Reducing Added Noise in a Microwave-Mechanical-Optical Converter

Viewed as resources for quantum information processing, microwave and optical fields offer complementary strengths. Quantum technologies operating at microwave frequencies have shown the ability to create and manipulate quantum information, making them leading candidates for building a quantum computer. Optical fields can transmit quantum information over long distances with low loss making them ideal for use as links between quantum nodes. Therefore the ability to transduce quantum information between microwave and optical frequencies is an essential technology in realizing an extended quantum network. To date there has been no demonstration of a microwave to optical link that is capable of quantum transduction.

This thesis describes the design and characterization of a device that couples one mode of a micromechanical oscillator to a resonant microwave circuit and a high-finesse optical cavity, thereby realizing a mechanically mediated electro-optic converter. We have operated this converter at T < 100 mK, and demonstrated unprecedented conversion efficiency of 47% and added noise of 38 photons. I discuss how noise correlations can be exploited to develop a feedforward protocol. I also discuss the limitations on the noise performance of the device used to achieve these results, and describe recent improvements in the fabrication process and optical and microwave resonator designs aimed at reducing added noise. These improvements should produce a device that is near the threshold for quantum conversion.