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.

}, isbn = {2047-7538}, doi = {https://doi.org/10.1038/s41377-020-00385-6}, url = {https://www.nature.com/articles/s41377-020-00385-6}, author = {C. J{\"o}rg and G. Queralt{\'o} and M. Kremer and G. Pelegr{\'\i} and J. Schulz and A. Szameit and G. von Freymann and J. Mompart and V. Ahufinger} } @article {333, title = {Topological state engineering via supersymmetric transformations}, journal = {Communication Physics}, volume = {3}, year = {2020}, chapter = {49}, abstract = {The quest to explore new techniques for the manipulation of topological states simultaneously promotes a deeper understanding of topological physics and is essential in identifying new ways to harness their unique features. Here, we examine the potential of supersymmetric transformations to systematically address, alter and reconfigure the topological properties of a system. To this end, we theoretically and experimentally study the changes that topologically protected states in photonic lattices undergo as supersymmetric\ transformations are applied to their host system. In particular, we show how supersymmetry-induced phase transitions can selectively suspend and re-establish the\ topological protection of specific states. Furthermore, we reveal how understanding the interplay between internal symmetries and the symmetry constraints of supersymmetric transformations provides a roadmap to directly access the desirable topological properties of a system. Our findings pave the way for establishing supersymmetry-inspired techniques as a powerful and versatile tool for topological state engineering.

}, doi = {https://doi.org/10.1038/s42005-020-0316-4}, url = {https://www.nature.com/articles/s42005-020-0316-4$\#$citeas}, author = {G. Queralt{\'o} and M. Kremer and L. J. Maczewsky and M. Heinrich and J. Mompart and V. Ahufinger and A. Szameit} } @article {308, title = {Roadmap on STIRAP applications}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, volume = {52}, number = {20}, year = {2019}, month = {sep}, pages = {202001}, abstract = {STIRAP (stimulated Raman adiabatic passage) is a powerful laser-based method, usually involving two photons, for efficient and selective transfer of populations between quantum states. A particularly interesting feature is the fact that the coupling between the initial and the final quantum states is via an intermediate state, even though the lifetime of the latter can be much shorter than the interaction time with the laser radiation. Nevertheless, spontaneous emission from the intermediate state is prevented by quantum interference. Maintaining the coherence between the initial and final state throughout the transfer process is crucial. STIRAP was initially developed with applications in chemical dynamics in mind. That is why the original paper of 1990 was published in The Journal of Chemical Physics. However, from about the year 2000, the unique capabilities of STIRAP and its robustness with respect to small variations in some experimental parameters stimulated many researchers to apply the scheme to a variety of other fields of physics. The successes of these efforts are documented in this collection of articles. In Part A the experimental success of STIRAP in manipulating or controlling molecules, photons, ions or even quantum systems in a solid-state environment is documented. After a brief introduction to the basic physics of STIRAP, the central role of the method in the formation of ultracold molecules is discussed, followed by a presentation of how precision experiments (measurement of the upper limit of the electric dipole moment of the electron or detecting the consequences of parity violation in chiral molecules) or chemical dynamics studies at ultralow temperatures benefit from STIRAP. Next comes the STIRAP-based control of photons in cavities followed by a group of three contributions which highlight the potential of the STIRAP concept in classical physics by presenting data on the transfer of waves (photonic, magnonic and phononic) between respective waveguides. The works on ions or ion strings discuss options for applications, e.g. in quantum information. Finally, the success of STIRAP in the controlled manipulation of quantum states in solid-state systems, which are usually hostile towards coherent processes, is presented, dealing with data storage in rare-earth ion doped crystals and in nitrogen vacancy (NV) centers or even in superconducting quantum circuits. The works on ions and those involving solid-state systems emphasize the relevance of the results for quantum information protocols. Part B deals with theoretical work, including further concepts relevant to quantum information or invoking STIRAP for the manipulation of matter waves. The subsequent articles discuss the experiments underway to demonstrate the potential of STIRAP for populating otherwise inaccessible high-lying Rydberg states of molecules, or controlling and cooling the translational motion of particles in a molecular beam or the polarization of angular-momentum states. The series of articles concludes with a more speculative application of STIRAP in nuclear physics, which, if suitable radiation fields become available, could lead to spectacular results.

}, doi = {10.1088/1361-6455/ab3995}, url = {https://doi.org/10.1088\%2F1361-6455\%2Fab3995}, author = {K. Bergmann and H. C. N{\"a}gerl and C. Panda and G. Gabrielse and E. Miloglyadov and M. Quack and G. Seyfang and G. Wichmann and S. Ospelkaus and A. Kuhn and S. Longhi and A. Szameit and P. Pirro and B. Hillebrands and X.-F. Zhu and J. Zhu and M. Drewsen and W. K. Hensinger and S. Weidt and T. Halfmann and H.-L. Wang and G. Sorin Paraoanu and N. V. Vitanov and J. Mompart and T. Busch and T. J. Barnum and D. D. Grimes and R. W. Field and M. G. Raizen and E. Narevicius and M. Auzinsh and D. Budker and A. P{\'a}lffy and C. H. Keitel} }