The QUantum Control of Levitated Nanoparticle (QUCLN) project set out to explore quantum mechanics on an unprecedented mass scale. Exploiting the tools developed during the past decade in the field of optomechanics, while also developing new methods, we studied the interaction between optical fields and a dielectric nanoparticle trapped in an electrodynamic trap (i.e. a Paul trap). The main objectives of this study were to bring the levitated nanoparticle platform into the quantum regime by generating and observing quantum states of motion of the particle’s centre-of-mass motion, and to use non-interferometric techniques in these isolated systems to test conjectured models for the collapse of the quantum mechanical wavefunction.
There is an underling common motivation between these two lines of research. That is, we wanted to start to answer a seemingly simple question: does quantum mechanics provide a good description of the behaviour of systems on any mass scale by using levitated masses far larger than the typical atomic systems that we know are described by quantum mechanics?
Quantum mechanics has been placed under increasingly higher scrutiny but has always proven to provide a very accurate description of the microscopic world. Yet the question still remains, can the superposition of a system, where a particle is simultaneously in two different locations, be created at any scale and for any separation? Is there an intrinsic, yet unknown, limit to this fundamental principle of quantum mechanics?
Bringing a levitated oscillator into the quantum regime is the first necessary step toward the creation of these quantum superposition states. However, even without entering the quantum regime, there can be clues as to whether such a superposition can be realized. Indeed, a range of collapse models predict measurable effects even for classical systems.
Throughout the duration of the project we have made significant progress towards the observation of the motional ground state of a levitated nanoparticle and have made tests of collapse models. We have understood the noise and decoherence processes that prevent the creation of delicate quantum states and have developed our understanding and the tools required to mitigate them. We are now on the verge of using these methods to reach this demanding experimental regime. Even now, the technological advancements which have been made during this project have allowed us to create a charge particle nanoscale oscillator which has only very recently been used to place important new constraints on two collapse models.
