Fundamental constraints on particle tracking with optical tweezers

TL;DR

This paper derives a quantum limit for particle position measurement sensitivity in optical tweezers, showing current experiments are close to this fundamental boundary and highlighting potential for quantum-enhanced tracking.

Contribution

It establishes a quantum sensitivity limit for optical tweezers and evaluates experimental proximity to this limit, considering particle size and power requirements.

Findings

Quantum limit derived using Heisenberg microscope principle

Current experiments are within two orders of magnitude of the quantum limit

Optimal particle diameter for zero-point motion observation is smaller than wavelength

Abstract

A general quantum limit to the sensitivity of particle position measurements is derived following the simple principle of the Heisenberg microscope. The value of this limit is calculated for particles in the Rayleigh and Mie scattering regimes, and with parameters which are relevant to optical tweezers experiments. The minimum power required to observe the zero-point motion of a levitating bead is also calculated, with the optimal particle diameter always smaller than the wavelength. We show that recent optical tweezers experiments are within two orders of magnitude of quantum limited sensitivity, suggesting that quantum optical resources may soon play an important role in high sensitivity tracking applications.