Introduce Gabs extensions for Gaussian state and unitary conversions (#124)

* add Gabs as an extension

* introduce `GabsRepr` from QInterface 0.4.0

* add v0.4.1 for QInterface for tensor conversions

* add supporting Gabs tests

* rm emptyline

* bump Gabs to v1.3.1 for QInterface compat

* update changelog and bump to v0.4.12-dev

Author: apkille

CHANGELOG.md

@@ -1,5 +1,9 @@
 # News
 
+## v0.4.12 - dev
+
+- Add Gabs extension for numerical translations of symbolic Gaussian states and operators.
+
 ## v0.4.11 - 2025-06-22
 
 - Bump compats for QuantumInterface and QuantumClifford.

Project.toml

@@ -1,7 +1,7 @@
 name = "QuantumSymbolics"
 uuid = "efa7fd63-0460-4890-beb7-be1bbdfbaeae"
 authors = ["QuantumSymbolics.jl contributors"]
-version = "0.4.11"
+version = "0.4.12-dev"
 
 [deps]
 Latexify = "23fbe1c1-3f47-55db-b15f-69d7ec21a316"
@@ -14,21 +14,24 @@ Symbolics = "0c5d862f-8b57-4792-8d23-62f2024744c7"
 TermInterface = "8ea1fca8-c5ef-4a55-8b96-4e9afe9c9a3c"
 
 [weakdeps]
+Gabs = "0eb812ee-a11f-4f5e-b8d4-bb8a44f06f50"
 QuantumClifford = "0525e862-1e90-11e9-3e4d-1b39d7109de1"
 QuantumOpticsBase = "4f57444f-1401-5e15-980d-4471b28d5678"
 
 [extensions]
+GabsExt = "Gabs"
 MixedCliffordOpticsExt = ["QuantumClifford", "QuantumOpticsBase"]
 QuantumCliffordExt = "QuantumClifford"
 QuantumOpticsExt = "QuantumOpticsBase"
 
 [compat]
+Gabs = "1.3.1"
 Latexify = "0.16"
 LinearAlgebra = "1.9"
 MacroTools = "0.5.13"
 PrecompileTools = "1.2"
 QuantumClifford = "0.8.19, 0.9, 0.10"
-QuantumInterface = "0.3.7, 0.4"
+QuantumInterface = "0.3.7, 0.4.1"
 QuantumOpticsBase = "0.4.22, 0.5"
 SymbolicUtils = "3.7"
 Symbolics = "6"

ext/GabsExt/GabsExt.jl

@@ -0,0 +1,32 @@
+module GabsExt
+
+using QuantumSymbolics
+using QuantumSymbolics: CoherentState, GabsRepr
+import QuantumSymbolics: express, express_nolookup
+
+using Gabs
+
+function express_nolookup(x::FockState, repr::GabsRepr)
+    x.idx == 0 || throw(ArgumentError("Fock states with index ≥ 0 are non-Gaussian and unsupported via the Gabs representation."))
+    return vacuumstate(repr.basis(1))
+end
+express_nolookup(x::CoherentState, repr::GabsRepr) = coherentstate(repr.basis(1), x.alpha)
+express_nolookup(x::BosonicThermalState, repr::GabsRepr) = thermalstate(repr.basis(1), x.photons)
+express_nolookup(x::PhaseShiftOp, repr::GabsRepr) = phaseshift(repr.basis(1), x.phase)
+express_nolookup(x::DisplaceOp, repr::GabsRepr) = displace(repr.basis(1), x.alpha)
+express_nolookup(x::BeamSplitterOp, repr::GabsRepr) = beamsplitter(repr.basis(2), x.transmit)
+
+for (f,g) in [(:SqueezedState, :squeezedstate),(:SqueezeOp,:squeeze)]
+    @eval function express_nolookup(x::$f, repr::GabsRepr)
+        r, i = (real(x.z), imag(x.z))
+        return ($g)(repr.basis(1), sqrt(r^2 + i^2), atan(i, r))
+    end
+end
+for (f,g) in [(:TwoSqueezedState, :eprstate),(:TwoSqueezeOp,:twosqueeze)]
+    @eval function express_nolookup(x::$f, repr::GabsRepr)
+        r, i = (real(x.z), imag(x.z))
+        return ($g)(repr.basis(2), sqrt(r^2 + i^2), atan(i, r))
+    end
+end
+
+end

src/QSymbolicsBase/QSymbolicsBase.jl

@@ -18,11 +18,11 @@ import QuantumInterface:
     projector,dagger,tr,ptrace,
     AbstractBra,AbstractKet,AbstractOperator,AbstractSuperOperator,
     express,AbstractRepresentation,AbstractUse,UseAsState,UseAsObservable,UseAsOperation,
-    QuantumOpticsRepr,QuantumMCRepr,CliffordRepr
+    QuantumOpticsRepr,QuantumMCRepr,CliffordRepr,GabsRepr
 
 export SymQObj,QObj,
        AbstractRepresentation,AbstractUse,
-       QuantumOpticsRepr,QuantumMCRepr,CliffordRepr,
+       QuantumOpticsRepr,QuantumMCRepr,CliffordRepr,GabsRepr,
        UseAsState,UseAsObservable,UseAsOperation,
        apply!,
        express,

test/Project.toml

@@ -1,6 +1,7 @@
 [deps]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
+Gabs = "0eb812ee-a11f-4f5e-b8d4-bb8a44f06f50"
 Graphs = "86223c79-3864-5bf0-83f7-82e725a168b6"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"

test/test_gabs.jl

@@ -0,0 +1,33 @@
+@testitem "Gabs objects" begin
+    using QuantumSymbolics
+    using Gabs
+
+    α = rand(ComplexF64)
+    r, θ, τ = rand(Float64), rand(Float64), rand(Float64)
+    n̄ = rand(1:10)
+
+    for basis in [QuadBlockBasis, QuadPairBasis]
+        @testset "Gaussian states - $(basis)" begin
+            @test express(vac, GabsRepr(basis)) ≈ vacuumstate(basis(1))
+            @test express(CoherentState(α), GabsRepr(basis)) ≈ coherentstate(basis(1), α)
+            @test express(SqueezedState(r*exp(im*θ)), GabsRepr(basis)) ≈ squeezedstate(basis(1), r, θ)
+            @test express(TwoSqueezedState(r*exp(im*θ)), GabsRepr(basis)) ≈ eprstate(basis(2), r, θ)
+            @test express(BosonicThermalState(n̄), GabsRepr(basis)) ≈ thermalstate(basis(1), n̄)
+        end
+
+        @testset "Gaussian unitaries - $(basis)" begin
+            @test express(PhaseShiftOp(θ), GabsRepr(basis)) ≈ phaseshift(basis(1), θ)
+            @test express(DisplaceOp(α), GabsRepr(basis)) ≈ displace(basis(1), α)
+            @test express(SqueezeOp(r*exp(im*θ)), GabsRepr(basis)) ≈ squeeze(basis(1), r, θ)
+            @test express(TwoSqueezeOp(r*exp(im*θ)), GabsRepr(basis)) ≈ twosqueeze(basis(2), r, θ)
+            @test express(BeamSplitterOp(τ), GabsRepr(basis)) ≈ beamsplitter(basis(2), τ)
+        end
+
+        @testset "Linear algebra operations" begin
+            @test express(CoherentState(α) ⊗ TwoSqueezedState(r*exp(im*θ)) ⊗ vac, GabsRepr(basis)) ≈ coherentstate(basis(1), α) ⊗ eprstate(basis(2), r, θ) ⊗ vacuumstate(basis(1))
+            @test express(DisplaceOp(α) * vac, GabsRepr(basis)) ≈ coherentstate(basis(1), α)
+            @test express(DisplaceOp(α) ⊗ SqueezeOp(r*exp(im*θ)) * (vac ⊗ vac), GabsRepr(basis)) ≈ coherentstate(basis(1), α) ⊗ squeezedstate(basis(1), r, θ)
+            @test_broken express(ptrace(DisplaceOp(α) ⊗ PhaseShiftOp(θ) ⊗ BeamSplitterOp(τ), [2, 3]), GabsRepr(basis)) ≈ ptrace(displace(basis(1), α) ⊗ phaseshift(basis(1), θ) ⊗ beamsplitter(basis(2), τ), [2, 3])
+        end
+    end
+end