Distance-independent rate for entanglement generation in a quantum network

Presenting Author: Ashlesha Patil, University of Arizona
Contributing Author(s): Mihir Pant, Don Towsley and Saikat Guha

Quantum repeaters, built with entangled-photon sources and heralded quantum memories, are connected via lossy links in a network topology. In every time slot, a Bell state is created across each link, among 2 qubits held in memories at either end, with probability p. A node can attempt an n-qubit measurement in a maximally-entangled (e.g., GHZ state) basis, which succeeds with probability q. When n=2, i.e., only Bell-state measurements are used, it was shown: (1) even with local link state (a node knows if its neighbouring links successfully created entanglement in a time slot), end-to-end entanglement rate exceeds routing along the shortest path; (2) but even with global link state information (success-failure outcomes for all links), the rate falls off exponentially with distance, for any. When n >=3, we present protocols for entanglement distribution, and a slightly simpler one for quantum key distribution, that affords a distance-independent rate, using only local link state, in a non-trivial region (i.e., both links and measurements can fail). For the entanglement distribution protocol, the end result is an n-qubit GHZ state between a set of users. When the network topology is a square-grid, for q=1, the threshold for which the above is true, is 0.62. This translates to about 10km of single-mode fiber assuming no other losses. The (p, q) thresholds vary with G and decrease as n increases. Extensions to serving multiple user groups remains ongoing work.

(Session 9b : Sunday from 5:15pm - 5:45pm)


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