Local isometries of bipartite models #
The conclusion of a rigidity theorem moves a strategy along a pair of local isometries: in the
tensor-product model, V_A : ℂ^{d_A} → ℂ^{register} ⊗ ℂ^{H_A} and its partner for the second
player, each player's operator X going to V_A X V_Aᴴ, and the state ψ to
(V_A ⊗ V_B) ψ (MIPRE.Introspection.isometricImage, isometricState). Phase 4 of
planning/mipco-track.md needs the same move in any bipartite model, where there is no
factorization of the space into the two players' parts. What survives is this
(BipartiteModel.LocalIsometry): a linear isometry W of the Hilbert spaces, and for each
player a non-unital ⋆-homomorphism Φ of the player's algebra into the other model's, with
W intertwining the two representations,
π' (πA' (Φ_A a)) ∘ W = W ∘ π (πA a), and likewise for the second player.
X ↦ V_A X V_Aᴴ is exactly such a Φ_A: it is multiplicative because V_Aᴴ V_A = 1, and not
unital, Φ_A 1 = V_A V_Aᴴ being the projection onto the image. In the commuting-operator model
the isometry built from a player's approximate Pauli operators has its entries in that player's
algebra, and conjugation by it is again multiplicative, for the same reason.
- Born probabilities are carried over exactly on the transported state
W ψ(LocalIsometry.bornProb_withState), and so are the players' state norms (LocalIsometry.stateSqNorm_withState). The transported state is a state of the target's Hilbert space but not its state, so the statements are about the target with its state replaced (BipartiteModel.withState). - A projective measurement is carried over to a projective measurement
(
LocalIsometry.transportA):Φ_Aof each element, with the complement1 - Φ_A 1of the image added at one fixed outcome. It is intertwined with the original byW(LocalIsometry.intertwine_transportA), so a strategy and its transport have the same value on the transported state (LocalIsometry.povmValue_transport). This isMIPRE.Introspection.isometricPOVMin any model. - Local isometries compose (
LocalIsometry.comp), and exchange with the players (LocalIsometry.swap).
Replacing the state #
The state model with its state replaced by the vector φ of its Hilbert space.
Equations
- M.withState φ = { H := M.H, normedAddCommGroup := M.normedAddCommGroup, innerProductSpace := M.innerProductSpace, completeSpace := ⋯, ψ := φ, π := M.π }
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The bipartite model with its state replaced by the vector φ of its Hilbert space.
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Pushing a measurement forward along a unital ⋆-homomorphism #
The image of a projective measurement under a ⋆-homomorphism preserving the unit.
A POVM pushed forward along a ⋆-homomorphism preserving the unit.
Equations
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A projective measurement, as a POVM: its elements are nonnegative, being star projections.
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Local isometries #
A local isometry from the bipartite model M into the bipartite model M': a linear
isometry W of the Hilbert spaces, and for each player a non-unital ⋆-homomorphism of the
player's algebra into the other model's, the two representations intertwined by W. The states
play no part: how far W ψ is from the state of M' is the error of whatever produced the
isometry.
The isometry of the Hilbert spaces.
The first player's operators, moved along the isometry.
The second player's operators, moved along the isometry.
The isometry intertwines the first player's operators with their images.
The isometry intertwines the second player's operators with their images.
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The local isometry with the players exchanged.
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Local isometries compose.
Equations
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The inverse of a local isometry with an inverse isometry and inverse homomorphisms.
Equations
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The isometry intertwines a product of the two players' operators with the product of their images.
The image of the unit of the first player's algebra fixes the image of the isometry.
Born probabilities are carried over exactly, on the transported state.
The first player's state norms are carried over exactly, on the transported state.
The transported state has the norm of the state.
An isometry carrying the state to the state #
The local isometries between extensions of one model by registers carry the state exactly, and then every quantity computed from the state is carried over.
The cross norm ‖(πA a - πB b) ψ‖ is carried over.
The image of the unit #
The complement of the image of the first player's unit.
The complement of the image of the unit kills the image of the isometry.
Transporting a projective measurement #
The transport of a family of the first player's operators: the image of each, with the
complement of the image of the unit added at the outcome x₀.
Instances For
The transport of a projective measurement is a projective measurement.
The transport is intertwined with the original by the isometry.
The transport of a projective measurement, as a POVM of the target's first player.
Equations
- Φ.transportA x₀ P hP = { mats := fun (x : X) => ⟨Φ.transportOpA x₀ P.op x, ⋯⟩, nonneg := ⋯, normalized := ⋯ }
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The transport of a projective measurement of the second player.
Equations
- Φ.transportB y₀ Q hQ = Φ.swap.transportA y₀ Q hQ
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The value of a transported strategy #
The Born probabilities of a transported pair of measurements are the original ones, on the transported state.
A strategy and its transport have the same value, on the transported state.
The value of a strategy moved along a unital local isometry #
A strategy moved along a local isometry preserving the units has its value, on the transported state.
The same, for a local isometry carrying the state to the state.