Approximate quantum Markov property for Gibbs states

Let ρβ\rho_\beta be an arbitrary quantum Gibbs state on a system partitioned as Λ=ABC\Lambda=A\sqcup B\sqcup C, and let dA,Cd_{A,C} denote the distance between AA and CC. Write Iρβ(A:CB){\mathcal I}_{\rho_\beta}(A:C\mid B) for the conditional mutual information. Approximate quantum Markov conjecture. The conditional mutual information rapidly decays with the separation R=dA,CR=d_{A,C}:

Iρβ(A:CB)GI(R).{\mathcal I}_{\rho_\beta}(A:C\mid B)\leq {\mathcal G}_{\mathcal I}(R).

Here GI(R){\mathcal G}_{\mathcal I}(R) is super-polynomially decaying and may depend on β\beta, the regions {A,B,C}\{A,B,C\}, and the fundamental parameters listed in the paper. This conjecture seeks a quantum analogue of the Hammersley--Clifford relation between Markov structure and Gibbs states. It is known for short-range commuting Hamiltonians at arbitrary temperatures, whereas the corresponding exact Markov property fails for non-commuting Hamiltonians; the approximate statement for general quantum Gibbs states remains open.

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Primary source

Tomotaka Kuwahara, “Clustering of conditional mutual information and quantum Markov structure at arbitrary temperatures”, arXiv:2407.05835 (2025).

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