Publication
In the same year as Einstein's annus mirabilis, English engineer and physicist John Flemming patented the first rectifying diode, which he called the "Flemming valve". Einstein's work on the photoelectric effect would change our understanding of the nature of light - a pivotal moment in the development of quantum theory. Flemming's diode would transform our world as well, often pointed to as the beginning of modern electronics. These ideas, born in the same moment, have remained entwined. Quantum theory has been fundamental to transistor development, and that, in turn, led to the computer revolution and accompanying development of silicon manufacturing. The theoretical and technological gifts these ideas have accumulated over the past hundred years are now laid to bare in the field of cavity optomechanics. The silicon technology that owes its very existence to quantum theory is now leveraged to test the limitations of theory and perhaps to exploit quantum resources for a new class of sensors. Micro-, and even nano-scale, optical cavities are coupled to commensurately miniaturized mechanical oscillators, where strong radiation pressure mediated interactions between their corresponding modes can be realized. The fluctuating position of a mechanical element is imprinted on the phase of light circulating within the cavity, while the varying amplitude of the light alters its momentum. Quantum fluctuations are imprinted on the mechanical element by light within the cavity, establishing correlations between its phase and amplitude. Utilizing the optomechanical system developed in this thesis work we are able to observe the signature of these induced correlations, even in the presence of thermal noise at room-temperature. Moreover, we demonstrate the principle by which correlations can be used to cancel measurement back-action, producing a quantum-enhanced sensitivity to external forces. The system in question is also demonstrated to achieve an imprecision more than three orders of magnitude below that at the standard quantum, at room-temperature, which is unprecedented. A strong radiation pressure interaction between a micron-scale mechanical element and an optical cavity has been achieved by taking advantage of many of the powerful tools developed in the context of building modern computers. Using transistor technology in this new context we engineer an optomechanical system that exhibits an exceptionally large contribution of back-action relative to thermal noise. In addition to observing this back-action signature at ambient temperatures, the large interaction strength is applied to the task of laser cooling with a measurement-based feedback scheme. In this framework, we demonstrate the ability to reduce the thermal occupation of a cryogenically cooled mechanical mode by an additional three orders of magnitude, to a mean occupancy of just 5.3 phonons.