One pure steered state implies Einstein-Podolsky-Rosen steering

• URL: http://arxiv.org/abs/2605.18243v1
• Date: Mon, 18 May 2026 11:38:53 GMT
• Title: One pure steered state implies Einstein-Podolsky-Rosen steering
• Abstract summary: We show that a two-qubit entangled state admitting at least one pure steered state is Einstein-Podolsky-Rosen steerable from Alice to Bob.<n>For any two-qubit entangled state, therefore, if one party can steer the other to at least one pure state, the state is two-way EPR steerable.
• Score: 0.42970700836450476
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: In this work, we show that a two-qubit entangled state admitting at least one pure steered state is Einstein-Podolsky-Rosen (EPR) steerable from Alice to Bob. Pure steered states signifies that the quantum steering ellipsoid of Bob is tangent to his Bloch sphere at least at a single point. Furthermore, we prove that for a two-qubit entangled state, Bob's quantum steering ellipsoid is tangent to his Bloch sphere at exactly $N$ points, for $N\in \{ 0,1,2,\infty\}$, if and only if Alice's quantum steering ellipsoid is tangent to her Bloch sphere at exactly $N$ points. For any two-qubit entangled state, therefore, if one party can steer the other to at least one pure state, the state is two-way EPR steerable. We also present several illuminating instances of two-qubit entangled states such that the EPR steering can be verified in terms of pure steered states. Our result addresses the Gisin theorem in a EPR steering scenario: at least a single pure steered state implies two-way steering.

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