Entanglement distillation, the purpose of which is to probabilistically increase the strength and purity of quantum entanglement, is a primary element of many quantum communication and computation protocols. It is particularly necessary in quantum repeaters in order to counter the degradation of entanglement that inevitably occurs due to losses in communication lines. Here, we distil the Einstein–Podolsky–Rosen state of light, the workhorse of continuous-variable entanglement, using noiseless amplification. The advantage of our technique is that it permits recovering a macroscopic level of entanglement, however low the initial entanglement or however high the loss may be. Experimentally, we recover the original entanglement level after one of the Einstein–Podolsky–Rosen modes has experienced a loss factor of 20. The level of entanglement in our distilled state is higher than that achievable by direct transmission of any state through a similar loss channel. This is a key step towards realizing practical continuous-variable quantum communication protocols.
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The authors thank G. Adesso for discussions and the Russian Quantum Center for support. A.L. is supported by the National Science and Engineering Research Council of Canada and is a fellow of the Canadian Institute for Advanced Research. T.C.R.'s research is funded by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project no. CE110001027).
The authors declare no competing financial interests.
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Ulanov, A., Fedorov, I., Pushkina, A. et al. Undoing the effect of loss on quantum entanglement. Nature Photon 9, 764–768 (2015). https://doi.org/10.1038/nphoton.2015.195
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