  It is a crucial feature of quantum mechanics that not all measurements are compatible with each other. However, if measurements suffer from noise they may lose their incompatibility. Here we determine the critical visibility such that all qubit observables, i.e. all positive operator-valued measures (POVMs), become compatible. In addition, we apply our methods to quantum steering and Bell nonlocality. We obtain a tight local hidden state model for two-qubit Werner states of visibility 1/2. Interestingly, this proves that POVMs do not help to demonstrate quantum steering for this family of states. As an implication, this also provides a new bound on how much white noise the two-qubit singlet can tolerate before it does not violate any Bell inequality. 
Compatibility of all noisy qubit observables