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Fully characterizing the steerability of a quantum state of a bipartite system has remained an open problem since the concept of steerability was defined. In this talk, we discuss a geometric approach to steerability and suggest a necessary and sufficient condition for a two-qubit state to be steerable with respect to projective measurements. To this end, we define the critical radius of local models and show that a state of two qubits is steerable with respect to projective measurements from Alice's side if and only if her critical radius of local models is less than 1. We then calculate the critical radius of local models for the so-called T-states by proving the optimality of a recently suggested local hidden state model.

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Chau Nguyen, MPI Dresden
Seminarroom 0.02, ETP
Contact: David Gross