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Free scalar wedge modular geometry — Examples

1 · Prerequisites

2 · Summary

3 · Logical flowchart

4 · Definitions, postulates, theorems and proofs

None yet.

5 · Examples, experiments and counterexamples

ExampleConstruction: AI-generatedVerification: AI-generatedprecheck passverified 2026-10-22 (gpt-6.1-sol)Open item page →

Finite two-mode squeeze illustrates but does not construct wedge factorization

Physical scope

A two-oscillator-mode illustration of a reduced state and its entropy. It is not a construction of the continuum wedge algebra's inside/outside factorization, a thermal density matrix for that algebra, or an experimental observation.

Example

Let HR=HL=ℓ2(N0) with orthonormal number bases {∣n⟩R:n∈N0} and {∣n⟩L:n∈N0}. Use inner products linear in the second variable. For a Hilbert space K, write B(K) for its bounded linear operators, and for u,v∈K write ∣u⟩⟨v∣ for the rank-one operator w↦u⟨v,w⟩. For dimensionless 0<z<1, define ∣ψz⟩=1−z∑n=0∞zn/2∣n⟩R⊗∣n⟩L. Define its left-traced operator ρR by ⟨m∣ρR∣n⟩=∑k=0∞⟨m,k∣ψz⟩⟨n,k∣ψz⟩‾. This coefficient formula defines the partial trace of this rank-one operator over the left oscillator. The vector is normalized, and ρR is a positive diagonal operator with eigenvalues pn=(1−z)zn, whose sum is one. Its entropy in nats, using the natural logarithm, is S(ρR)=−∑n=0∞pnln⁡pn=−ln⁡(1−z)−zln⁡z1−z. This explicitly constructed pair of oscillator modes does not construct a tensor-product factorization of the continuum right-wedge Hilbert space or a density matrix for its local von Neumann algebra.

Diagram: partial trace in the two-mode model

Write Pz=∣ψz⟩⟨ψz∣. Set Vz={cPz:c∈C}⊆B(HR⊗HL) and Wz={cρR:c∈C}⊆B(HR). The rank-one reduction used here is the linear map Rz:Vz→Wz defined by Rz(cPz)=cρR for c∈C; its value on Pz is specified by the product-basis coefficient formula in the Example. The diagram uses χz:C→Vz, χz(c)=cPz, and rz:C→Wz, rz(c)=cρR. The verification shows Rz(Pz)=ρR, so the diagram commutes. Every arrow is defined only on its stated domain; the reduction arrow acts only on scalar multiples of Pz. The TikZ source below specifies that rank-one diagram. Since the library renderer does not execute TikZ, the adjacent array is its rendered algebraic layout. No operation on general trace-class operators or continuum factorization is asserted.

CVzWzÂzrzRz

C→χzVz↘rz↓RzWz

Facts & Assumptions

Given: 0<z<1, the two Hilbert spaces, and their number bases.

[F1]

The shared wedge postulate fixes the continuum scalar Fock model and local right-wedge algebra, and explicitly does not assume a tensor-product factorization across that wedge and its complement. Free scalar wedge data and modular-geometric bridge

Verification

Proof technique: Normalize the explicit series, compute the partial trace in the product basis, and evaluate its convergent entropy series.

Given: [F1] and the data in the Example.

1.1givenalgebra

Let ψz,N=1−z∑n=0Nzn/2∣n⟩R⊗∣n⟩L. Orthogonality gives, for M>N, ∥ψz,M−ψz,N∥2=(1−z)∑n=N+1Mzn≤(1−z)∑n=N+1∞zn=zN+1→0. Thus the partial sums converge in HR⊗HL to ψz. Also (1−z)∑n=0Nzn=1−zN+1, so continuity of the norm gives ⟨ψz∣ψz⟩=(1−z)∑n=0∞zn=1.

2.1givenstep 1.1algebra

The product-basis coefficients are ⟨m,k∣ψz⟩=1−z zk/2δmk. Substitution in the defining partial-trace sum gives ⟨m∣ρR∣n⟩=(1−z)∑k=0∞zkδmkδnk=(1−z)znδmn. Therefore the eigenvalues are exactly pn=(1−z)zn, they are positive, and their sum is one by step 1.1.

3.1givenstep 2.1algebra

Put an=nzn for n≥1. Since an+1/an=z(1+1/n)→z<1, choose q with z<q<1; for all sufficiently large n, an+1≤qan, so an→0 and the tail ∑an is bounded by a geometric series. Differentiating ∑n=0Nzn=(1−zN+1)/(1−z) gives ∑n=1Nnzn−1=(1−(N+1)zN+NzN+1)/(1−z)2. Since NzN→0, taking N→∞ gives ∑n=0∞nzn=z/(1−z)2. Hence ∑n=0∞npn=z/(1−z), and −∑n=0∞pnln⁡pn=−ln⁡(1−z)−(ln⁡z)∑n=0∞npn=−ln⁡(1−z)−zln⁡z/(1−z). The series converges because ∑zn and ∑nzn converge for 0<z<1. In particular, ∑n=0∞pn∣ln⁡pn∣=∣ln⁡(1−z)∣+∣ln⁡z∣ z/(1−z)<∞.

4.1F1step 1.1step 2.1step 3.1givenconstructalgebra∎

Step 2.1 shows that the coefficient formula in the Example gives ρR∣n⟩=pn∣n⟩ with 0<pn<1 and ∑npn=1; hence ρR is bounded and nonzero. Step 1.1 gives Pz≠0. Every element of Vz therefore has a unique form cPz, so Rz(cPz)=cρR defines a linear map from Vz to Wz. On Pz its matrix coefficients are exactly those of the rank-one coefficient formula in the Example; thus Rz(Pz)=ρR and the displayed rank-one diagram commutes. The asserted reduction is confined to this rank-one input. The continuum postulate [F1] instead defines a scalar Fock representation and a right-wedge von Neumann algebra; no map identifying those two constructions is defined or used here. Consequently this example proves the stated oscillator identities but no continuum wedge factorization or density-matrix claim.

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