Ultra-long quantum walks via spin-orbit photonics

The possibility of fine-tuning the couplings between optical modes is a key requirement in photonic circuits for quantum simulations. In these architectures, emulating the long-time evolution of particles across large lattices requires sophisticated setups that are often intrinsically lossy. Here we report ultra-long photonic quantum walks across several hundred optical modes, obtained by propagating a light beam through very few closely stacked liquid-crystal meta-surfaces. By exploiting spin-orbit effects, these implement space-dependent polarization transformations that mix circularly polarized optical modes carrying quantized transverse momentum. As each metasurface implements long-range couplings between distant modes, by using only a few of themwe simulate quantum walks up to 320 discrete steps without any optical amplification, far beyond state-of-the-art experiments. To showcase the potential of this method, we experimentally demonstrate that in the long time limit a quantum walk affected by dynamical disorder generates maximal entanglement between two system partitions. Our platform grants experimental access to large-scale unitary evolutions while keeping optical losses at a minimum, thereby paving the way to massive multi-photon multi-mode quantum simulations. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

In this work, a method of photonic quantum walks using liquid-crystal meta-surfaces is reported, enabling ultra-long distance walks between hundreds of optical modes. By exploiting spin-orbit effects, this method allows for space-dependent polarization transformations and mixing of circularly polarized optical modes with quantized transverse momentum. By using only a few meta-surfaces, quantum walks up to 320 discrete steps are simulated without optical amplification, surpassing current state-of-the-art experiments. Rating: 9 points.