All star-incompatible measurements can certify steering-based randomness

Abstract

Certifying that quantum randomness generated by untrusted devices is unpredictable to an attacker (say, Eve) is crucial for device-independent security. Bipartite protocols where only one of the parties is trusted are termed one-sided device-independent (1SDI) or steering-based protocols, where the untrusted party (say, Alice) performs measurements on her part of a bipartite entangled state to steer the subsystem of the trusted party (say, Bob) into different ensembles (collectively, an assemblage) of quantum states. Recent work has shown that an assemblage has certified randomness if and only if it is realizable by a set of measurements that are star-incompatible, i.e., the measurement setting of interest for the guessing probability of Eve is incompatible with at least one of the remaining measurement settings of Alice. However, it remains conceivable that there exist star-incompatible measurements that cannot certify steering-based randomness, just like there exist incompatible measurements that cannot certify bipartite Bell nonlocality. Here we prove that any set of star-incompatible measurements can generate steering-based randomness, thereby establishing an equivalence between the two notions. We further introduce a weight-based measure of star-incompatibility and lower bound the amount required to certify a given randomness, capturing the qualitative and quantitative interplay between the quantum resources of star-incompatibility and steering-based randomness.