Optically Driven Rotation of Exciton-Polariton Condensates.

The rotational response of quantum condensed fluids is strikingly distinct from rotating classical fluids, especially notable for the excitation and ordering of quantized vortex ensembles. Although widely studied in conservative systems, the dynamics of rotating open-dissipative superfluids such as exciton-polariton condensates remains largely unexplored, as it requires high-frequency rotation while avoiding resonantly driving the condensate. We create a rotating polariton condensate at gigahertz frequencies by off-resonantly pumping with a rotating optical stirrer composed of the time-dependent interference of two frequency-offset, structured laser modes. Acquisition of angular momentum exceeding the critical 1ℏ/particle is directly measured, accompanied by the deterministic nucleation and capture of quantized vortices with a handedness controlled by the pump rotation direction. The demonstration of controlled optical rotation of a spontaneously formed polariton condensate enables new opportunities for the study of open dissipative superfluidity, ordering of non-Hermitian quantized vortex matter, and topological states in a highly nonlinear, photonic platform.

Interrogating Nanojunctions Using Ultraconfined Acoustoplasmonic Coupling.

Single nanoparticles are shown to develop a localized acoustic resonance, the bouncing mode, when placed on a substrate. If both substrate and nanoparticle are noble metals, plasmonic coupling of the nanoparticle to its image charges in the film induces tight light confinement in the nanogap. This yields ultrastrong "acoustoplasmonic" coupling with a figure of merit 7 orders of magnitude higher than conventional acousto-optic modulators. The plasmons thus act as a local vibrational probe of the contact geometry. A simple analytical mechanical model is found to describe the bouncing mode in terms of the nanoscale structure, allowing transient pump-probe spectroscopy to directly measure the contact area for individual nanoparticles.

A sub-femtojoule electrical spin-switch based on optically trapped polariton condensates.

Practical challenges to extrapolating Moore's law favour alternatives to electrons as information carriers. Two promising candidates are spin-based and all-optical architectures, the former offering lower energy consumption, the latter superior signal transfer down to the level of chip-interconnects. Polaritons-spinor quasi-particles composed of semiconductor excitons and microcavity photons-directly couple exciton spins and photon polarizations, combining the advantages of both approaches. However, their implementation for spintronics has been hindered because polariton spins can be manipulated only optically or by strong magnetic fields. Here we use an external electric field to directly control the spin of a polariton condensate, bias-tuning the emission polarization. The nonlinear spin dynamics offers an alternative route to switching, allowing us to realize an electrical spin-switch exhibiting ultralow switching energies below 0.5 fJ. Our results lay the foundation for development of devices based on the electro-optical control of coherent spin ensembles on a chip.