Quantum communication is based on the generation of quantum states and exploitation of quantum resources for communication protocols. Currently, photons are considered as the optimal carrier of information, because they enable long-distance transition with resilience to decoherence, and they are relatively easy to create and detect. Entanglement is a fundamental resource for quantum communication and information processing, and it is of particular importance for quantum repeaters [1]. Hyperentanglement [2], a state where parties are entangled with two or more degrees of freedom (DoFs), provides an important additional resource because it increases data rates and enhances error resilience. However, in photonics, the channel capacity, i.e. the ultimate throughput, is fundamentally limited when dealing with linear elements. We propose a technique for achieving higher transmission rates for quantum communication by using hyperentangled states, based on multiplexing multiple DoFs on a single photon, transmitting the photon, and eventually demultiplexing the DoFs to different photons at the destination, using a Bell state measurement. Following our scheme, one can generate two entangled qubit pairs by sending only a single photon. The proposed transmission scheme lays the groundwork for novel quantum communication protocols with higher transmission rate and refined control over scalable quantum technologies.

Photonic quantum computing has been rapidly advancing over the past decade, with measurement-based approaches emerging as particularly promising. A crucial requirement for these approaches is the generation of large-scale cluster states. In this work, we present a method to create cluster states using Photonic Time-Crystals (PTCs) — dielectric materials with their refractive index rapidly modulated in time. PTCs effectively function as a set of optical parametric oscillators and beam-splitters, producing simultaneous two-mode squeezing for many pairs of photonic modes with opposite wavevectors. We utilize this capability to propose a method for generating two-dimensional cluster states, offering important advantages over existing protocols.

We propose metasurfaces-based scheme to expand the polarization entanglement between two photons. Our approach increases the entanglement dimension, expanding the biphoton state into a hyperentangled state with polarization and OAM entanglement imprinted onto two photons.

We present a method to protect the entanglement of a Bell-state encoded on a single photon performing a two-dimensional discrete-time quantum walk. We find an edge-state at the boundary of two distinct quantum walk domains.

We present a technique for generating a two-dimensional cluster state, with a graphene topology. We exploit hyperentangled states, delay loops, and geometrical phase masks that act as beam splitters for different degrees of freedom.

We study light propagation of electromagnetic waves in a medium with a homogeneous refractive index varying quasi-periodically in time. We study two types of time-varying quasi-crystals: Andrey Aubrey and Fibonacci sequence.

We present a topological structure performing a self-cleaning effect in synthetic space, controlled by a homogeneous gain medium in real space, producing a ground-state in both synthetic space and real space.