The discovery of artificial gauge fields controlling the dynamics of uncharged particles that otherwise elude the influence of standard electromagnetic fields has revolutionised the field of quantum simulation. Hence, developing new techniques to induce these fields is essential to boost quantum simulation of photonic structures. Here, we experimentally demonstrate the generation of an artificial gauge field in a photonic lattice by modifying the topological charge of a light beam, overcoming the need to modify the geometry along the evolution or impose external fields. In particular, we show that an effective magnetic flux naturally appears when a light beam carrying orbital angular momentum is injected into a waveguide lattice with a diamond chain configuration. To demonstrate the existence of this flux, we measure an effect that derives solely from the presence of a magnetic flux, the Aharonov-Bohm caging effect, which is a localisation phenomenon of wavepackets due to destructive interference. Therefore, we prove the possibility of switching on and off artificial gauge fields just by changing the topological charge of the input state, paving the way to accessing different topological regimes in a single structure, which represents an important step forward for optical quantum simulation.

Artificial gauge fields the control over the dynamics of uncharged particles by engineering the potential landscape such that the particles behave as if effective external fields are acting on them. Recent years have witnessed a growing interest in artificial gauge fields generated either by the geometry or by time-dependent modulation, as they have been enablers of topological phenomena and synthetic dimensions in many physical settings, e.g., photonics, cold atoms, and acoustic waves. Here, we formulate and experimentally demonstrate the generalized laws of refraction and reflection at an interface between two regions with different artificial gauge fields. We use the symmetries in the system to obtain the generalized Snell law for such a gauge interface and solve for reflection and transmission. We identify total internal reflection (TIR) and complete transmission and demonstrate the concept in experiments. In addition, we calculate the artificial magnetic flux at the interface of two regions with different artificial gauge fields and present a method to concatenate several gauge interfaces. As an example, we propose a scheme to make a gauge imaging system—a device that can reconstruct (image) the shape of an arbitrary wavepacket launched from a certain position to a predesigned location.

Topological materials have been at the forefront of research across various fields of physics in hopes of harnessing properties such as scatter-free transport due to protection from defects and disorder. Photonic systems are ideal test beds for topological models and seek to profit from the idea of topological robustness for applications. Recent progress in 3D-printing of microscopic structures has allowed for a range of implementations of topological systems. We review recent work on topological models realized particularly in photonic crystals and waveguide arrays fabricated by 3D micro-printing. The opportunities that this technique provides are a result of its facility to tune the refractive index, compatibility with infiltration methods, and its ability to fabricate a wide range of flexible geometries.

The rich physical properties of multiatomic crystals are determined, to a significant extent, by the underlying geometry and connectivity of atomic orbitals. The mixing of orbitals with distinct parity representations, such as s and p orbitals, has been shown to be useful for generating systems that require alternating phase patterns, as with the sign of couplings within a lattice. Here we show that by breaking the symmetries of such mixed-orbital lattices, it is possible to generate synthetic magnetic flux threading the lattice. We use this insight to experimentally demonstrate quadrupole topological insulators in two-dimensional photonic lattices, leveraging both s and p orbital-type modes. We confirm the nontrivial quadrupole topology by observing the presence of protected zero-dimensional states, which are spatially confined to the corners, and by confirming that these states sit at mid-gap. Our approach is also applicable to a broader range of time-reversal-invariant synthetic materials that do not allow for tailored connectivity, and in which synthetic fluxes are essential.

The surface photovoltage caused by band-to-band generation within the semiconductor depends on light intensity. This dependence differs significantly in two limiting cases. When recombination via fast surface states is negligible, the slope of the photovoltage versus the logarithm of intensity is always less than k T / e and depends on the amount of semiconductor band bending in the dark. When recombination via fast surface states becomes strong, this slope is k T / e , independent of the band bending. These differences are experimentally observed using a structure with ferroelectric NaNO, deposited on a real silicon surface. The switching of the direction of the spontaneous polarization of the ferroelectric results in significant changes of the semiconductor band bending in the dark. The charge exchange with slow surface states results in a continuous change of the band bending in the dark. The measurements reveal a pronounced minimum of the density of fast surface states near mid-gap. The results compare well to those from measurements on a field effect transistor structure with NaNO, as gate insulator.Die Photospannung einer Halbleiterrandschicht bei Anregung aus dem Valenz-ins Leitungsband hangt von der Lichtintensitat ab. Diese Abhangigkeit ist in zwei Grenzfallen deutlich verschieden. Tragt man die Photospannung uber dem Logarithmus der Intensitat auf, so findet man in beiden Fallen einen Bereich hearer Abhangigkeit. 1st die Rekombination iiber schnelle Grenzflachenzustande vernachIassigbar, so ist die Steigung immer kleiner als k T / e . Sie hangt dariiber hinaus noch von der Bandverbiegung im Dunkeln ab. Wird die Rekombination stark, so betragt die Steigung k T / e , unabhangig von der Bandverbiegung im Dunkeln. Diese Unterschiede werden an einer Struktur aus ferroelektrischem NaN0, auf der mit naturlichem Oxid bedeckten Siliziumoberflache experimentell beobachtet. Durch Umkehr der spontanen Polarisation des Ferroelektrikums laDt sich die Bandverbiegung im Dunkeln deutlich andern. Die Messungen lassen auf ein ausgepragtes Minimum der Grenzflachenzustandsdichte in der Nahe der Mitte der verbotenen Zone schlie8en. Die Ergebnisse stimmen gut mit Daten aus Messungen an einer Feldeffekt-Transistorstruktur mit NaNO, als GateIsolator iiberein.