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A quantum internet is the holy grail of quantum information processing, enabling the deployment of a broad range of quantum technologies and protocols on a global scale. However, numerous challenges must be addressed before the quantum internet can become a reality. Perhaps the most crucial of these is the realization of a quantum repeater, an essential component in the long-distance transmission of quantum information. As the analog of a classical repeater, extender, or booster, the quantum repeater works to overcome loss and noise in the quantum channels constituting a quantum network. Here the conceptual frameworks and architectures for quantum repeaters, as well as the experimental progress toward their realization, are reviewed. Various near-term proposals to overcome the limits to the communication rates set by point-to-point quantum communication are also discussed. Finally, the manner in which quantum repeaters fit within the broader challenge of designing and implementing a quantum internet is overviewed. 

We show that in two dimensional flat torus the number of intersections between random eigenfunctions of general eigenvalues and a given smooth curve is almost exponentially concentrated around its mean, even when the randomness is not gaussian. 

We report the detailed mechanism behind the β to γ phase transformation in Sn-doped and Si-implanted Ga2O3 that we determined based on the direct observation of the atomic scale structure using scanning transmission electron microscopy (STEM). Quantitative analysis of the STEM images revealed that the high concentration of impurity atoms favored the formation of interstitial–divacancy complexes, which then leads to the secondary relaxation that creates additional interstitial atoms and cation vacancies, resulting in a local structure that closely resembles γ-Ga2O3. We explain the mechanism of how the impurity atoms facilitate the transformation, as well as the detailed sequence of the local γ phase transformation. The findings here offer an insight on how the lattice respond to the external stimuli, such as doping and strain, and transform into different structures, which is important for advancing Ga2O3 but also a variety of low symmetry crystals and oxides with multiple polymorphs.