transverse field ising

src/SimpleTDVP.jl

@@ -10,7 +10,7 @@ export MPS, nsite, nflavor, vec2mps, IndexStore, newindex!, code_mps2vec, rand_m
 export product_mps, ghz_mps
 export left_move!, right_move!, canonical_move!, is_canonicalized, canonical_center, to_left_canonical!, to_right_canonical!
 export mat, MPO, code_mpo2mat, mat2mpo, rand_mpo
-export heisenberg_mpo
+export heisenberg_mpo, transverse_ising_mpo
 export dot, sandwich, compress!, num_of_elements
 export dmrg!, dmrg
 export TensorLayout

src/mpo.jl

@@ -121,4 +121,15 @@ function heisenberg_mpo(::Type{T}, n::Int) where T
     tensor1[1, :, :, 3] = tensor2[3, :, :, 5] = tensor2[1, :, :, 3] = tensor3[3, :, :, 1] = Matrix{T}(Y)
     tensor1[1, :, :, 4] = tensor2[4, :, :, 5] = tensor2[1, :, :, 4] = tensor3[4, :, :, 1] = Matrix{T}(Z)
     MPO([tensor1, fill(tensor2, n-2)..., tensor3])
+end
+
+function transverse_ising_mpo(::Type{T}, n::Int, h::Real) where T
+    @assert n > 1
+    tensor1 = zeros(T, 1, 2, 2, 3)
+    tensor2 = zeros(T, 3, 2, 2, 3)
+    tensor3 = zeros(T, 3, 2, 2, 1)
+    tensor1[1, :, :, 1] = tensor2[1, :, :, 1] = tensor2[3, :, :, 3] = tensor3[3, :, :, 1] = Matrix{T}(I2)
+    tensor1[1, :, :, 2] = tensor2[2, :, :, 3] = tensor2[1, :, :, 2] = tensor3[2, :, :, 1] = Matrix{T}(Z)
+    tensor1[1, :, :, 3] = tensor2[1, :, :, 3] = tensor3[1, :, :, 1] = Matrix{T}(X) .* h
+    MPO([tensor1, fill(tensor2, n-2)..., tensor3])
 end

test/mpo.jl

@@ -43,4 +43,20 @@ end
     @test nsite(mpo) == n
     h = EasyBuild.heisenberg(n; periodic=false)
     @test mat(mpo) ≈ mat(h)
+end
+
+@testset "transverse ising" begin
+    n = 7
+    h = 0.0
+    mpo = transverse_ising_mpo(ComplexF64, n, h)
+    @test nsite(mpo) == n
+    h = EasyBuild.transverse_ising(n, h; periodic=false)
+    @test mat(mpo) ≈ mat(h)
+
+    n = 7
+    h = 0.2
+    mpo = transverse_ising_mpo(ComplexF64, n, h)
+    @test nsite(mpo) == n
+    h = EasyBuild.transverse_ising(n, h; periodic=false)
+    @test mat(mpo) ≈ mat(h)
 end