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Finite KMS condition exactly determines the Gibbs density
Statement
Let be a nonzero finite-dimensional complex Hilbert space, let on with energy units J, let have units J s, and let have units J. Write for the ordinary finite-dimensional trace. Assume the finite spectral-calculus and unital C-algebra clauses [A1]–[A2] below. Define the finite-matrix Heisenberg group
A state on the unital C-algebra satisfies the -KMS strip condition of Physical-time KMS strip equilibrium condition for if and only if
Here has units J, has units J, and the physical-time strip has width seconds. The result is finite-dimensional and makes no infinite-volume or relaxation claim.
Facts & Assumptions
Given: , , , , , a state on , and the finite-matrix group .
Finite matrix spectral and state calculus: every finite-dimensional Hermitian matrix has an orthonormal eigenbasis with real eigenvalues, and the finite matrix trace is cyclic. Its current proof correctly normalizes rational-coordinate approximants without claiming the normalized coordinates remain rational; its Step 1 readiness is current. This is authoring readiness, not independent approval.
Finite matrix C-star algebra and density-state duality: for , with its ordinary operator norm is a nonzero unital complex C-algebra. The current finite-matrix carrier is a draft with a complete local proof; no independent acceptance is claimed.
Physical-time KMS strip equilibrium condition: a -KMS state has a bounded continuous function on the closed strip , holomorphic inside, with lower boundary and upper boundary .
Bounded KMS strip norm and zero-edge uniqueness: two bounded continuous functions holomorphic inside the same strip and with the same lower edge agree throughout, including the upper edge.
Finite unitary dynamics and Gibbs KMS identity: for finite self-adjoint , the normalized Gibbs trace state satisfies the finite KMS boundary identity with the physical-time width .
Proof
Given: [A1]–[A2], [F1]–[F3], , , , and .
By [A1]–[A2], choose an orthonormal basis with and ; [A2] puts the finite matrix algebra in the C-dynamical setting required by Physical-time KMS strip equilibrium condition. Let be the matrix unit that maps to and all other basis vectors to zero. Direct multiplication gives , and the exponential action gives for . This formula is used only for finite matrices, where the exponentials and scalar entries are entire.
Fix and apply [F1] to , . Since , the lower boundary of its KMS function is identically zero. By [F2] this KMS function vanishes on the whole strip. Its upper edge at is , so for every off-diagonal matrix unit.
For arbitrary , set and use [F1] with , . The lower edge is . The candidate is entire and bounded on , since and ranges over a compact interval. It has the same lower boundary as the KMS function, so [F2] identifies them. At the upper edge and , the KMS identity is therefore .
The ratios in step 2.2 show that is a constant independent of . Since and , ; the sum is positive and finite, so where . Thus . This also covers and degenerate eigenvalues.
Every has a matrix-unit expansion . By linearity, step 2.1, and step 3.1, . Therefore every finite KMS state is the Gibbs trace state.
Conversely, [F3] supplies the entire bounded finite Gibbs correlation with the stated lower and upper edges, which is exactly [F1]'s finite-matrix KMS condition; [A2] ensures that this KMS definition applies to . The normalized Gibbs trace state is therefore KMS, proving the reverse implication.
Remarks
The matrix-unit ratio proof does not assume that is diagonal or invariant before the KMS condition is used. Equal-energy degeneracies are handled by the same ratio, and step 2.1 removes off-diagonal entries even within a degenerate eigenspace.