Isomorphisms of bipartite models #
A local isometry (BipartiteModel.LocalIsometry) moves a strategy from one model into another,
and carries its value over on the transported state. When the isometry is onto, the two
homomorphisms are bijective and the state goes to the state, nothing is lost in either direction:
the two models are isomorphic (BipartiteModel.Iso), and a property of models stated through
Born probabilities --- the soundness of a test, the domination of the strategies by a value ---
passes from either to the other. The constructions of MIPRE/Foundations/AncillaIsometry.lean
and MIPRE/Foundations/TensorExpand.lean are isomorphisms in this sense, once their state
hypotheses hold:
- an extension by one-point registers in the state
1is the model itself (BipartiteModel.expandUnit); - associativity of extensions (
BipartiteModel.assocIso), relabelling of the registers (BipartiteModel.relabelIso), and the exchange of the players in an extension (BipartiteModel.swapExpandIso); - an isomorphism of models extends to their extensions by the same registers
(
BipartiteModel.Iso.expandCongr); - the extension of a tensor-product model is the tensor-product model of the expanded vector
(
BipartiteModel.tensorExpandIso), and a tensor-product model is unchanged by relabelling the two factors (BipartiteModel.tensorReindexIso), so that a statement about the tensor-product models of states onFin a × Fin bholds on any finite factors.
Each of these is a local isometry of those files with inverses (Iso.ofLocalIsometry), and every
isomorphism is a local isometry (Iso.toLocalIsometry), so the lemmas about local isometries
carrying the state to the state apply. What an isomorphism carries over, exactly: Born
probabilities (Iso.bornProb_eq), the players' state norms (Iso.stateSqNorm_eq), the value of a
family of measurements and of a projective strategy pushed forward (Iso.povmValue_push,
Iso.value_pushStrat, and so the domination of a model by a value, Iso.dominates), and the
inconsistency of two families (Iso.inconsistency_eq). The exchange of the players is an
operation on projective strategies too (ProjStrat.swap), which keeps the value of a game that is
symmetric in the players, and on inconsistencies (BipartiteModel.inconsistency_swap).
A one-point ℓ² sum, exchanged registers, and three ⋆-algebra isomorphisms of matrices #
The ℓ² sum over a one-point index {i₀} is the space itself.
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- One or more equations did not get rendered due to their size.
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Isomorphisms #
An isomorphism of bipartite models: a unitary of the Hilbert spaces carrying the state of
M to the state of M', and a ⋆-algebra isomorphism for each player, the two representations
intertwined by the unitary. Everything a model computes from its state and its players' operators
--- Born probabilities, state norms, values, inconsistencies --- is carried across unchanged.
The unitary of the Hilbert spaces.
The first player's algebras.
The second player's algebras.
The unitary intertwines the first player's operators with their images.
The unitary intertwines the second player's operators with their images.
The unitary carries the state to the state.
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The identity isomorphism.
Equations
- MIPRE.BipartiteModel.Iso.refl M = { W := LinearIsometryEquiv.refl ℂ M.H, ΦA := StarAlgEquiv.refl ℂ 𝒜, ΦB := StarAlgEquiv.refl ℂ ℬ, intertwineA := ⋯, intertwineB := ⋯, W_ψ := ⋯ }
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The inverse isomorphism.
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Isomorphisms compose, the first applied first.
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The isomorphism with the players exchanged.
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An isomorphism is a local isometry, its homomorphisms unital and its isometry carrying the
state to the state (toLocalIsometry_W_ψ).
Equations
- Φ.toLocalIsometry = { W := Φ.W.toLinearIsometry, ΦA := Φ.ΦA.toNonUnitalStarAlgHom, ΦB := Φ.ΦB.toNonUnitalStarAlgHom, intertwineA := ⋯, intertwineB := ⋯ }
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A local isometry with inverses is an isomorphism: an isometry with a right inverse, and homomorphisms with two-sided inverses, carrying the state to the state.
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What an isomorphism carries over #
Born probabilities are carried over.
The first player's state norms are carried over.
The second player's state norms are carried over.
The cross norms are carried over.
The state has the norm of the state.
Measurements and strategies moved along an isomorphism #
A POVM of the first player, moved along the isomorphism.
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- Φ.pushA P = MIPRE.POVMIn.pushforward Φ.toLocalIsometry.ΦA ⋯ P
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A POVM of the second player, moved along the isomorphism.
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- Φ.pushB Q = MIPRE.POVMIn.pushforward Φ.toLocalIsometry.ΦB ⋯ Q
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Two families of measurements whose operators correspond have the same value.
A family of measurements moved along the isomorphism has its value.
A projective strategy moved along the isomorphism: each measurement pushed forward.
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A projective strategy moved along the isomorphism has its value.
A value model dominating a model dominates every model isomorphic to it: a projective strategy moves along the isomorphism with its value.
Two pairs of families whose operators correspond have the same inconsistency.
Two families moved along the isomorphism have their inconsistency.
Exchanging the players in a strategy and in an inconsistency #
A projective strategy with the players exchanged, as a strategy of the swapped model for
any game G' of the exchanged shape: the first player's measurements are the second's.
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The exchanged strategy has the value of the strategy, for a game G' that is G with the
players exchanged: the question pair (y, x) weighed as (x, y), and the answers (b, a)
accepted as (a, b). For a game symmetric in the players, G' is G itself.
The inconsistency is symmetric in the players: with the players exchanged, the second player's family is measured first.
Isomorphisms between ancilla extensions #
An extension by one-point registers in the state 1 is the model itself: the one-by-one
matrices over each player's algebra are that algebra.
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Associativity, as an isomorphism: the extension in e' of the extension in e is the
extension by the product registers, in the product vector e'' (BipartiteModel.assoc).
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- One or more equations did not get rendered due to their size.
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The exchange of the players, as an isomorphism: the exchanged extension in e is the
extension of the exchanged model in the exchanged vector (BipartiteModel.swapExpand).
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- One or more equations did not get rendered due to their size.
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A relabelling of the registers, as an isomorphism, along bijections f and g, from the
extension in e to the extension in the relabelled vector e' (BipartiteModel.relabel).
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The unitary of an isomorphism, acting on each component of an ℓ² sum.
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- Φ.expandCongrW e = (M.ampl e).trans ((LinearIsometryEquiv.piLpCongrRight 2 fun (x : α × β) => Φ.W).trans (M'.ampl e).symm)
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An isomorphism extends to the extensions by the same registers in the same state: the unitary acts on each component, and each player's isomorphism entrywise.
Equations
- Φ.expandCongr e = { W := Φ.expandCongrW e, ΦA := MIPRE.mapMatrixStarAlgEquiv Φ.ΦA, ΦB := MIPRE.mapMatrixStarAlgEquiv Φ.ΦB, intertwineA := ⋯, intertwineB := ⋯, W_ψ := ⋯ }
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Isomorphisms of tensor-product models #
The extension of a tensor-product model is the tensor-product model of the expanded vector,
as an isomorphism (BipartiteModel.tensorExpand, inverted by tensorUnexpand).
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The unitary of ℂ^{dA × dB} onto ℂ^{dA' × dB'} relabelling the two factors.
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A tensor-product model is unchanged by relabelling its two factors: along bijections
f : dA ≃ dA' and g : dB ≃ dB', the model of ψ is the model of ψ relabelled, each player's
matrices relabelled along their factor.
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