Entanglement purification by counting and locating errors with entangling measurements

Understand

We consider entanglement purification protocols for multiple copies of qubit states.

• We use high-dimensional auxiliary entangled systems to learn about number and positions of errors in the noisy ensemble in an explicit and controlled way, thereby reducing the amount of noise in the ensemble and purifying the remaining states.
• This allows us to design entanglement purification protocols for any number of copies that work particularly well for a small number of expected errors, i.e.
• high fidelity of initial states.