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Add missing Gaussian QuantumOpticsExt conversions (#181)
Co-authored-by: Stefan Krastanov <stefan@krastanov.org> Co-authored-by: Stefan Krastanov <github.acc@krastanov.org>
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‎CHANGELOG.md‎

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# News
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## v0.4.15 - 2026-03-19
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- `QuantumOpticsRepr` support for BosonicThermalState, PhaseShiftOp, BeamSplitterOp, TwoSqueezedState, TwoSqueezeOp
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## v0.4.14 - 2026-03-03
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- Improvements and regression tests for `tensor` of operators when expressed in `CliffordRepr` (depending on the newly added private `QCGateSequence` in `QuantumCliffordExt`).

‎Project.toml‎

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name = "QuantumSymbolics"
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uuid = "efa7fd63-0460-4890-beb7-be1bbdfbaeae"
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authors = ["QuantumSymbolics.jl contributors"]
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version = "0.4.14"
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version = "0.4.15"
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[workspace]
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projects = ["benchmark", "docs"]

‎ext/QuantumOpticsExt/QuantumOpticsExt.jl‎

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@@ -93,6 +93,8 @@ express_nolookup(o::SqueezeOp, r::QuantumOpticsRepr) = squeeze(finite_basis(o,r)
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express_nolookup(x::MixedState, r::QuantumOpticsRepr) = identityoperator(finite_basis(x,r))/length(finite_basis(x,r)) # TODO there is probably a more efficient way to represent it
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express_nolookup(x::IdentityOp, r::QuantumOpticsRepr) = identityoperator(finite_basis(x,r))
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include("gaussian.jl")
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express_nolookup(p::PauliNoiseCPTP, ::QuantumOpticsRepr) = LazySuperSum(SpinBasis(1//2), [1-p.px-p.py-p.pz,p.px,p.py,p.pz],
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[LazyPrePost(_id,_id),LazyPrePost(_x,_x),LazyPrePost(_y,_y),LazyPrePost(_z,_z)])
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‎ext/QuantumOpticsExt/gaussian.jl‎

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using LinearAlgebra: diagm
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finite_two_mode_basis(s, r) = isfinite(length(basis(s))) ? basis(s) : FockBasis(r.cutoff)^2
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function _thermalstate(basis, photons)
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occupation = photons / (photons + 1)
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weights = occupation .^ collect(basis.offset:basis.N)
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normalize(DenseOperator(basis, diagm(0 => weights)))
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end
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function _two_mode_ops(basis)
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mode_basis = basis.bases[1]
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return (
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a1 = embed(basis, 1, destroy(mode_basis)),
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a2 = embed(basis, 2, destroy(mode_basis)),
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ad1 = embed(basis, 1, create(mode_basis)),
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ad2 = embed(basis, 2, create(mode_basis)),
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)
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end
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_phaseshift(basis, phase) = exp(-im * phase * dense(number(basis)))
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function _beamsplitter(basis, transmit)
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ops = _two_mode_ops(basis)
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theta = asin(sqrt(transmit))
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exp(theta * dense(ops.ad1 * ops.a2 - ops.a1 * ops.ad2))
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end
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function _twosqueeze(basis, z)
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ops = _two_mode_ops(basis)
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exp(dense(conj(z) * ops.a1 * ops.a2 - z * ops.ad1 * ops.ad2))
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end
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function _two_mode_vacuum(basis)
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vacuum = fockstate(basis.bases[1], 0)
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vacuum ⊗ vacuum
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end
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express_nolookup(s::BosonicThermalState, r::QuantumOpticsRepr) = _thermalstate(finite_basis(s,r), s.photons)
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express_nolookup(o::PhaseShiftOp, r::QuantumOpticsRepr) = _phaseshift(finite_basis(o,r), o.phase)
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express_nolookup(o::BeamSplitterOp, r::QuantumOpticsRepr) = _beamsplitter(finite_two_mode_basis(o,r), o.transmit)
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express_nolookup(s::TwoSqueezedState, r::QuantumOpticsRepr) = (b = finite_two_mode_basis(s,r); _twosqueeze(b, s.z) * _two_mode_vacuum(b))
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express_nolookup(o::TwoSqueezeOp, r::QuantumOpticsRepr) = _twosqueeze(finite_two_mode_basis(o,r), o.z)

‎test/test_gabs_qo_interop.jl‎

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@testitem "Gabs and QuantumOptics Gaussian interop" begin
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using Gabs
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using QuantumOptics
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using QuantumSymbolics
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samestate(ket1, ket2; atol=1e-10) = isapprox(dm(ket1), dm(ket2); atol=atol, rtol=0)
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express_via_gabs(state, repr, basis) = express(express(state, GabsRepr(basis)), repr)
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function act_via_gabs(op, state, repr, basis)
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grepr = GabsRepr(basis)
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express(express(op, grepr) * express(state, grepr), repr)
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end
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direct_action(op, state, repr) = express(op, repr) * express(state, repr)
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symbolic_action(op, state, repr) = express(op * state, repr)
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@testset "Pure-state conversions" begin
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repr = QuantumOpticsRepr(14)
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α = 0.21 - 0.13im
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z = 0.17 * exp(-0.3im)
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direct_vacuum = express(vac, repr)
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direct_product = express(CoherentState(α) ⊗ vac, repr)
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direct_twomode_squeezed = express(TwoSqueezedState(z), repr)
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for basis in (QuadPairBasis, QuadBlockBasis)
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@test samestate(express_via_gabs(vac, repr, basis), direct_vacuum)
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@test samestate(express_via_gabs(CoherentState(α) ⊗ vac, repr, basis), direct_product)
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@test samestate(
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express_via_gabs(TwoSqueezedState(z), repr, basis),
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direct_twomode_squeezed;
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atol=1e-9,
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)
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end
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pair_state = express_via_gabs(TwoSqueezedState(z), repr, QuadPairBasis)
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block_state = express_via_gabs(TwoSqueezedState(z), repr, QuadBlockBasis)
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@test samestate(pair_state, block_state; atol=1e-9)
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end
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@testset "Simple edge cases" begin
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repr = QuantumOpticsRepr(14)
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α = 0.21 - 0.13im
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z = 0.0 + 0.2im
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πf = float(pi)
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for basis in (QuadPairBasis, QuadBlockBasis)
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@test samestate(
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act_via_gabs(PhaseShiftOp(0.0), CoherentState(α), repr, basis),
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express(CoherentState(α), repr),
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)
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@test samestate(
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act_via_gabs(PhaseShiftOp(πf), CoherentState(α), repr, basis),
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express(CoherentState(-α), repr),
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)
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@test samestate(
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act_via_gabs(BeamSplitterOp(0.0), CoherentState(α) ⊗ vac, repr, basis),
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express(CoherentState(α) ⊗ vac, repr),
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)
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@test samestate(
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act_via_gabs(BeamSplitterOp(1.0), CoherentState(α) ⊗ vac, repr, basis),
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express(vac ⊗ CoherentState(-α), repr),
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)
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@test samestate(
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act_via_gabs(TwoSqueezeOp(0.0 + 0.0im), vac ⊗ vac, repr, basis),
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express(vac ⊗ vac, repr),
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)
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@test samestate(
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act_via_gabs(TwoSqueezeOp(z), vac ⊗ vac, repr, basis),
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express(TwoSqueezedState(z), repr),
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)
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end
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end
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@testset "Operator actions agree across paths" begin
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repr = QuantumOpticsRepr(14)
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α = 0.21 - 0.13im
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z = 0.17 * exp(-0.3im)
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phase = PhaseShiftOp(pi / 2)
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beamsplitter = BeamSplitterOp(0.35)
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twosqueeze = TwoSqueezeOp(z)
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phase_state = CoherentState(α)
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twomode_state = CoherentState(α) ⊗ vac
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vacuum_pair = vac ⊗ vac
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phase_direct = direct_action(phase, phase_state, repr)
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phase_symbolic = symbolic_action(phase, phase_state, repr)
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@test samestate(phase_symbolic, phase_direct)
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beamsplitter_direct = direct_action(beamsplitter, twomode_state, repr)
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beamsplitter_symbolic = symbolic_action(beamsplitter, twomode_state, repr)
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@test samestate(beamsplitter_symbolic, beamsplitter_direct)
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twosqueeze_direct = direct_action(twosqueeze, twomode_state, repr)
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twosqueeze_symbolic = symbolic_action(twosqueeze, twomode_state, repr)
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@test samestate(twosqueeze_symbolic, twosqueeze_direct; atol=1e-9)
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twosqueeze_vacuum_direct = direct_action(twosqueeze, vacuum_pair, repr)
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twosqueeze_vacuum_symbolic = symbolic_action(twosqueeze, vacuum_pair, repr)
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twosqueeze_state = express(TwoSqueezedState(z), repr)
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@test samestate(twosqueeze_vacuum_symbolic, twosqueeze_vacuum_direct)
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@test samestate(twosqueeze_vacuum_symbolic, twosqueeze_state)
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for basis in (QuadPairBasis, QuadBlockBasis)
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phase_via_gabs = act_via_gabs(phase, phase_state, repr, basis)
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@test samestate(phase_via_gabs, phase_direct)
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beamsplitter_via_gabs = act_via_gabs(beamsplitter, twomode_state, repr, basis)
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@test samestate(beamsplitter_via_gabs, beamsplitter_direct)
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twosqueeze_via_gabs = act_via_gabs(twosqueeze, twomode_state, repr, basis)
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@test samestate(twosqueeze_via_gabs, twosqueeze_direct; atol=1e-9)
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twosqueeze_vacuum_via_gabs = act_via_gabs(twosqueeze, vacuum_pair, repr, basis)
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@test samestate(twosqueeze_vacuum_via_gabs, twosqueeze_state; atol=1e-9)
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end
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pair_state = act_via_gabs(twosqueeze, twomode_state, repr, QuadPairBasis)
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block_state = act_via_gabs(twosqueeze, twomode_state, repr, QuadBlockBasis)
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@test samestate(pair_state, block_state; atol=1e-9)
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end
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end

‎test/test_qo_gaussian.jl‎

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@testitem "Test qo gaussian" begin
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using LinearAlgebra: diagm
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using QuantumOptics
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using QuantumSymbolics
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samestate(ket1, ket2; atol=1e-10) = isapprox(dm(ket1), dm(ket2); atol=atol, rtol=0)
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function two_mode_ops(cutoff)
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mode_basis = FockBasis(cutoff)
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basis = mode_basis^2
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return (
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basis = basis,
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vacuum = fockstate(mode_basis, 0) ⊗ fockstate(mode_basis, 0),
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a1 = embed(basis, 1, destroy(mode_basis)),
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a2 = embed(basis, 2, destroy(mode_basis)),
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ad1 = embed(basis, 1, create(mode_basis)),
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ad2 = embed(basis, 2, create(mode_basis)),
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)
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end
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@testset "Single-mode Gaussian objects" begin
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repr = QuantumOpticsRepr(10)
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basis = FockBasis(repr.cutoff)
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α = 0.2 - 0.1im
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θ = 0.3
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n̄ = 1.2
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thermal = express(BosonicThermalState(n̄), repr)
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weights = (n̄ / (n̄ + 1)) .^ collect(basis.offset:basis.N)
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expected_thermal = normalize(DenseOperator(basis, diagm(0 => weights)))
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@test thermal ≈ expected_thermal
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@test express(PhaseShiftOp(θ), repr) ≈ exp(-im * θ * dense(number(basis)))
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@test samestate(
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express(PhaseShiftOp(θ) * CoherentState(α), repr),
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coherentstate(basis, α * exp(-im * θ)),
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)
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@test express(PhaseShiftOp(θ) * BosonicThermalState(n̄) * dagger(PhaseShiftOp(θ)), repr) ≈ thermal
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end
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@testset "Two-mode Gaussian objects" begin
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repr = QuantumOpticsRepr(8)
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ops = two_mode_ops(repr.cutoff)
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z = 0.17 * exp(-0.3im)
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τ = 0.35
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twosqueeze = exp(dense(conj(z) * ops.a1 * ops.a2 - z * ops.ad1 * ops.ad2))
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beamsplitter = exp(asin(sqrt(τ)) * dense(ops.ad1 * ops.a2 - ops.a1 * ops.ad2))
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@test express(TwoSqueezeOp(z), repr) ≈ twosqueeze
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@test samestate(express(TwoSqueezedState(z), repr), twosqueeze * ops.vacuum)
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@test samestate(express(TwoSqueezeOp(z) * (vac ⊗ vac), repr), express(TwoSqueezedState(z), repr))
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@test express(BeamSplitterOp(τ), repr) ≈ beamsplitter
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@test samestate(
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express(BeamSplitterOp(τ) * (CoherentState(0.1 + 0.2im) ⊗ vac), repr),
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beamsplitter * express(CoherentState(0.1 + 0.2im) ⊗ vac, repr),
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)
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end
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end

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