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 {307, title = {Quantum magnetism with ultracold bosons carrying orbital angular momentum}, journal = {Phys. Rev. A}, volume = {100}, year = {2019}, month = {Aug}, pages = {023615}, doi = {10.1103/PhysRevA.100.023615}, url = {https://link.aps.org/doi/10.1103/PhysRevA.100.023615}, author = {G. Pelegr{\'\i} and J. Mompart and V. Ahufinger and A. J. Daley} } @article {323, title = {Second-order topological corner states with ultracold atoms carrying orbital angular momentum in optical lattices}, journal = {Phys. Rev. B}, volume = {100}, year = {2019}, month = {Nov}, pages = {205109}, abstract = {We propose a realization of a two-dimensional higher-order topological insulator with ultracold atoms loaded into orbital angular momentum (OAM) states of an optical lattice. The symmetries of the OAM states induce relative phases in the tunneling amplitudes that allow to describe the system in terms of two decoupled lattice models. Each of these models displays one-dimensional edge states and zero-dimensional corner states that are correlated with the topological properties of the bulk. We show that the topologically nontrivial regime can be explored in a wide range of experimentally feasible values of the parameters of the physical system. Furthermore, we propose an alternative way to characterize the second-order topological corner states based on the computation of the Zak{\textquoteright}s phases of the bands of first-order edge states.

}, doi = {10.1103/PhysRevB.100.205109}, url = {https://link.aps.org/doi/10.1103/PhysRevB.100.205109}, author = {G. Pelegr{\'\i} and A. M. Marques and V. Ahufinger and J. Mompart and R. G. Dias} } @article {302, title = {Topological edge states and Aharanov-Bohm caging with ultracold atoms carrying orbital angular momentum}, journal = {Phys. Rev. A}, volume = {99}, year = {2019}, month = {Feb}, pages = {023613}, abstract = {We show that bosonic atoms loaded into orbital angular momentum\ l=1\ states of a lattice in a diamond-chain geometry provide a flexible and simple platform for exploring a range of topological effects. This system exhibits robust edge states that persist across the gap-closing points, indicating the absence of a topological transition. We discuss how to perform the topological characterization of the model with a generalization of the Zak{\textquoteright}s phase and we show that this system constitutes a realization of a square-root topological insulator. Furthermore, the relative phases arising naturally in the tunneling amplitudes lead to the appearance of Aharanov-Bohm caging in the lattice. We discuss how these properties can be realized and observed in ongoing experiments.

}, doi = {10.1103/PhysRevA.99.023613}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.023613}, author = {G. Pelegr{\'\i} and A. M. Marques and R. G. Dias and A. J. Daley and J. Mompart and V. Ahufinger} } @article {301, title = {Topological edge states with ultracold atoms carrying orbital angular momentum in a diamond chain}, journal = {Phys. Rev. A}, volume = {99}, year = {2019}, month = {Feb}, pages = {023612}, abstract = {We study the single-particle properties of a system formed by ultracold atoms loaded into the manifold of\ l=1\ orbital angular momentum (OAM) states of an optical lattice with a diamond-chain geometry. Through a series of successive basis rotations, we show that the OAM degree of freedom induces phases in some tunneling amplitudes of the tight-binding model that are equivalent to a net\ π\ flux through the plaquettes. These effects give rise to a topologically nontrivial band structure and protected edge states which persist everywhere in the parameter space of the model, indicating the absence of a topological transition. By taking advantage of these analytical mappings, we also show that this system constitutes a realization of a square-root topological insulator. In addition, we demonstrate that quantum interferences between the different tunneling processes involved in the dynamics may lead to Aharanov-Bohm caging in the system. All these analytical results are confirmed by exact diagonalization numerical calculations.

}, doi = {10.1103/PhysRevA.99.023612}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.023612}, author = {G. Pelegr{\'\i} and A. M. Marques and R. G. Dias and A. J. Daley and V. Ahufinger and J. Mompart} } @article {279, title = {Quantum sensing using imbalanced counter-rotating Bose-Einstein condensate modes}, journal = {New Journal of Physics}, volume = {20}, number = {10}, year = {2018}, pages = {103001}, abstract = {A quantum device for measuring two-body interactions, scalar magnetic fields and rotations is proposed using a Bose-Einstein condensate (BEC) in a ring trap. We consider an imbalanced superposition of orbital angular momentum modes with opposite winding numbers for which a rotating minimal atomic density line appears. We derive an analytical model relating the angular frequency of the minimal density line rotation to the strength of the nonlinear atom-atom interactions and the difference between the populations of the counter-propagating modes. Additionally, we propose a full experimental protocol based on direct fluorescence imaging of the BEC that allows to measure all the quantities involved in the analytical model and use the system for sensing purposes.

}, url = {http://stacks.iop.org/1367-2630/20/i=10/a=103001}, author = {G. Pelegr{\'\i} and J. Mompart and V. Ahufinger} } @article {277, title = {Engineering of orbital angular momentum supermodes in coupled optical waveguides}, journal = {Scientific Reports}, volume = {7}, year = {2017}, month = {APR 26}, pages = {44057}, type = {Article}, abstract = {In this work we demonstrate the existence of orbital angular momentum (OAM) bright and dark supermodes in a three-evanescently coupled cylindrical waveguides system. Bright and dark supermodes are characterized by their coupling and decoupling from one of the waveguides, respectively. In addition, we demonstrate that complex couplings between modes of different waveguides appear naturally due to the characteristic spiral phase-front of OAM modes in two-dimensional configurations where the waveguides are arranged forming a triangle. Finally, by adding dissipation to the waveguide uncoupled to the dark supermode, we are able to filter this supermode out, allowing for the design of OAM mode cloners and inverters.

}, issn = {2045-2322}, doi = {10.1038/srep44057}, author = {A. Turpin and G. Pelegr{\'\i} and J. Polo and J. Mompart and V. Ahufinger} } @article {250, title = {Single-atom edgelike states via quantum interference}, journal = {Phys. Rev. A}, volume = {95}, year = {2017}, month = {Jan}, pages = {013614}, abstract = {We demonstrate how quantum interference may lead to the appearance of robust edgelike states of a single ultracold atom in a two-dimensional optical ribbon. We show that these states can be engineered within the manifold of either local ground states of the sites forming the ribbon or states carrying one unit of angular momentum. In the former case, we show that the implementation of edgelike states can be extended to other geometries, such as tilted square lattices. In the latter case, we suggest using the winding number associated to the angular momentum as a synthetic dimension.

}, doi = {10.1103/PhysRevA.95.013614}, url = {http://link.aps.org/doi/10.1103/PhysRevA.95.013614}, author = {G. Pelegr{\'\i} and J. Polo and A. Turpin and M. Lewenstein and J. Mompart and V. Ahufinger} }