Non-Hermitian dynamics and nonreciprocity of two optically coupled nanoparticles

Optical levitation of dielectric objects in vacuum provides a unique optomechanical platform due to versatile optical control of potentials and good isolation from the environment. Recently, tunable and nonreciprocal optical interactions have been measured between two nanoparticles, levitated in two distinct optical tweezers, with single-site readout of particle motion. I will present our experimental platform for tweezer arrays of nanoparticles, and show our recent results on non-Hermitian collective dynamics of two nonreciprocally interacting nanoparticles. We also observe a mechanical lasing transition once a threshold coupling rate is achieved, supported by our nonlinear theory model. Nonreciprocal interactions are expected to result in an even richer phase diagram of nonequilibrium dynamics for larger arrays of nanoparticles. This work paves the way towards upscaling this platform to such multiparticle arrays, in view of studying their nonequilibrium and collective mechanical behaviour in the quantum regime.