Quantum Cavity Optomechanics of Levitated Nanoparticles: from Foundations to Technologies

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Processes in the microscopic world are extremely well described by quantum theory, but yet little is known about the transition to the classical world at macroscopic scales. For example, can a macroscopic object such as a virus be put into a quantum superposition, and if not, what are the processes at these length and mass scales that prevent this? These types of questions are not only important for our fundamental understanding of the world but they will also impact on the development of future engineered macroscopic quantum systems. Until very recently these questions remained a primarily theoretical pursuit because the experimental methods required to prepare and maintain the delicate quantum states in the presence of environmental noise did not exist. This is because even weak interactions between a quantum system and its environment can rapidly destroy them. As such, these systems must be prepared in well controlled isolation, and typically, this often requires cooling to very low temperatures. New experimental techniques now offer the prospect for laboratory tests of macroscopic quantum mechanics. This field, collectively known as quantum cavity optomechanics, uses the controlled interaction of light with the mechanical motion of nanoscale and microscale oscillators, to coherently control their motion. To date quantum ground state cooling has been demonstrated in only a handful of these solid-state devices but a macroscopic superposition, and even non-classical motion, has yet to be observed. A new optomechanical oscillator system that is levitated in vacuum has recently been developed by the UCL group. It uses a novel configuration of electric and optical fields to achieve extremely good isolation from the environment. Cooling from room temperatures down to milliKelvin temperatures has been achieved for the first time, by employing a technique called cavity cooling, with quantum ground state cooling now within reach. Our aim in this research programme is to build on this initial success by using the hybrid technologies to create a well controlled, low dissipation macroscopic oscillator, that can be prepared in its absolute ground state. This system will allow us to explore macroscopic quantum mechanics by preparing and measuring its nonclassical motion. For the first time, we will undertake laboratory tests of theoretical models for macroscopic wavefunction collapse. This will be possible even when the system is not in the ground state. The very low noise and high mechanical Q of this oscillator system also offers significant promise for sensing applications. Therefore as part of this research programme we will begin to explore these more classical applications which includes the development of a new type of in-trap spectrometer capable of measuring mass, charge and shape of nanoparticles, while another strand will seek to use the tunable interactions between the levitated particle for controlling, switching and storing light fields.