Physlib Documentation

Physlib.QuantumMechanics.DDimensions.Operators.Unbounded

Unbounded operators #

i. Overview #

In this module we introduce unbounded operators on inner product spaces. By "unbounded operator" we mean a partially-defined linear map (LinearPMap) which is both densely defined and closable. These provide the mathematical structure appropriate for describing operators in non-relativistic quantum mechanics. Of particular interest are (essentially) self-adjoint unbounded operators since these correspond to physical observables.

Notes #

ii. Key results #

iii. Table of contents #

iv. References #

A. Definitions #

See LinearPMap.instStar and LinearPMap.isSelfAdjoint_def for the definition of IsSelfAdjoint for LinearPMaps.

A LinearPMap U has dense domain iff U.domain is dense in H.

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    A LinearPMap is an unbounded operator iff it has dense domain and is closable.

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      A LinearPMap U is symmetric iff βŸͺU x, y⟫_β„‚ = βŸͺx, U y⟫_β„‚ for all x y : U.domain.

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        A LinearPMap is essentially self-adjoint iff its closure is self-adjoint.

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          B. Dense domain #

          theorem LinearPMap.HasDenseDomain.add_of_le {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {H' : Type u_2} [NormedAddCommGroup H'] [InnerProductSpace β„‚ H'] {U₁ Uβ‚‚ : H β†’β‚—.[β„‚] H'} (h₁ : U₁.HasDenseDomain) (h_le : U₁.domain ≀ Uβ‚‚.domain) :
          (U₁ + Uβ‚‚).HasDenseDomain
          theorem LinearPMap.HasDenseDomain.sub_of_le {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {H' : Type u_2} [NormedAddCommGroup H'] [InnerProductSpace β„‚ H'] {U₁ Uβ‚‚ : H β†’β‚—.[β„‚] H'} (h₁ : U₁.HasDenseDomain) (h_le : U₁.domain ≀ Uβ‚‚.domain) :
          (U₁ - Uβ‚‚).HasDenseDomain

          C. Closability #

          A LinearPMap with densely-defined formal adjoint is closable.

          A zero LinearPMap (any domain) is closable.

          D. Adjoints #

          The adjoint of a zero LinearPMap (any domain) is zero (domain ⊀).

          theorem LinearPMap.adjoint_antitone {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {H' : Type u_2} [NormedAddCommGroup H'] [InnerProductSpace β„‚ H'] {U₁ Uβ‚‚ : H β†’β‚—.[β„‚] H'} [CompleteSpace H] (h₁₂ : U₁.HasDenseDomain ∨ Β¬Uβ‚‚.HasDenseDomain) (h_le : U₁ ≀ Uβ‚‚) :
          Uβ‚‚.adjoint ≀ U₁.adjoint
          theorem LinearPMap.adjoint_add_le_add_adjoint {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {H' : Type u_2} [NormedAddCommGroup H'] [InnerProductSpace β„‚ H'] [CompleteSpace H] (U₁ Uβ‚‚ : H β†’β‚—.[β„‚] H') (h₁₂ : (U₁ + Uβ‚‚).HasDenseDomain) :
          U₁.adjoint + Uβ‚‚.adjoint ≀ (U₁ + Uβ‚‚).adjoint

          E. Symmetric operators #

          theorem LinearPMap.inner_map_polarization {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T : H β†’β‚—.[β„‚] H} (x y : β†₯T.domain) :
          inner β„‚ (↑T y) ↑x = (inner β„‚ (↑T (x + y)) ↑(x + y) - inner β„‚ (↑T (x - y)) ↑(x - y) + Complex.I * inner β„‚ (↑T (x + Complex.I β€’ y)) ↑(x + Complex.I β€’ y) - Complex.I * inner β„‚ (↑T (x - Complex.I β€’ y)) ↑(x - Complex.I β€’ y)) / 4

          The analogue of inner_map_polarization for LinearPMap.

          theorem LinearPMap.inner_map_polarization' {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T : H β†’β‚—.[β„‚] H} (x y : β†₯T.domain) :
          inner β„‚ (↑T x) ↑y = (inner β„‚ (↑T (x + y)) ↑(x + y) - inner β„‚ (↑T (x - y)) ↑(x - y) - Complex.I * inner β„‚ (↑T (x + Complex.I β€’ y)) ↑(x + Complex.I β€’ y) + Complex.I * inner β„‚ (↑T (x - Complex.I β€’ y)) ↑(x - Complex.I β€’ y)) / 4

          The analogue of inner_map_polarization' for LinearPMap.

          theorem LinearPMap.isSymmetric_iff_inner_map_self_real {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T : H β†’β‚—.[β„‚] H} :
          T.IsSymmetric ↔ βˆ€ (x : β†₯T.domain), (starRingEnd β„‚) (inner β„‚ (↑T x) ↑x) = inner β„‚ (↑T x) ↑x
          theorem LinearPMap.IsSymmetric.add {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T₁ Tβ‚‚ : H β†’β‚—.[β„‚] H} (h₁ : T₁.IsSymmetric) (hβ‚‚ : Tβ‚‚.IsSymmetric) :
          (T₁ + Tβ‚‚).IsSymmetric
          theorem LinearPMap.IsSymmetric.sub {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T₁ Tβ‚‚ : H β†’β‚—.[β„‚] H} (h₁ : T₁.IsSymmetric) (hβ‚‚ : Tβ‚‚.IsSymmetric) :
          (T₁ - Tβ‚‚).IsSymmetric
          theorem LinearPMap.IsSymmetric.of_le {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] {T₁ Tβ‚‚ : H β†’β‚—.[β„‚] H} (h₁ : T₁.IsSymmetric) (h_le : Tβ‚‚ ≀ T₁) :
          Tβ‚‚.IsSymmetric

          F. Self-adjoint operators #

          G. Essentially self-adjoint operators #

          The closure is the unique self-adjoint extension of an essentially self-adjoint operator.

          H. Unbounded operators #

          theorem LinearPMap.isUnbounded_of_dense_of_isSymmetric {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] [CompleteSpace H] {E : Submodule β„‚ H} (hE : Dense ↑E) {f : β†₯E β†’β‚—[β„‚] H} (h : βˆ€ (x y : β†₯E), inner β„‚ (f x) ↑y = inner β„‚ (↑x) (f y)) :
          { domain := E, toFun := f }.IsUnbounded

          A LinearPMap constructed from a symmetric LinearMap with dense domain is an unbounded operator.

          theorem LinearPMap.isUnbounded_of_dense_of_isSymmetric' {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace β„‚ H] [CompleteSpace H] {E : Submodule β„‚ H} (hE : Dense ↑E) {f : β†₯E β†’β‚—[β„‚] β†₯E} (h : f.IsSymmetric) :
          { domain := E, toFun := E.subtype βˆ˜β‚— f }.IsUnbounded

          Variant of of_dense_of_isSymmetric for an endomorphism satisfying LinearMap.IsSymmetric.