Distributing entanglement without actually sending it

• Post by: admin
• April 8, 2014
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We have a new PRL paper online, where we demonstrate that two parties can establish entanglement between their labs without directly communicating any entanglement between them. Physical Review Letters was kind enough to honor our work with an Editor’s Suggestion and an accompanying Physics Viewpoint written by Christine Silberhorn—a big thanks to the Physics editors and to Christine!

The idea goes back to a paper by Toby ‘Qubit’ Cubitt and co-authors, but it took a decade for people to figure our that the resource that allows Alice and Bob to achieve this task is—at least to some degree—quantum discord. This was elaborated in a series of theory papers by Streltsov et al., Alastair Kay, and our collaborators in Singapore. The protocol works as follows. Alice and Bob have separate quantum systems that they want to entangle. Alice starts by doing some local (in respect to her lab) encoding between her system and a carrier, and then sends Bob this carrier. Bob does some local decoding and Alice and Bob’s systems end up being entangled. Importantly, this can be achieved without ever entangling the carrier with either Alice’s or Bob’s system.

This is not only really cute from a foundational point of view it also has practical applications. In our paper, we describe scenarios in which at certain noise levels—either in the systems themselves, or in the channel—entanglement distribution with separable carriers works better than the alternative of direct entanglement sharing. So the protocol could indeed be useful in future quantum networks.

For more information, I recommend reading Christine’s viewpoint, or Margherita’s writeup for the popular science website 2physics.