Meissner-like Effect for a Synthetic Gauge Field in Multimode Cavity QED.

Previous realizations of synthetic gauge fields for ultracold atoms do not allow the spatial profile of the field to evolve freely. We propose a scheme which overcomes this restriction by using the light in a multimode cavity with many nearly degenerate transverse modes, in conjunction with Raman coupling, to realize an artificial magnetic field which acts on a Bose-Einstein condensate of neutral atoms. We describe the evolution of such a system and present the results of numerical simulations which show dynamical coupling between the effective field and the matter on which it acts. Crucially, the freedom of the spatial profile of the field is sufficient to realize a close analogue of the Meissner effect, where the magnetic field is expelled from the superfluid. This backaction of the atoms on the synthetic field distinguishes the Meissner-like effect described here from the Hess-Fairbank suppression of rotation in a neutral superfluid observed elsewhere.

There are many ways to spin a photon: Half-quantization of a total optical angular momentum.

The angular momentum of light plays an important role in many areas, from optical trapping to quantum information. In the usual three-dimensional setting, the angular momentum quantum numbers of the photon are integers, in units of the Planck constant h. We show that, in reduced dimensions, photons can have a half-integer total angular momentum. We identify a new form of total angular momentum, carried by beams of light, comprising an unequal mixture of spin and orbital contributions. We demonstrate the half-integer quantization of this total angular momentum using noise measurements. We conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization.

Photonic nanojets in Fresnel zone scattering from non-spherical dielectric particles.

We experimentally and numerically study near-field and far-field visible light scattering from lithographically defined micron scale dielectric particles. We demonstrate field confinement and elongated intensity features known as photonic nanojets in the Fresnel zone. An experimental setup is introduced which allows simultaneous mapping of the angular properties of the scattering in the Fresnel zone and far-field regions. Precise control over the shape, size and position of the scatterers, allows direction control of the near-field intensity distribution. Intensity features with 1/3 the divergence of free space Gaussian beams of similar waist are experimentally observed. Additionally the direction and polarization of the incident light can be used to switch on and off intensity hot spots in the near-field. Together these parameters allow a previously un-obtainable level of control over the intensity distribution in the near-field, compared to spherically and cylindrically symmetric scattering particles.