# Measurement-based noiseless linear amplification for quantum communication

## Abstract

Entanglement distillation is an indispensable ingredient in extended quantum communication networks. Distillation protocols are necessarily non-deterministic and require advanced experimental techniques such as noiseless amplification. Recently, it was shown that the benefits of noiseless amplification could be extracted by performing a post-selective filtering of the measurement record to improve the performance of quantum key distribution. We apply this protocol to entanglement degraded by transmission loss of up to the equivalent of 100 km of optical fibre. We measure an effective entangled resource stronger than that achievable by even a maximally entangled resource passively transmitted through the same channel. We also provide a proof-of-principle demonstration of secret key extraction from an otherwise insecure regime. The measurement-based noiseless linear amplifier offers two advantages over its physical counterpart: ease of implementation and near-optimal probability of success. It should provide an effective and versatile tool for a broad class of entanglement-based quantum communication protocols.

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## Acknowledgements

The authors thank S. Rahimi-Keshari, R. Blandino and A. P. Lund for helpful discussions. This research is supported by the Australian Research Council (ARC) under the Centre of Excellence for Quantum Computation and Communication Technology (CE110001027). P.K.L. is an ARC Future Fellow.

## Author information

N.W. and T.C.R. developed the theory. H.M.C., S.M.A., J.J., S.H., T.S. and P.K.L. conceived and conducted the experiment. H.M.C., S.M.A. and N.W. analysed the data. H.M.C., N.W. and S.M.A. drafted the initial manuscript. P.K.L., T.C.R. and T.S. planned and supervised the entire project. All authors discussed the results and commented on the manuscript.

Correspondence to Ping Koy Lam.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary information

Supplementary information (PDF 464 kb)

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Chrzanowski, H., Walk, N., Assad, S. et al. Measurement-based noiseless linear amplification for quantum communication. Nature Photon 8, 333–338 (2014). https://doi.org/10.1038/nphoton.2014.49

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