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alessandro-santini · Jun 15, 2022 · 27ace1f · 27ace1f
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commit 27ace1f
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Showing 4 changed files with 24 additions and 7 deletions.
diff --git a/algorithms/__pycache__/iTimeEvolvingBlockDecimation.cpython-38.pyc b/algorithms/__pycache__/iTimeEvolvingBlockDecimation.cpython-38.pyc
diff --git a/algorithms/iTimeEvolvingBlockDecimation.py b/algorithms/iTimeEvolvingBlockDecimation.py
@@ -42,15 +42,23 @@ def set_U(self,dt,order=1):
         if order == 1:
             self.U.append(expm(-1j*H*dt).reshape(d,d,d,d).transpose(2,3,0,1))
             self.U.append(expm(-1j*H*dt).reshape(d,d,d,d).transpose(2,3,0,1))
-        if order == 2:
+        elif order == 2:
             self.U.append(expm(-1j*H*dt/2).reshape(d,d,d,d).transpose(2,3,0,1))
             self.U.append(expm(-1j*H*dt).reshape(d,d,d,d).transpose(2,3,0,1))
             self.U.append(expm(-1j*H*dt/2).reshape(d,d,d,d).transpose(2,3,0,1))
-        if order == 4:
+        elif order == 3:
+            c_trot = np.zeros(3)
+            d_trot = np.zeros(3)
+            c_trot[0] = 1; c_trot[1] = -2/3; c_trot[2] = 2/3
+            d_trot[0] = -1/24; d_trot[1] = 3/4; d_trot[2] = 7/24
+            for i in range(3):
+                self.U.append(expm(-1j*H*c_trot[i]*dt).reshape(d,d,d,d).transpose(2,3,0,1))
+                self.U.append(expm(-1j*H*d_trot[i]*dt).reshape(d,d,d,d).transpose(2,3,0,1))
+        elif order == 4:
             tau1 = 1./(4.-4.**(1./3.))*dt; tau2=tau1;
             tau3 = dt-2*tau1-2*tau2
-            for tau in [tau1/2,tau1,(tau1+tau2)/2,tau2,(tau2+tau3)/2,tau3,tau3/2 ]:
-                self.U.append(expm(-1j*H*tau/2).reshape(d,d,d,d).transpose(2,3,0,1))
+            for tau in [tau1/2,tau1,(tau1+tau2)/2,tau2,(tau2+tau3)/2,tau3,(tau2+tau3)/2,tau2,(tau1+tau2)/2,tau1,tau1/2]:
+                self.U.append(expm(-1j*H*tau).reshape(d,d,d,d).transpose(2,3,0,1))
 
     def time_step(self):
         for K in self.U:
@@ -63,7 +71,7 @@ def time_step(self):
             self.psi.B2 = V
             self.psi.B1 = oe.contract('i,ijk,k->ijk',1./self.psi.Sv,U,S)
             self.psi.Sv, self.psi.B1, self.psi.B2 = S, self.psi.B2, self.psi.B1
-            
+
     def err_normalization(self):
         return np.abs(self.psi.compute_norm()-1)
 

diff --git a/spin_systems/__pycache__/iHamiltonians.cpython-38.pyc b/spin_systems/__pycache__/iHamiltonians.cpython-38.pyc
diff --git a/spin_systems/iHamiltonians.py b/spin_systems/iHamiltonians.py
@@ -12,7 +12,16 @@ def IsingChainWithAncilla(J=1., h_z=0.25, h_x=0.):
     sz_anc = np.kron(Id2,sz)
     sx_anc = np.kron(Id2,sx)
 
-    H  = -J*(np.kron(sx_sys,sx_sys))-h_z*(np.kron(sz_sys,Id4)+np.kron(Id4,sz_sys))-h_x*(np.kron(sx_sys,Id4)+np.kron(Id4,sx_sys))
-    H  += -J*(np.kron(sx_anc,sx_anc))-h_z*(np.kron(sz_anc,Id4)+np.kron(Id4,sz_anc))-h_x*(np.kron(sx_anc,Id4)+np.kron(Id4,sx_anc))
+    H  = -J*(np.kron(sx_sys,sx_sys))-h_z/2*(np.kron(sz_sys,Id4)+np.kron(Id4,sz_sys))-h_x/2*(np.kron(sx_sys,Id4)+np.kron(Id4,sx_sys))
+    H  += -J*(np.kron(sx_anc,sx_anc))-h_z/2*(np.kron(sz_anc,Id4)+np.kron(Id4,sz_anc))-h_x/2*(np.kron(sx_anc,Id4)+np.kron(Id4,sx_anc))
+
+    return H
+
+def IsingChain(J=1., h_z=0.25, h_x=0.):
+    sz = np.array([[1,0],[0,-1]])
+    sx = np.array([[0,1],[1,0]])
+    Id2 = np.eye(2)
+
+    H  = -J*(np.kron(sx,sx))-h_z/2*(np.kron(sz,Id2)+np.kron(Id2,sz))-h_x/2*(np.kron(sx,Id2)+np.kron(Id2,sx))
 
     return H