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Equation 19 · Part 1 · The Entry a Relabeling Cannot Write

Symbol Lambda^dagger

Λ†(Ic)=If\Lambda^\dagger(I_c) = I_f
Λ†\Lambda^\dagger

What this part means

the define.

Its job in the formula

Lambdada^dagger is part of the quantity the equation computes from the expression on the right.

Where the article explains it

Define Λ†\Lambda^\dagger: B(Hc)\mathcal B(\mathcal H_c) →\to B(Hf)\mathcal B(\mathcal H_f) by the pairing that must hold for every fine state and every coarse observable OcO_c , Tr\mathrm{Tr}[\big[Λ(ρ)\Lambda(\rho)\,OcO_c]\big] = Tr\mathrm{Tr}[\big[ρ\rho\,Λ†(Oc)\Lambda^\dagger(O_c)]\big].

The passage around this formula

Λ†\Lambda^\dagger is positive because Λ\Lambda is completely positive and every Λ(ρ)\Lambda(\rho) with ρ\rho ≥\ge 0 is itself a valid state; it is unital, Λ†(Ic)\Lambda^\dagger(I_c) = IfI_f , because Λ\Lambda preserves trace for every input. This duality is the same construction Stinespring used to show that any completely positive map admits a dilation to a larger, unitary description [ 9 ] , and it lets a coarse Hamiltonian be pulled back onto the fine space without the fine space’s own structure ever being disturbed.

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Learn the underlying idea

An exponent tells how a base is used in multiplication. In x³, x is the base and 3 is the exponent: x³ = x × x × x.

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Sources cited in the surrounding passage

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