Speaker:: Francesco Preti (Forschungszentrum Jülich, Deutchland, host: Tamás Kiss)

Title: Statistical evaluation and optimization of entanglement purification protocols

Date: Tuesday, 18 June  2024, 10.00 

Place: KFKI Camps, Bldg. 1, Conference Room 


We introduce a quantitative characterization of two-qubit entanglement purification protocols based on the amount of entanglement they can retain/destroy. Our approach uses concurrence and the hit-and-run Monte Carlo algorithm applied to the convex set of all two-qubit states. We demonstrate that pioneering protocols are unable to improve the estimated initial average concurrence of almost uniformly sampled density matrices, however, as it is known,they still generate pairs of qubits in a state that is close to a Bell state. We also develop a more efficient protocol and investigate it numerically together with a recent proposal based on an entangling rank-two projector. Furthermore, we present a class of variational purification protocols with continuous parameters and optimize their output concurrence. These optimized algorithms turn out to surpass former proposals and our new protocol by means of not wasting too many entangled states.