Interpolation conjecture for two-indexed Schatten quasi-norms

Let H1\mathcal{H}_1 and H2\mathcal{H}_2 be Hilbert spaces, and let Sp(H)\mathcal{S}_p(\mathcal{H}) denote the Schatten class of index pp. For θ,r[0,1]\theta,r\in[0,1] and 1q1,p11\leq q_1,p_1\leq\infty, define q,pq,p by

1q=1θr+θq1,1p=1θr+θp1.\frac{1}{q}=\frac{1-\theta}{r}+\frac{\theta}{q_1},\qquad \frac{1}{p}=\frac{1-\theta}{r}+\frac{\theta}{p_1}.

Interpolation conjecture. The quasi-Banach spaces defined in the paper are complex interpolation spaces, completely isometrically, in the sense that

Sq[H1,Sp(H2)]=[Sr(H1H2),Sq1[H1,Sp1(H2)]]θ.\operatorname{\mathcal{S}}_q[\mathcal{H}_1,\operatorname{\mathcal{S}}_p(\mathcal{H}_2)] = \left[\operatorname{\mathcal{S}}_{r}(\mathcal{H}_1\otimes\mathcal{H}_2),\operatorname{\mathcal{S}}_{q_1}[\mathcal{H}_1,\operatorname{\mathcal{S}}_{p_1}(\mathcal{H}_2)]\right]_\theta.

This conjecture extends the known interpolation-scale property of Pisier norms and the interpolation-scale property of Schatten quasi-norms to the two-indexed Schatten quasi-norms introduced in the paper. Its resolution would establish a complex interpolation framework for these quasi-Banach spaces beyond the currently stated results.

Sources & referencesView supporting material

Primary source

Jan Kochanowski, Omar Fawzi and Cambyse Rouzé, “Two-Indexed Schatten Quasi-Norms with Applications to Quantum Information Theory”, arXiv:2604.14055 (2026).

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