High-impedance circuit quantum electrodynamics with semiconductor quantum dots

Spin qubits are a promising contender for quantum information technology. However, spin-entangling gates are short range and a long-range coupler is required for achieving scalability. To this aim, strong coupling between a spin qubit and a photon is highly desirable.

In this thesis, we realize several architectures based on high-impedance resonators which enhance the coupling strength between semiconducting qubits and a single resonator photon.

Using a double dot in GaAs and a flux-tunable SQUID-array resonator, we demonstrate a systematic tuning strategy which allows engineering of the dipolar interaction strength between the resonator and a charge qubit as well as of the charge qubit coherence. Utilizing a junction-array resonator with even larger impedance, ultrastrong charge-qubit photon coupling is demonstrated in the resonant regime.

We then turn towards spin qubits by integrating semiconducting nanowires with magnetic-field resilient resonators based on NbTiN and demonstrate gate-dispersive charge sensing of a double dot defined in a Ge/Si core/shell nanowire.

Finally, we exploit the intrinsic spin-orbit interaction, present in crystal-phase defined double dots in InAs nanowires, for defining a singlet-triplet qubit and reach strong spin-photon coupling.