Microwave-optics quantum frequency conversion and optically heralded microwave photons

The internet has greatly changed the way we live our daily lives. One of the enabling components of the internet is the telecom transceiver. It converts information in the electrical signals from our phones and laptops, to variations of light in an optical fiber, where the light propagates kilometers without significant loss. Similar to how the internet revolutionized processing of classical information, a quantum internet that connects different quantum systems could enable secure communication, powerful new computers and sensors. Superconducting circuits form one of the leading platforms for manipulating quantum information, offering great nonlinearity, decent coherence, and accessible control and readout. However, they operate at millikelvin temperatures with microwave photons, which are easily overwhelmed by loss and thermal noise at room temperature. As a result, quantum frequency converters between microwave and telecom photons that resemble the classical transceivers are desired. In this dissertation, I will describe our efforts towards realizing such a converter. Our approach utilizes a gigahertz mechanical resonance as an intermediary between microwave and optics. I will first discuss how we strongly couple telecom frequency photons and gigahertz mechanical vibrations with cavity-optomechanics. Such coupling offers the nonlinearity required for the frequency conversion. Meanwhile, the mechanical vibrations can be driven and readout with microwave circuits using piezoelectric effect. To realize this two-step conversion process, we began with design and fabrication of optomechanical crystals using an emerging photonic circuit material platform, thin-film lithium niobate, which also possess great piezoelectric properties. I will uncover the challenges and solutions of using piezoelectric effect to drive and readout the mechanical resonance with interdigital transducers and microwave circuits. Improving the optomechanical interaction eventually led us to a hybridized material platform of lithium niobate on silicon on insulator. Combining efficient optomechanical and piezoelectric coupling resulted in a fully integrated converter with unprecedented efficiency to let us observe a microwave photon from the device heralded by optical single photon detection. The potential improvements and applications of our converter are discussed