes determined by tuning different parameters.