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No off-diagonal quantum focusing for Rényi divergences
Tanay Kibe, Pratik Roy·July 8, 2026
hep-thgr-qcQuantum Physics
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Abstract
The quantum focusing conjecture is a mathematical expression of the idea that semiclassical gravity remains universally attractive. Its off-diagonal part is a monotonicity condition on the double null shape variation of relative entropy on distinct null generators, and has been argued to follow from strong subadditivity of entanglement entropy. Recent proof of a diagonal Rényi quantum null energy condition raises the question: does a full Rényi focusing statement also hold? We answer this question negatively for any Rényi-type divergence satisfying data processing, tensor additivity, and matched classical--quantum conditioning.