Marco Tulio

**MARCO TULIO**The University of Tokyo

Given a general d-dimensional unitary operation Ud for which, apart from the dimension, its description is unknown, is it possible to implement its inverse operation with a universal protocol that works for every unitary Ud? How does the situation change when k uses of unitary operation Ud are allowed? In this talk we show that
any universal protocol implementing the inverse of a general unitary Ud with a positive heralded probability requires at least d−1 uses of Ud. For the cases where k≥d−1 uses are accessible, we construct a parallel and sequential protocol, whose respective probability of failure decreases linearly and exponentially. We then analyse protocols with indefinite causal order. These more general protocols still cannot yield the inverse of a general d-dimensional unitary operation with k

**Seminar, February 14, 2019, 12:00. ICFO’s Seminar Room
Hosted by Antonio Acín**