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Merged
merged 5 commits into from
Aug 29, 2025
Merged

Add QobjEvo support for SteadyStateODESolver #536

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a61bfa2
Add steaystate ode kwargs passing
Aug 28, 2025
1471726
add support of `QobjEvo` for `SteadyStateODESolver`
Aug 28, 2025
7b66757
fix typo
Aug 28, 2025
34f74c3
fix methods
Aug 28, 2025
ed7e22b
remove autodiff tests for steadystate
Aug 28, 2025
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3 changes: 3 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)

- Add support of `QobjEvo` for `steadystate` (ODE solver only). ([#536])

## [v0.34.1]
Release date: 2025-08-23

Expand Down Expand Up @@ -301,3 +303,4 @@ Release date: 2024-11-13
[#517]: https://github.com/qutip/QuantumToolbox.jl/issues/517
[#520]: https://github.com/qutip/QuantumToolbox.jl/issues/520
[#531]: https://github.com/qutip/QuantumToolbox.jl/issues/531
[#536]: https://github.com/qutip/QuantumToolbox.jl/issues/536
10 changes: 7 additions & 3 deletions src/steadystate.jl
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Expand Up @@ -96,7 +96,7 @@ end

@doc raw"""
steadystate(
H::QuantumObject{OpType},
H::AbstractQuantumObject{OpType},
c_ops::Union{Nothing,AbstractVector,Tuple} = nothing;
solver::SteadyStateSolver = SteadyStateDirectSolver(),
kwargs...,
Expand All @@ -111,7 +111,7 @@ Solve the stationary state based on different solvers.
- `kwargs`: The keyword arguments for the solver.
"""
function steadystate(
H::QuantumObject{OpType},
H::AbstractQuantumObject{OpType},
c_ops::Union{Nothing,AbstractVector,Tuple} = nothing;
solver::SteadyStateSolver = SteadyStateDirectSolver(),
kwargs...,
Expand Down Expand Up @@ -199,7 +199,7 @@ function _steadystate(L::QuantumObject{SuperOperator}, solver::SteadyStateDirect
return QuantumObject(ρss, Operator(), L.dimensions)
end

function _steadystate(L::QuantumObject{SuperOperator}, solver::SteadyStateODESolver; kwargs...)
function _steadystate(L::AbstractQuantumObject{SuperOperator}, solver::SteadyStateODESolver; kwargs...)
tmax = solver.tmax

ψ0 = isnothing(solver.ψ0) ? rand_ket(L.dimensions) : solver.ψ0
Expand All @@ -217,12 +217,16 @@ function _steadystate(L::QuantumObject{SuperOperator}, solver::SteadyStateODESol
save_everystep = false,
saveat = ftype[],
callback = cb,
kwargs...,
)

ρss = sol.states[end]
return ρss
end

_steadystate(L::QuantumObjectEvolution{SuperOperator}, solver::SteadyStateSolver; kwargs...) =
throw(ArgumentError("$(get_typename_wrapper(solver)) does not support QobjEvo."))

struct SteadyStateODECondition{CT<:AbstractArray}
cache::CT
end
Expand Down
8 changes: 4 additions & 4 deletions test/core-test/steady_state.jl
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Expand Up @@ -3,6 +3,7 @@
a = destroy(N)
a_d = a'
H = a_d * a + 0.1 * (a + a_d)
Ht = QobjEvo(H, (p, t) -> 1) # for test throw
c_ops = [sqrt(0.1) * a]
e_ops = [a_d * a]
psi0 = fock(N, 3)
Expand All @@ -17,18 +18,17 @@
solver = SteadyStateDirectSolver()
ρ_ss = steadystate(H, c_ops, solver = solver)
@test tracedist(rho_me, ρ_ss) < 1e-4
@test_throws ArgumentError steadystate(Ht, c_ops, solver = solver)

solver = SteadyStateLinearSolver()
ρ_ss = steadystate(H, c_ops, solver = solver)
@test tracedist(rho_me, ρ_ss) < 1e-4

solver = SteadyStateLinearSolver()
ρ_ss = steadystate(H, c_ops, solver = solver)
@test tracedist(rho_me, ρ_ss) < 1e-4
Comment on lines -25 to -27
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@ytdHuang ytdHuang Aug 28, 2025

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we remove this part because there is exact same thing in Lines 21 - 23

@test_throws ArgumentError steadystate(Ht, c_ops, solver = solver)

solver = SteadyStateEigenSolver()
ρ_ss = steadystate(H, c_ops, solver = solver)
@test tracedist(rho_me, ρ_ss) < 1e-4
@test_throws ArgumentError steadystate(Ht, c_ops, solver = solver)

@testset "Type Inference (steadystate)" begin
L = liouvillian(H, c_ops)
Expand Down
15 changes: 15 additions & 0 deletions test/ext-test/cpu/autodiff/autodiff.jl
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Expand Up @@ -67,6 +67,17 @@ function my_f_mesolve(p)
return real(expect(a' * a, sol.states[end]))
end

function my_f_steadystate(p)
ρss = steadystate(
L,
SteadyStateODESolver(ψ0 = ψ0_mesolve, tmax = tlist_mesolve[end]);
params = p,
sensealg = BacksolveAdjoint(autojacvec = EnzymeVJP()),
)

return real(expect(a' * a, ρss))
end

# Analytical solution
n_ss(Δ, F, γ) = abs2(F / (Δ + 1im * γ / 2))

Expand Down Expand Up @@ -113,8 +124,12 @@ n_ss(Δ, F, γ) = abs2(F / (Δ + 1im * γ / 2))

my_f_mesolve_direct(params)
my_f_mesolve(params)
my_f_steadystate(params)

# calculate exact solution and check if steadystate works
grad_exact = Zygote.gradient((p) -> n_ss(p[1], p[2], p[3]), params)[1]
grad_ss = Zygote.gradient(my_f_steadystate, params)[1]
@test grad_ss ≈ grad_exact atol=1e-6

@testset "ForwardDiff.jl" begin
grad_qt = ForwardDiff.gradient(my_f_mesolve_direct, params)
Expand Down
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