Extension of the trace-representation formula for quantum Hellinger divergences

Let ρ\rho and σ\sigma be the states appearing in the definition of the quantum Hellinger divergence Hα(ρ∥σ)H_\alpha(\rho\|\sigma), and let α>1\alpha>1. Trace-representation conjecture. For any α>1\alpha>1,

Hα(ρ∥σ)=∫0∞Tr⁡(ρ(σ+s\mathds1)−1)α ds−1α−1.H_\alpha(\rho\|\sigma)=\int_0^\infty \operatorname{Tr}\left(\rho(\sigma+s\mathds{1})^{-1}\right)^\alpha\,\mathrm{d}s-\frac{1}{\alpha-1}.

The paper proves this formula for integer α≥2\alpha\geq2; the conjecture extends that result to all real α>1\alpha>1.

References

Primary source

Salman Beigi, Christoph Hirche and Marco Tomamichel, “Some properties and applications of the new quantum f-divergences”, arXiv:2501.03799 (2025).

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