The efficient separation of the orbital angular momentum (OAM) is essential to both the classical and quantum applications with twisted photons. Here we devise and demonstrate experimentally an efficient method of mimicking the Faraday rotation to sort the OAM based on the OAM-to-polarization coupling effect induced by a modified Mach-Zehnder interferometer. Our device is capable of sorting the OAM of positive and negative numbers, as well as their mixtures. Furthermore, we report the first experimental demonstration to sort optical vortices of noninteger charges. The possibility of working at the photon-count level is also shown using an electron-multiplying CCD camera. Our scheme holds promise for quantum information applications with single-photon entanglement and for high-capacity communication systems with polarization and OAM multiplexing.

We experimentally simulate the spin networks-a fundamental description of quantum spacetime at the Planck level. We achieve this by simulating quantum tetrahedra and their interactions. The tensor product of these quantum tetrahedra comprises spin networks. In this initial attempt to study quantum spacetime by quantum information processing, on a four-qubit nuclear magnetic resonance quantum simulator, we simulate the basic module-comprising five quantum tetrahedra-of the interactions of quantum spacetime. By measuring the geometric properties on the corresponding quantum tetrahedra and simulate their interactions, our experiment serves as the basic module that represents the Feynman diagram vertex in the spin-network formulation of quantum spacetime.

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Based on our constructed robust π/2 mode converter, we report a concise yet high-efficient experiment to realize the detection of both high-order and fractional orbital angular momentum (OAM). The π/2 mode converter that consists of a pair of cylindrical lens is actually not new. However, our experiment shows clearly its excellent robustness, as we have detected the high-order OAM numbers up to ℓ=100 carried by standard Laguerre-Gaussian (LG) modes. The observed patterns of two-dimensional optical lattices indicate that the radial index p of LG beams can be straightforwardly inferred as well. The versatility of the converter is also manifested by input modified LG beams carrying tunable fractional OAM, where we observe the output lattices exhibiting an interesting evolvement from Hermite-Gaussian mode HGm,0 to its adjacent HGm+1,0. Numeric simulations based on OAM eigen-mode decomposition support the experimental results. Our demonstration has potential in both classical and quantum information applications where high OAM modes are needed.