TY - JOUR AB - Polaritons with directional in-plane propagation and ultralow losses in van der Waals (vdW) crystals promise unprecedented manipulation of light at the nanoscale. However, these polaritons present a crucial limitation: their directional propagation is intrinsically determined by the crystal structure of the host material, imposing forbidden directions of propagation. Here, we demonstrate that directional polaritons (in-plane hyperbolic phonon polaritons) in a vdW crystal (α-phase molybdenum trioxide) can be directed along forbidden directions by inducing an optical topological transition, which emerges when the slab is placed on a substrate with a given negative permittivity (4H–silicon carbide). By visualizing the transition in real space, we observe exotic polaritonic states between mutually orthogonal hyperbolic regimes, which unveil the topological origin of the transition: a gap opening in the dispersion. This work provides insights into optical topological transitions in vdW crystals, which introduce a route to direct light at the nanoscale. AU - Duan, J. AU - Álvarez-Pérez, G. AU - Voronin, K. V. AU - Prieto Gonzalez, Ivan AU - Taboada-Gutiérrez, J. AU - Volkov, V. S. AU - Martín-Sánchez, J. AU - Nikitin, A. Y. AU - Alonso-González, P. ID - 9334 IS - 14 JF - Science Advances TI - Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition VL - 7 ER - TY - JOUR AB - Phonon polaritons (PhPs)—light coupled to lattice vibrations—with in-plane hyperbolic dispersion exhibit ray-like propagation with large wave vectors and enhanced density of optical states along certain directions on a surface. As such, they have raised a surge of interest, promising unprecedented manipulation of infrared light at the nanoscale in a planar circuitry. Here, we demonstrate focusing of in-plane hyperbolic PhPs propagating along thin slabs of α-MoO3. To that end, we developed metallic nanoantennas of convex geometries for both efficient launching and focusing of the polaritons. The foci obtained exhibit enhanced near-field confinement and absorption compared to foci produced by in-plane isotropic PhPs. Foci sizes as small as λp/4.5 = λ0/50 were achieved (λp is the polariton wavelength and λ0 is the photon wavelength). Focusing of in-plane hyperbolic polaritons introduces a first and most basic building block developing planar polariton optics using in-plane anisotropic van der Waals materials. AU - Martín-Sánchez, Javier AU - Duan, Jiahua AU - Taboada-Gutiérrez, Javier AU - Álvarez-Pérez, Gonzalo AU - Voronin, Kirill V. AU - Prieto Gonzalez, Ivan AU - Ma, Weiliang AU - Bao, Qiaoliang AU - Volkov, Valentyn S. AU - Hillenbrand, Rainer AU - Nikitin, Alexey Y. AU - Alonso-González, Pablo ID - 10177 IS - 41 JF - Science Advances TI - Focusing of in-plane hyperbolic polaritons in van der Waals crystals with tailored infrared nanoantennas VL - 7 ER - TY - JOUR AB - Quantum illumination uses entangled signal-idler photon pairs to boost the detection efficiency of low-reflectivity objects in environments with bright thermal noise. Its advantage is particularly evident at low signal powers, a promising feature for applications such as noninvasive biomedical scanning or low-power short-range radar. Here, we experimentally investigate the concept of quantum illumination at microwave frequencies. We generate entangled fields to illuminate a room-temperature object at a distance of 1 m in a free-space detection setup. We implement a digital phase-conjugate receiver based on linear quadrature measurements that outperforms a symmetric classical noise radar in the same conditions, despite the entanglement-breaking signal path. Starting from experimental data, we also simulate the case of perfect idler photon number detection, which results in a quantum advantage compared with the relative classical benchmark. Our results highlight the opportunities and challenges in the way toward a first room-temperature application of microwave quantum circuits. AU - Barzanjeh, Shabir AU - Pirandola, S. AU - Vitali, D AU - Fink, Johannes M ID - 7910 IS - 19 JF - Science Advances TI - Microwave quantum illumination using a digital receiver VL - 6 ER - TY - JOUR AU - Qi, Chao AU - Minin, Giulio Di AU - Vercellino, Irene AU - Wutz, Anton AU - Korkhov, Volodymyr M. ID - 6919 IS - 9 JF - Science Advances TI - Structural basis of sterol recognition by human hedgehog receptor PTCH1 VL - 5 ER -