Fix origin of run_multiple issue by returning copies of sv/dm as ap…

…propriate (#33)

src/BraketSimulator.jl

@@ -352,8 +352,7 @@ end
         n_task_threads = min(max_parallel_threads, n_tasks)
 
         results = Vector{Braket.GateModelTaskResult}(undef, n_tasks)
-        function process_work()
-            my_sim = copy(simulator)
+        function process_work(my_sim)
             while isready(todo_tasks_ch)
                 my_ix = -1
                 # need to lock the channel as it may become empty
@@ -374,7 +373,7 @@ end
         tasks = Vector{Task}(undef, n_task_threads)
         # need sync here to ensure all the spawns launch
         @sync for worker in 1:n_task_threads
-            tasks[worker] = Threads.@spawn process_work()
+            tasks[worker] = Threads.@spawn process_work(similar(simulator))
         end
         # tasks don't return anything so we can wait rather than fetch
         wait.(tasks)

src/dm_simulator.jl

@@ -252,7 +252,7 @@ function expectation(
     return real(sum(diag(dm_copy)))
 end
 state_vector(dms::DensityMatrixSimulator)   = diag(dms.density_matrix)
-density_matrix(dms::DensityMatrixSimulator) = dms.density_matrix
+density_matrix(dms::DensityMatrixSimulator) = copy(dms.density_matrix)
 probabilities(dms::DensityMatrixSimulator)  = real.(diag(dms.density_matrix))
 
 function swap_bits(ix::Int, qubit_map::Dict{Int,Int})

src/sv_simulator.jl

@@ -149,7 +149,7 @@ function evolve!(
     return svs
 end
 
-state_vector(svs::StateVectorSimulator) = svs.state_vector
+state_vector(svs::StateVectorSimulator) = copy(svs.state_vector)
 density_matrix(svs::StateVectorSimulator) =
     kron(svs.state_vector, adjoint(svs.state_vector))