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The support lower bound can fall below PPT distillable entanglement

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QAlgorithms.Papers.Independent.Intakethird100.P90.eta_not_tight

by Gohan · Nov 1, 2026 · Mathlib 0df444a (Lean v4.33.1)

prove2quantum

All systems are finite-dimensional complex Hilbert spaces with fixed orthonormal product bases and positive local dimensions. A state is a positive semidefinite operator of trace one. All logarithms are base two and all operational rates are measured in standard Bell pairs (ebits) per input copy, with deterministic operations and error tending to zero. Write ED,ECE_D,E_CED​,EC​ for distillable entanglement and entanglement cost under completely PPT-preserving CPTP operations; an explicit LOCC subscript denotes unrestricted two-way local operations and classical communication.

Let PaP_aPa​ project onto the three-dimensional antisymmetric subspace of C3⊗C3\mathbb C^3\otimes\mathbb C^3C3⊗C3, and put σa=Pa/3=(I−F)/6\sigma_a=P_a/3=(I-F)/6σa​=Pa​/3=(I−F)/6, where FFF swaps the qutrits. Let EηE_\etaEη​ be the support-sandwich bound of Eq. (4). Then

Eη(σa)=log⁡2(3/2)<ED(σa)=EC(σa)=log⁡2(5/3).E_\eta(\sigma_a)=\log_2(3/2)<E_D(\sigma_a)=E_C(\sigma_a)=\log_2(5/3).Eη​(σa​)=log2​(3/2)<ED​(σa​)=EC​(σa​)=log2​(5/3).

The new evaluation of EηE_\etaEη​ illustrates failure of tightness. The paper explicitly credits the equal operational values to Ref. [12]. This rank-three state is distinct from the rank-two class in the main result.

Preamble
import Definitions.Def_QAlgorithms_Papers_Independent_Intakethird100_P90
Formal statement
noncomputable section

open scoped Matrix ComplexConjugate ComplexOrder

namespace QAlgorithms.Papers.Independent.Intakethird100.P90

attribute [local instance] Classical.propDecidable Classical.decEq

open QAlgorithms

open QAlgorithms.Papers.Independent.Dependency50.P36
  (relativeEntropy rains target canonicalMatrix allowed pptDistillable)

open QAlgorithms.Papers.Independent.Information100.P04 (gamma copies IsPPT)

open QAlgorithms.Papers.Independent.Next46.P42 (regroupProduct)

open QAlgorithms.Papers.Independent.Information100.P06 (supportProjection)

open QAlgorithms.Papers.Independent.Information100.P21 (FiniteLOCC)

open QAlgorithms.Papers.Independent.Gap48.P32 (antisymmetricQutrit)

/-- arXiv:1606.09421v3, PDF p.5, Discussion: the rank-three example.
The new E_eta evaluation is separated in provenance from the operational
value log2(5/3), which this paragraph explicitly credits to Ref.[12]. -/
theorem eta_not_tight :
    etaEntanglement antisymmetricQutrit = Real.logb 2 (3/2 : ℝ) ∧
    (etaEntanglement antisymmetricQutrit : EReal) < pptDistillable antisymmetricQutrit ∧
    pptDistillable antisymmetricQutrit = (Real.logb 2 (5/3 : ℝ) : EReal) ∧
    asymptoticEntanglementCost false antisymmetricQutrit = (Real.logb 2 (5/3 : ℝ) : EReal) := by sorry

end QAlgorithms.Papers.Independent.Intakethird100.P90

end
Source
Irreversibility of Asymptotic Entanglement Manipulation Under Quantum Operations Completely Preserving Positivity of Partial Transpose, arXiv:1606.09421v3, PDF p. 5, Discussion unnumbered example: E_eta can be below PPT distillable entanglement
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What the Lean code literally says, in plain math · gpt-6.1-sol

Let ρ−\rho_-ρ−​ be the matrix on C3⊗C3\mathbb C^3\otimes\mathbb C^3C3⊗C3 whose entries are

(ρ−)(a,b),(c,d)=1(a,b)=(c,d)−1a=d, b=c6.(\rho_-)_{(a,b),(c,d)} =\frac{\mathbf1_{(a,b)=(c,d)}-\mathbf1_{a=d,\ b=c}}6.(ρ−​)(a,b),(c,d)​=61(a,b)=(c,d)​−1a=d, b=c​​.

Write (ΓX)(a,b),(c,d)=X(a,d),(c,b)(\Gamma X)_{(a,b),(c,d)}=X_{(a,d),(c,b)}(ΓX)(a,b),(c,d)​=X(a,d),(c,b)​ and ∥X∥1=Re⁡Tr⁡X†X\|X\|_1=\operatorname{Re}\operatorname{Tr}\sqrt{X^\dagger X}∥X∥1​=ReTrX†X​. Let PρP_\rhoPρ​ be the functional-calculus value at ρ\rhoρ of the scalar function that is zero at zero and one elsewhere, and define Eη(ρ)=−log⁡2η(ρ)E_\eta(\rho)=-\log_2\eta(\rho)Eη​(ρ)=−log2​η(ρ), where η(ρ)\eta(\rho)η(ρ) is the infimum of ∥ΓY∥op\|\Gamma Y\|_{\mathrm{op}}∥ΓY∥op​ over Hermitian YYY satisfying Y−ΓPρ⪰0Y-\Gamma P_\rho\succeq0Y−ΓPρ​⪰0 and Y+ΓPρ⪰0Y+\Gamma P_\rho\succeq0Y+ΓPρ​⪰0. A PPT channel means a map Φ\PhiΦ for which both Φ\PhiΦ and Γ∘Φ∘Γ\Gamma\circ\Phi\circ\GammaΓ∘Φ∘Γ have finite Kraus representations with the sum of Kj†KjK_j^\dagger K_jKj†​Kj​ equal to the identity. Define DPPT(ρ)D_{\mathrm{PPT}}(\rho)DPPT​(ρ) as the extended-real supremum of nonnegative real rrr such that, for every τ>0\tau>0τ>0, all sufficiently large natural nnn admit a PPT channel taking ρ⊗n\rho^{\otimes n}ρ⊗n within trace norm τ\tauτ of Ω⌈2nr⌉\Omega_{\lceil2^{nr}\rceil}Ω⌈2nr⌉​; define CPPT(ρ)C_{\mathrm{PPT}}(\rho)CPPT​(ρ) as the extended-real infimum of nonnegative real rrr such that, for every ε,δ>0\varepsilon,\delta>0ε,δ>0, all sufficiently large positive nnn admit a natural m≤n(r+δ)m\le n(r+\delta)m≤n(r+δ) and a PPT channel taking Ω2m\Omega_{2^m}Ω2m​ within trace norm ε\varepsilonε of ρ⊗n\rho^{\otimes n}ρ⊗n. Here tensor-power basis indices are relabelled by the specified finite-set bijections, and Ωk\Omega_kΩk​ has entry 1/k1/k1/k when both its row and column pairs have equal components, and zero otherwise; m=0m=0m=0 and rate zero are allowed. The assertion is

Eη(ρ−)=log⁡232,Eη(ρ−)<DPPT(ρ−),DPPT(ρ−)=log⁡253,CPPT(ρ−)=log⁡253,E_\eta(\rho_-)=\log_2\frac32,\qquad E_\eta(\rho_-)<D_{\mathrm{PPT}}(\rho_-),\qquad D_{\mathrm{PPT}}(\rho_-)=\log_2\frac53,\qquad C_{\mathrm{PPT}}(\rho_-)=\log_2\frac53,Eη​(ρ−​)=log2​23​,Eη​(ρ−​)<DPPT​(ρ−​),DPPT​(ρ−​)=log2​35​,CPPT​(ρ−​)=log2​35​,

with real values embedded into the extended real numbers where required.

Human review
  • Endorsed by Shuze Chen · Nov 1, 2026

    Confirmed by the moderator at approval.

  • Endorsed by Gohan · Nov 1, 2026

    Confirmed by the mission captain (proposal self-audit).

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