Decoding Polarization in a Single Achiral Gold Nanostructure from Emitted Far-Field Radiation.

The emergence of optical chirality in the light emitted from plasmonic nanostructures is commonly associated with their geometrical chirality. Although it has been demonstrated that even achiral structures can exhibit chiral near-fields, the existence of chiroptical far-field responses of such structures is widely neglected. In this paper, we present a detailed analysis of the polarization state in a single planar achiral plasmonic nanostructure that sustains more than one prominent plasmon mode. In consideration of the relative phase, the superposition of the fields associated with these modes determines the polarization state of the emitted light in the far-field. Supported by simulations of the surface charge distribution of the particle, we show that the polarization state of the emitted light is already determined in the near-field. The chiroptical far-field responses are analyzed by polarized single-particle dark-field scattering spectroscopy. We introduce an analytical model that enables us to obtain the polarization information from the spectra of structures with dipolar resonances taken under unpolarized illumination. The same principle is confirmed in polarimetric spectroscopy measurements on rhomboids with systematically varied angles, therefore, introducing increasing values of geometrical chirality to the structures. The agreement between the calculation and measurement demonstrates the general validity of our model for both chiral and achiral structures.

Manipulation and coherence of ultra-cold atoms on a superconducting atom chip.

The coherence of quantum systems is crucial to quantum information processing. Although superconducting qubits can process quantum information at microelectronics rates, it remains a challenge to preserve the coherence and therefore the quantum character of the information in these systems. An alternative is to share the tasks between different quantum platforms, for example, cold atoms storing the quantum information processed by superconducting circuits. Here we characterize the coherence of superposition states of (87)Rb atoms magnetically trapped on a superconducting atom chip. We load atoms into a persistent-current trap engineered next to a coplanar microwave resonator structure, and observe that the coherence of hyperfine ground states is preserved for several seconds. We show that large ensembles of a million of thermal atoms below 350 nK temperature and pure Bose-Einstein condensates with 3.5 × 10(5) atoms can be prepared and manipulated at the superconducting interface. This opens the path towards the rich dynamics of strong collective coupling regimes.