Research Highlights

Self-organization of ultracold atoms in optical resonators is often used for analog simulation of models relevant to quantum optics and many-body physics, such as the Dicke model or models with U(1) symmetry. Steady state experimental results in this domain can usually be explained in the semiclassical approximation, where quantum correlations between atomic degrees of freedom are negligible. 

In this work, using a fully quantum description, we theoretically and numerically demonstrate that spontaneous generation of significant multiparticle entanglement in atomic momentum can occur in the transient. The high efficiency of entanglement generation is here caused by the runaway dynamics at the onset of atomic self-organization. Two theoretical models were studied, one based on light-mediated interaction of ultracold atoms placed in a laser driven ring resonator, and the other based on direct collisions between ultracold atoms in an oscillating magnetic field. Numerical calculations show that this method could potentially be highly efficient in generating quantum entangled atoms even in so-called “bad resonators”. The discovery opens the door to new opportunities for studying quantum correlations, not only using ultracold atoms, but other types of nonlinear media as well.

Propagation through an inhomogeneous medium, such as fog, can severely degrade the shape of a beam of light due to complex scattering processes. In this Article, we have extended the framework of constant-intensity waves to a novel system – a synthetic photonic lattice built by interfering pulses of light propagating through a fiber, in order to remove the beam degradation caused by the scattering. The mechanism preserves the intensity distribution of the incoming beam, by mitigating destructive interference via gain and constructive interference via loss, with a tailored non-Hermitian lattice. This experiment marks a first demonstration of shape-preserved propagation and induced transparency for electromagnetic waves on a discrete non-Hermitian lattice, and is a step towards potential real-world realizations of transparent media based on gain and loss.

Transformation optics is a fascinating framework connecting the geometry of space with propagation of light through a medium. It is commonly known that materials with isotropic optical response can be generated by conformal transformations of free space, which locally preserve the angles between lines. In our recent article, we have demonstrated that, with certain caveats, also non-conformal transformations can be used to mould light propagation in isotropic materials. The condition is that now, in contrast to the previous case, the medium generated by the transformation is tied to the electric field solution in free space. Also, in contrast to the previous case, the non-conformality leads now to a modulation in the imaginary part of the refractive index distribution, i.e. gain and loss. We have used these insights to design a two-dimensional unidirectional cloak with an isotropic non-Hermitian dielectric material, which now works also for light pulses, in contrast to similar cloaks generated with conformal transformations.

The engineering of light confinement in disordered materials is made difficult by the presence of multiple scattering, which causes the inhomogeneous electric field distribution to be highly dependent on local changes of the refractive index. Here, we present a theoretical methodology for modifying disordered 1D Hermitian dielectric index distributions in order to increase or reduce the electric field at a given location, by using a transformation of the electric field distribution of the initial system. Intriguingly, the electric fields related by such field transformations are indistinguishable to the outside observer in both amplitude and phase, at frequencies near the design frequency. We apply our methodology to both continuous and discrete refractive index distributions, considering also the potential experimental implementations.