



@article {1994,
	title = {Keyring models: an approach to steerability},
	journal = {Journal of Mathematical Physics},
	volume = {59},
	year = {2018},
	month = {2018/01/02},
	pages = {022103},
	abstract = {<p>If a measurement is made on one half of a bipartite system then, conditioned on the outcome, the other half has a new reduced state. If these reduced states defy classical explanation \&mdash; that is, if shared randomness cannot produce these reduced states for all possible measurements \&mdash; the bipartite state is said to be steerable. Determining which states are steerable is a challenging problem even for low dimensions. In the case of two-qubit systems a criterion is known for T-states (that is, those with maximally mixed marginals) under projective measurements. In the current work we introduce the concept of keyring models \&mdash; a special class of local hidden state model. When the measurements made correspond to real projectors, these allow us to study steerability beyond T-states. Using keyring models, we completely solve the steering problem for real projective measurements when the state arises from mixing a pure two-qubit state with uniform noise. We also give a partial solution in the case when the uniform noise is replaced by independent depolarizing channels. Our results imply that Werner states, which are a special case of the previous states, are unsteerable under real projective measurements if and only if their efficiency is at most 2/π.</p>},
	doi = {10.1063/1.5006199},
	url = {http://aip.scitation.org/doi/full/10.1063/1.5006199},
	author = {Carl Miller and Roger Colbeck and Yaoyun Shi}
}
