PhD Thesis Defense
Superconducting qubits that operate at microwave frequencies are one of the most promising platforms for quantum information processing. However, connecting distant processors with microwave photons is challenging since microwave photons suffer from thermal noise and large propagation losses in room temperature components. Conversely, optical photons within the telecommunications band are known to have extremely low loss in optical fiber and the thermal noise is minuscule at room temperature. In order to interface superconducting qubits with room temperature optical photons, a quantum transducer is required that can convert photons between microwave and optical frequencies.
Here, we developed a microwave-to-optical transducer using an ensemble of erbium ions, doped within a yttrium orthovanadate (YVO) crystal, that are simultaneously coupled to a superconducting microwave resonator and a photonic crystal optical resonator. The erbium ions have spin transitions that couple to the microwave resonator and optical transitions at telecom wavelengths that couple to the optical resonator. The transducer was characterized within a dilution refrigerator. We measured the coupling of the ions to the cavities and determine the influence of optical light on the microwave resonator and ions. The transducer efficiency is characterized in several different modes of operation including continuous-wave operation and pulsed operation with single photon detection. Lastly, the temperature of components within the transducer including the erbium ions and the microwave resonator are characterized during operation of the transducer. These results represent the first demonstration of a rare-earth ion transducer with integrated microwave and optical resonators.