Abstract
Quantum entanglement is a fundamental resource in quantum information processing and its distribution between distant parties is a key challenge in quantum communications. Increasing the dimensionality of entanglement has been shown to improve robustness and channel capacities in secure quantum communications. Here we report on the distribution of genuine high-dimensional entanglement via a 1.2-km-long free-space link across Vienna. We exploit hyperentanglement, that is, simultaneous entanglement in polarization and energy-time bases, to encode quantum information, and observe high-visibility interference for successive correlation measurements in each degree of freedom. These visibilities impose lower bounds on entanglement in each subspace individually and certify four-dimensional entanglement for the hyperentangled system. The high-fidelity transmission of high-dimensional entanglement under real-world atmospheric link conditions represents an important step towards long-distance quantum communications with more complex quantum systems and the implementation of advanced quantum experiments with satellite links.
Highlights
Quantum entanglement is a fundamental resource in quantum information processing and its distribution between distant parties is a key challenge in quantum communications
High-dimensional quantum information can be encoded in various photonic degrees of freedom (DOF), such as transverse orbital angular momentum (OAM)[19,20,21,22], discrete photon arrival time bins[23] or continuous-variable energy–time modes[24,25]
Hyperentanglement has been exploited in the realization of numerous advanced experiments, such as hyperentanglement-assisted Bell-state measurements[3,41,42,43], quantum teleportation of multiple DOF of a single photon[44,45], robust quantum communications with increased channel capacity[46] and efficient entanglement purification schemes[47,48,49]
Summary
Quantum entanglement is a fundamental resource in quantum information processing and its distribution between distant parties is a key challenge in quantum communications. Time-bin qubits[30,31] have been routinely used in fibre-based quantum key distribution systems, which has culminated in the recent demonstration of quantum teleportation over long-distance fibre links[32,33] but have only recently been considered as a viable option for free-space quantum communications in presence of atmospheric turbulence[34,35]. Hyperentanglement has been exploited in the realization of numerous advanced experiments, such as hyperentanglement-assisted Bell-state measurements[3,41,42,43], quantum teleportation of multiple DOF of a single photon[44,45], robust quantum communications with increased channel capacity[46] and efficient entanglement purification schemes[47,48,49]. Experiments that exploit hyperentanglement have not yet ventured beyond the distance limitations of optical tables and protected laboratory environments
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