Implement a bases api and rework abstract types

CHANGELOG.md

@@ -1,5 +1,11 @@
 # News
 
+## v0.4.0 - 2024-11-26
+
+- Add `OperatorBasis` and `SuperOperatorBasis` along with correspond `fullbasis` function to obtain these from corresponding instances of these objects.
+- Change type parameters for `StateVector`, `AbstractKet` `AbstractBra` `AbstractOperator` `AbstractSuperOperator` to elimitate datatype parameter and enforce them carrying their respective `Basis`, `OperatorBasis`, or `SuperOperatorBasis`.
+
+
 ## v0.3.6 - 2024-09-08
 
 - Add `coherentstate`, `thermalstate`, `displace`, `squeeze`, `wigner`, previously from QuantumOptics.

Project.toml

@@ -1,7 +1,7 @@
 name = "QuantumInterface"
 uuid = "5717a53b-5d69-4fa3-b976-0bf2f97ca1e5"
 authors = ["QuantumInterface.jl contributors"]
-version = "0.3.6"
+version = "0.4.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/abstract_types.jl

@@ -1,54 +1,54 @@
 """
-Abstract base class for `Bra` and `Ket` states.
+Abstract type for `Bra` and `Ket` states.
 
-The state vector class stores the coefficients of an abstract state
-in respect to a certain basis. These coefficients are stored in the
-`data` field and the basis is defined in the `basis`
-field.
+The state vector type stores an abstract state with respect to a certain
+Hilbert space basis.
+All deriving types must define the `fullbasis` function which
+returns the state vector's underlying `Basis`.
 """
-abstract type StateVector{B,T} end
-abstract type AbstractKet{B,T} <: StateVector{B,T} end
-abstract type AbstractBra{B,T} <: StateVector{B,T} end
+abstract type StateVector{B<:Basis} end
+abstract type AbstractKet{B} <: StateVector{B} end
+abstract type AbstractBra{B} <: StateVector{B} end
 
 """
-Abstract base class for all operators.
+Abstract type for all operators which represent linear maps between two
+Hilbert spaces with respect to a given basis in each space.
 
-All deriving operator classes have to define the fields
-`basis_l` and `basis_r` defining the left and right side bases.
+All deriving operator types must define the `fullbasis` function which
+returns the operator's underlying `OperatorBasis`.
 
 For fast time evolution also at least the function
 `mul!(result::Ket,op::AbstractOperator,x::Ket,alpha,beta)` should be
 implemented. Many other generic multiplication functions can be defined in
 terms of this function and are provided automatically.
+
+See [TODO: reference operators.md in docs]
 """
-abstract type AbstractOperator{BL,BR} end
+abstract type AbstractOperator{B<:OperatorBasis} end
 
 """
-Base class for all super operator classes.
-
-Super operators are bijective mappings from operators given in one specific
-basis to operators, possibly given in respect to another, different basis.
-To embed super operators in an algebraic framework they are defined with a
-left hand basis `basis_l` and a right hand basis `basis_r` where each of
-them again consists of a left and right hand basis.
-```math
-A_{bl_1,bl_2} = S_{(bl_1,bl_2) ↔ (br_1,br_2)} B_{br_1,br_2}
-\\\\
-A_{br_1,br_2} = B_{bl_1,bl_2} S_{(bl_1,bl_2) ↔ (br_1,br_2)}
+Abstract type for all super-operators which represent linear maps between two
+operator spaces with respect to a given basis for each space.
+
+All deriving operator types must define the `fullbasis` function which
+returns the operator's underlying `SuperOperatorBasis`.
+
+See [TODO: reference superoperators.md in docs]
 ```
 """
-abstract type AbstractSuperOperator{B1,B2} end
+abstract type AbstractSuperOperator{B<:SuperOperatorBasis} end
 
 function summary(stream::IO, x::AbstractOperator)
-    print(stream, "$(typeof(x).name.name)(dim=$(length(x.basis_l))x$(length(x.basis_r)))\n")
-    if samebases(x)
+    b = fullbasis(x)
+    print(stream, "$(typeof(x).name.name)(dim=$(length(b.left))x$(length(b.right)))\n")
+    if samebases(b)
         print(stream, "  basis: ")
-        show(stream, basis(x))
+        show(stream, basis(b))
     else
         print(stream, "  basis left:  ")
-        show(stream, x.basis_l)
+        show(stream, b.left)
         print(stream, "\n  basis right: ")
-        show(stream, x.basis_r)
+        show(stream, b.right)
     end
 end
 

src/bases.jl

@@ -1,9 +1,9 @@
 """
-Abstract base class for all specialized bases.
+Abstract type for all specialized bases.
 
-The Basis class is meant to specify a basis of the Hilbert space of the
-studied system. Besides basis specific information all subclasses must
-implement a shape variable which indicates the dimension of the used
+The `Basis` type is meant to specify a basis of the Hilbert space of the
+studied system. Besides basis specific information, all concrete subtypes must
+implement a shape field which indicates the dimension of the used
 Hilbert space. For a spin-1/2 Hilbert space this would be the
 vector `[2]`. A system composed of two spins would then have a
 shape vector `[2 2]`.
@@ -13,6 +13,26 @@ class.
 """
 abstract type Basis end
 
+"""
+Parametric composite type for all operator bases.
+
+See [TODO: reference operators.md in docs]
+"""
+struct OperatorBasis{BL<:Basis,BR<:Basis}
+    left::BL
+    right::BR
+end
+
+"""
+Parametric composite type for all superoperator bases.
+
+See [TODO: reference superoperators.md in docs]
+"""
+struct SuperOperatorBasis{BL<:OperatorBasis,BR<:OperatorBasis}
+    left::BL
+    right::BR
+end
+
 """
     length(b::Basis)
 
@@ -25,11 +45,24 @@ Base.length(b::Basis) = prod(b.shape)
 
 Return the basis of an object.
 
-If it's ambiguous, e.g. if an operator has a different left and right basis,
-an [`IncompatibleBases`](@ref) error is thrown.
+If it's ambiguous, e.g. if an operator or superoperator has a different
+left and right basis, an [`IncompatibleBases`](@ref) error is thrown.
 """
 function basis end
 
+basis(b::OperatorBasis) = (check_samebases(b); b.left)
+basis(b::SuperOperatorBasis) = (check_samebases(b); b.left.left)
+
+"""
+    fullbasis(a)
+
+
+Returns B where B<:Basis when typeof(a)<:StateVector.
+Returns B where B<:OperatorBasis when typeof(a)<:AbstractOperator.
+Returns B where B<:SuperOperatorBasis for typeof(a)<:AbstractSuperOperator.
+"""
+function fullbasis end
+
 
 """
     GenericBasis(N)
@@ -80,13 +113,11 @@ contains another CompositeBasis.
 tensor(b1::Basis, b2::Basis) = CompositeBasis([length(b1); length(b2)], (b1, b2))
 tensor(b1::CompositeBasis, b2::CompositeBasis) = CompositeBasis([b1.shape; b2.shape], (b1.bases..., b2.bases...))
 function tensor(b1::CompositeBasis, b2::Basis)
-    N = length(b1.bases)
     shape = vcat(b1.shape, length(b2))
     bases = (b1.bases..., b2)
     CompositeBasis(shape, bases)
 end
 function tensor(b1::Basis, b2::CompositeBasis)
-    N = length(b2.bases)
     shape = vcat(length(b1), b2.shape)
     bases = (b1, b2.bases...)
     CompositeBasis(shape, bases)
@@ -160,24 +191,35 @@ macro samebases(ex)
 end
 
 """
+    samebases(a)
     samebases(a, b)
 
-Test if two objects have the same bases.
+Test if one object has the same left and right bases or
+if two objects have the same bases
 """
-samebases(b1::Basis, b2::Basis) = b1==b2
-samebases(b1::Tuple{Basis, Basis}, b2::Tuple{Basis, Basis}) = b1==b2 # for checking superoperators
+samebases(b1::Basis, b2::Basis) = (b1 == b2)
+samebases(b::OperatorBasis) = (b.left == b.right)
+samebases(b1::OperatorBasis, b2::OperatorBasis) = ((b1.left == b2.left) && (b1.right == b2.right))
+samebases(b::SuperOperatorBasis) = samebases(b.left, b.right)
+samebases(b1::SuperOperatorBasis, b2::SuperOperatorBasis) = (samebases(b1.left, b2.left) && samebases(b1.right, b2.right))
 
 """
+    check_samebases(a)
     check_samebases(a, b)
 
-Throw an [`IncompatibleBases`](@ref) error if the objects don't have
-the same bases.
+Throw an [`IncompatibleBases`](@ref) error if the two objects don't have
+the same bases or the one object doesn't have the same left and right bases.
 """
 function check_samebases(b1, b2)
     if BASES_CHECK[] && !samebases(b1, b2)
         throw(IncompatibleBases())
     end
 end
+function check_samebases(b)
+    if BASES_CHECK[] && !samebases(b)
+        throw(IncompatibleBases())
+    end
+end
 
 
 """

src/expect_variance.jl

@@ -3,33 +3,34 @@
 
 If an `index` is given, it assumes that `op` is defined in the subsystem specified by this number.
 """
-function expect(indices, op::AbstractOperator{B1,B2}, state::AbstractOperator{B3,B3}) where {B1,B2,B3<:CompositeBasis}
-    N = length(state.basis_l.shape)
+function expect(indices, op::AbstractOperator{OperatorBasis{B1,B2}}, state::AbstractOperator{OperatorBasis{B3,B3}}) where {B1,B2,B3<:CompositeBasis}
+    N = length(fullbasis(state).left.shape)
     indices_ = complement(N, indices)
     expect(op, ptrace(state, indices_))
 end
 
-expect(index::Integer, op::AbstractOperator{B1,B2}, state::AbstractOperator{B3,B3}) where {B1,B2,B3<:CompositeBasis} = expect([index], op, state)
+expect(index::Integer, op::AbstractOperator{OperatorBasis{B1,B2}}, state::AbstractOperator{OperatorBasis{B3,B3}}) where {B1,B2,B3<:CompositeBasis} = expect([index], op, state)
 expect(op::AbstractOperator, states::Vector) = [expect(op, state) for state=states]
 expect(indices, op::AbstractOperator, states::Vector) = [expect(indices, op, state) for state=states]
+expect(op::AbstractOperator{B,B}, state::AbstractKet{B}) where B = norm(op * state)^2
 
-expect(op::AbstractOperator{B1,B2}, state::AbstractOperator{B2,B2}) where {B1,B2} = tr(op*state)
+expect(op::AbstractOperator{OperatorBasis{B1,B2}}, state::AbstractOperator{OperatorBasis{B2,B2}}) where {B1,B2} = tr(op*state)
 
 """
     variance(index, op, state)
 
 If an `index` is given, it assumes that `op` is defined in the subsystem specified by this number
 """
-function variance(indices, op::AbstractOperator{B,B}, state::AbstractOperator{BC,BC}) where {B,BC<:CompositeBasis}
-    N = length(state.basis_l.shape)
+function variance(indices, op::AbstractOperator{OperatorBasis{B,B}}, state::AbstractOperator{OperatorBasis{BC,BC}}) where {B,BC<:CompositeBasis}
+    N = length(fullbasis(state).left.shape)
     indices_ = complement(N, indices)
     variance(op, ptrace(state, indices_))
 end
 
-variance(index::Integer, op::AbstractOperator{B,B}, state::AbstractOperator{BC,BC}) where {B,BC<:CompositeBasis} = variance([index], op, state)
+variance(index::Integer, op::AbstractOperator{OperatorBasis{B,B}}, state::AbstractOperator{OperatorBasis{BC,BC}}) where {B,BC<:CompositeBasis} = variance([index], op, state)
 variance(op::AbstractOperator, states::Vector) = [variance(op, state) for state=states]
 variance(indices, op::AbstractOperator, states::Vector) = [variance(indices, op, state) for state=states]
 
-function variance(op::AbstractOperator{B,B}, state::AbstractOperator{B,B}) where B
+function variance(op::AbstractOperator{OperatorBasis{B,B}}, state::AbstractOperator{OperatorBasis{B,B}}) where B
     expect(op*op, state) - expect(op, state)^2
 end

src/identityoperator.jl

@@ -11,15 +11,17 @@ type which has to a subtype of [`AbstractOperator`](@ref) as well as the number
 to be used in the identity matrix.
 """
 identityoperator(::Type{T}, ::Type{S}, b1::Basis, b2::Basis) where {T<:AbstractOperator,S} = throw(ArgumentError("Identity operator not defined for operator type $T."))
+identityoperator(::Type{T}, ::Type{S}, b::OperatorBasis) where {T<:AbstractOperator,S} = identityoperator(T,S,b.left,b.right)
 identityoperator(::Type{T}, ::Type{S}, b::Basis) where {T<:AbstractOperator,S} = identityoperator(T,S,b,b)
-identityoperator(::Type{T}, bases::Basis...) where T<:AbstractOperator = identityoperator(T,eltype(T),bases...)
+identityoperator(::Type{T}, b::OperatorBasis) where {T<:AbstractOperator} = identityoperator(T,eltype(T),b)
+identityoperator(::Type{T}, bases::Basis...) where {T<:AbstractOperator} = identityoperator(T,eltype(T),bases...)
 identityoperator(b::Basis) = identityoperator(ComplexF64,b)
-identityoperator(op::T) where {T<:AbstractOperator} = identityoperator(T, op.basis_l, op.basis_r)
+identityoperator(op::T) where {T<:AbstractOperator} = identityoperator(T, fullbasis(op))
 
 # Catch case where eltype cannot be inferred from type; this is a bit hacky
 identityoperator(::Type{T}, ::Type{Any}, b1::Basis, b2::Basis) where T<:AbstractOperator = identityoperator(T, ComplexF64, b1, b2)
 
 identityoperator(b1::Basis, b2::Basis) = identityoperator(ComplexF64, b1, b2)
 
 """Prepare the identity superoperator over a given space."""
-function identitysuperoperator end
+function identitysuperoperator end

src/julia_base.jl

@@ -8,19 +8,19 @@ addnumbererror() = throw(ArgumentError("Can't add or subtract a number and an op
 # States
 ##
 
--(a::T) where {T<:StateVector} = T(a.basis, -a.data)
+-(a::T) where {T<:StateVector} = T(a.basis, -a.data) # FIXME
 *(a::StateVector, b::Number) = b*a
-copy(a::T) where {T<:StateVector} = T(a.basis, copy(a.data))
-length(a::StateVector) = length(a.basis)::Int
-basis(a::StateVector) = a.basis
+copy(a::T) where {T<:StateVector} = T(a.basis, copy(a.data)) # FIXME
+length(a::StateVector) = length(basis(a))::Int
+basis(a::StateVector) = fullbasis(a)
 directsum(x::StateVector...) = reduce(directsum, x)
 
 # Array-like functions
-Base.size(x::StateVector) = size(x.data)
-@inline Base.axes(x::StateVector) = axes(x.data)
+Base.size(x::StateVector) = size(x.data) # FIXME
+@inline Base.axes(x::StateVector) = axes(x.data) #FIXME
 Base.ndims(x::StateVector) = 1
 Base.ndims(::Type{<:StateVector}) = 1
-Base.eltype(x::StateVector) = eltype(x.data)
+Base.eltype(x::StateVector) = eltype(x.data) # FIXME
 
 # Broadcasting
 Base.broadcastable(x::StateVector) = x
@@ -32,9 +32,9 @@ Base.adjoint(a::StateVector) = dagger(a)
 # Operators
 ##
 
-length(a::AbstractOperator) = length(a.basis_l)::Int*length(a.basis_r)::Int
-basis(a::AbstractOperator) = (check_samebases(a); a.basis_l)
-basis(a::AbstractSuperOperator) = (check_samebases(a); a.basis_l[1])
+length(a::AbstractOperator) = (b=fullbasis(a); length(b.left)::Int*length(b.right)::Int)
+basis(a::AbstractOperator) = (b=fullbasis(a); check_samebases(b); b.left)
+basis(a::AbstractSuperOperator) = (b=fullbasis(a); check_samebases(b); b.left.left)
 
 # Ensure scalar broadcasting
 Base.broadcastable(x::AbstractOperator) = Ref(x)
@@ -60,11 +60,11 @@ Operator exponential.
 """
 exp(op::AbstractOperator) = throw(ArgumentError("exp() is not defined for this type of operator: $(typeof(op)).\nTry to convert to dense operator first with dense()."))
 
-Base.size(op::AbstractOperator) = (length(op.basis_l),length(op.basis_r))
+Base.size(op::AbstractOperator) = (b=fullbasis(op); (length(b.left),length(b.right)))
 function Base.size(op::AbstractOperator, i::Int)
     i < 1 && throw(ErrorException("dimension index is < 1"))
     i > 2 && return 1
-    i==1 ? length(op.basis_l) : length(op.basis_r)
+    i==1 ? length(fullbasis(op).left) : length(fullbasis(op).right)
 end
 
 Base.adjoint(a::AbstractOperator) = dagger(a)

src/julia_linalg.jl

@@ -17,7 +17,7 @@ tr(x::AbstractOperator) = arithmetic_unary_error("Trace", x)
 
 Norm of the given bra or ket state.
 """
-norm(x::StateVector) = norm(x.data)
+norm(x::StateVector) = norm(x.data) # FIXME
 
 """
     normalize(x::StateVector)
@@ -31,7 +31,7 @@ normalize(x::StateVector) = x/norm(x)
 
 In-place normalization of the given bra or ket so that `norm(x)` is one.
 """
-normalize!(x::StateVector) = (normalize!(x.data); x)
+normalize!(x::StateVector) = (normalize!(x.data); x) # FIXME
 
 """
     normalize(op)

src/linalg.jl

@@ -1,7 +1,13 @@
-samebases(a::AbstractOperator) = samebases(a.basis_l, a.basis_r)::Bool
-samebases(a::AbstractOperator, b::AbstractOperator) = samebases(a.basis_l, b.basis_l)::Bool && samebases(a.basis_r, b.basis_r)::Bool
-check_samebases(a::Union{AbstractOperator, AbstractSuperOperator}) = check_samebases(a.basis_l, a.basis_r)
-multiplicable(a::AbstractOperator, b::AbstractOperator) = multiplicable(a.basis_r, b.basis_l)
+samebases(a::AbstractOperator) = samebases(fullbasis(a))::Bool
+samebases(a::AbstractSuperOperator) = samebases(fullbasis(a))::Bool
+samebases(a::AbstractOperator, b::AbstractOperator) = samebases(fullbasis(a), fullbasis(b))::Bool
+samebases(a::AbstractSuperOperator, b::AbstractSuperOperator) = samebases(fullbasis(a), fullbasis(b))::Bool
+check_samebases(a::AbstractOperator) = check_samebases(fullbasis(a))::Bool
+check_samebases(a::AbstractSuperOperator) = check_samebases(fullbasis(a))::Bool
+check_samebases(a::AbstractOperator, b::AbstractOperator) = check_samebases(fullbasis(a), fullbasis(b))::Bool
+check_samebases(a::AbstractSuperOperator, b::AbstractSuperOperator) = check_samebases(fullbasis(a), fullbasis(b))::Bool
+
+multiplicable(a::AbstractOperator, b::AbstractOperator) = multiplicable(fullbasis(a).right, fullbasis(b).left)
 dagger(a::AbstractOperator) = arithmetic_unary_error("Hermitian conjugate", a)
 transpose(a::AbstractOperator) = arithmetic_unary_error("Transpose", a)
 directsum(a::AbstractOperator...) = reduce(directsum, a)