On the classical resolution limit of particle position measurement with optical tweezers

Optical tweezers have many fundamental and commercial applications (Grier, 2003) ranging from trapping and transportation of cold atoms, to investigations of cellular structure and the properties of DNA. Many of these applications are enabled by the ability of optical tweezers to monitor the position of particles with sub-nanometre resolution. In applications such as nano-engineering and single particle diffusion studies, the particle position itself is the parameter of interest; whilst in other applications such as research into protein interactions, it is used to infer other parameters such as elasticity, or an applied force. The resolution of position measurement with classical optical fields is fundamentally limited by shotnoise due to quantization of the field, and by the specific design of the detection device while the inference of other parameters typically suffers a further limitation due to particle diffusion. Here we report on investigations of the combined classical resolution limit to particle position measurement imposed by the first two limitations.